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crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
// SPDX-License-Identifier: GPL-2.0
/*
* Adiantum length-preserving encryption mode
*
* Copyright 2018 Google LLC
*/
/*
* Adiantum is a tweakable, length-preserving encryption mode designed for fast
* and secure disk encryption, especially on CPUs without dedicated crypto
* instructions. Adiantum encrypts each sector using the XChaCha12 stream
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* cipher, two passes of an ε-almost-∆-universal (ε-∆U) hash function based on
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
* NH and Poly1305, and an invocation of the AES-256 block cipher on a single
* 16-byte block. See the paper for details:
*
* Adiantum: length-preserving encryption for entry-level processors
* (https://eprint.iacr.org/2018/720.pdf)
*
* For flexibility, this implementation also allows other ciphers:
*
* - Stream cipher: XChaCha12 or XChaCha20
* - Block cipher: any with a 128-bit block size and 256-bit key
*
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* This implementation doesn't currently allow other ε-∆U hash functions, i.e.
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
* HPolyC is not supported. This is because Adiantum is ~20% faster than HPolyC
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* but still provably as secure, and also the ε-∆U hash function of HBSH is
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
* formally defined to take two inputs (tweak, message) which makes it difficult
* to wrap with the crypto_shash API. Rather, some details need to be handled
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* here. Nevertheless, if needed in the future, support for other ε-∆U hash
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
* functions could be added here.
*/
#include <crypto/b128ops.h>
#include <crypto/chacha.h>
#include <crypto/internal/hash.h>
#include <crypto/internal/skcipher.h>
#include <crypto/nhpoly1305.h>
#include <crypto/scatterwalk.h>
#include <linux/module.h>
#include "internal.h"
/*
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* Size of right-hand part of input data, in bytes; also the size of the block
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
* cipher's block size and the hash function's output.
*/
#define BLOCKCIPHER_BLOCK_SIZE 16
/* Size of the block cipher key (K_E) in bytes */
#define BLOCKCIPHER_KEY_SIZE 32
/* Size of the hash key (K_H) in bytes */
#define HASH_KEY_SIZE (POLY1305_BLOCK_SIZE + NHPOLY1305_KEY_SIZE)
/*
* The specification allows variable-length tweaks, but Linux's crypto API
* currently only allows algorithms to support a single length. The "natural"
* tweak length for Adiantum is 16, since that fits into one Poly1305 block for
* the best performance. But longer tweaks are useful for fscrypt, to avoid
* needing to derive per-file keys. So instead we use two blocks, or 32 bytes.
*/
#define TWEAK_SIZE 32
struct adiantum_instance_ctx {
struct crypto_skcipher_spawn streamcipher_spawn;
struct crypto_spawn blockcipher_spawn;
struct crypto_shash_spawn hash_spawn;
};
struct adiantum_tfm_ctx {
struct crypto_skcipher *streamcipher;
struct crypto_cipher *blockcipher;
struct crypto_shash *hash;
struct poly1305_key header_hash_key;
};
struct adiantum_request_ctx {
/*
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* Buffer for right-hand part of data, i.e.
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
*
* P_L => P_M => C_M => C_R when encrypting, or
* C_R => C_M => P_M => P_L when decrypting.
*
* Also used to build the IV for the stream cipher.
*/
union {
u8 bytes[XCHACHA_IV_SIZE];
__le32 words[XCHACHA_IV_SIZE / sizeof(__le32)];
le128 bignum; /* interpret as element of Z/(2^{128}Z) */
} rbuf;
bool enc; /* true if encrypting, false if decrypting */
/*
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* The result of the Poly1305 ε-∆U hash function applied to
* (bulk length, tweak)
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
*/
le128 header_hash;
/* Sub-requests, must be last */
union {
struct shash_desc hash_desc;
struct skcipher_request streamcipher_req;
} u;
};
/*
* Given the XChaCha stream key K_S, derive the block cipher key K_E and the
* hash key K_H as follows:
*
* K_E || K_H || ... = XChaCha(key=K_S, nonce=1||0^191)
*
* Note that this denotes using bits from the XChaCha keystream, which here we
* get indirectly by encrypting a buffer containing all 0's.
*/
static int adiantum_setkey(struct crypto_skcipher *tfm, const u8 *key,
unsigned int keylen)
{
struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
struct {
u8 iv[XCHACHA_IV_SIZE];
u8 derived_keys[BLOCKCIPHER_KEY_SIZE + HASH_KEY_SIZE];
struct scatterlist sg;
struct crypto_wait wait;
struct skcipher_request req; /* must be last */
} *data;
u8 *keyp;
int err;
/* Set the stream cipher key (K_S) */
crypto_skcipher_clear_flags(tctx->streamcipher, CRYPTO_TFM_REQ_MASK);
crypto_skcipher_set_flags(tctx->streamcipher,
crypto_skcipher_get_flags(tfm) &
CRYPTO_TFM_REQ_MASK);
err = crypto_skcipher_setkey(tctx->streamcipher, key, keylen);
crypto_skcipher_set_flags(tfm,
crypto_skcipher_get_flags(tctx->streamcipher) &
CRYPTO_TFM_RES_MASK);
if (err)
return err;
/* Derive the subkeys */
data = kzalloc(sizeof(*data) +
crypto_skcipher_reqsize(tctx->streamcipher), GFP_KERNEL);
if (!data)
return -ENOMEM;
data->iv[0] = 1;
sg_init_one(&data->sg, data->derived_keys, sizeof(data->derived_keys));
crypto_init_wait(&data->wait);
skcipher_request_set_tfm(&data->req, tctx->streamcipher);
skcipher_request_set_callback(&data->req, CRYPTO_TFM_REQ_MAY_SLEEP |
CRYPTO_TFM_REQ_MAY_BACKLOG,
crypto_req_done, &data->wait);
skcipher_request_set_crypt(&data->req, &data->sg, &data->sg,
sizeof(data->derived_keys), data->iv);
err = crypto_wait_req(crypto_skcipher_encrypt(&data->req), &data->wait);
if (err)
goto out;
keyp = data->derived_keys;
/* Set the block cipher key (K_E) */
crypto_cipher_clear_flags(tctx->blockcipher, CRYPTO_TFM_REQ_MASK);
crypto_cipher_set_flags(tctx->blockcipher,
crypto_skcipher_get_flags(tfm) &
CRYPTO_TFM_REQ_MASK);
err = crypto_cipher_setkey(tctx->blockcipher, keyp,
BLOCKCIPHER_KEY_SIZE);
crypto_skcipher_set_flags(tfm,
crypto_cipher_get_flags(tctx->blockcipher) &
CRYPTO_TFM_RES_MASK);
if (err)
goto out;
keyp += BLOCKCIPHER_KEY_SIZE;
/* Set the hash key (K_H) */
poly1305_core_setkey(&tctx->header_hash_key, keyp);
keyp += POLY1305_BLOCK_SIZE;
crypto_shash_clear_flags(tctx->hash, CRYPTO_TFM_REQ_MASK);
crypto_shash_set_flags(tctx->hash, crypto_skcipher_get_flags(tfm) &
CRYPTO_TFM_REQ_MASK);
err = crypto_shash_setkey(tctx->hash, keyp, NHPOLY1305_KEY_SIZE);
crypto_skcipher_set_flags(tfm, crypto_shash_get_flags(tctx->hash) &
CRYPTO_TFM_RES_MASK);
keyp += NHPOLY1305_KEY_SIZE;
WARN_ON(keyp != &data->derived_keys[ARRAY_SIZE(data->derived_keys)]);
out:
kzfree(data);
return err;
}
/* Addition in Z/(2^{128}Z) */
static inline void le128_add(le128 *r, const le128 *v1, const le128 *v2)
{
u64 x = le64_to_cpu(v1->b);
u64 y = le64_to_cpu(v2->b);
r->b = cpu_to_le64(x + y);
r->a = cpu_to_le64(le64_to_cpu(v1->a) + le64_to_cpu(v2->a) +
(x + y < x));
}
/* Subtraction in Z/(2^{128}Z) */
static inline void le128_sub(le128 *r, const le128 *v1, const le128 *v2)
{
u64 x = le64_to_cpu(v1->b);
u64 y = le64_to_cpu(v2->b);
r->b = cpu_to_le64(x - y);
r->a = cpu_to_le64(le64_to_cpu(v1->a) - le64_to_cpu(v2->a) -
(x - y > x));
}
/*
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* Apply the Poly1305 ε-∆U hash function to (bulk length, tweak) and save the
* result to rctx->header_hash. This is the calculation
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
*
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
* H_T ← Poly1305_{K_T}(bin_{128}(|L|) || T)
*
* from the procedure in section 6.4 of the Adiantum paper. The resulting value
* is reused in both the first and second hash steps. Specifically, it's added
* to the result of an independently keyed ε-∆U hash function (for equal length
* inputs only) taken over the left-hand part (the "bulk") of the message, to
* give the overall Adiantum hash of the (tweak, left-hand part) pair.
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
*/
static void adiantum_hash_header(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
struct {
__le64 message_bits;
__le64 padding;
} header = {
.message_bits = cpu_to_le64((u64)bulk_len * 8)
};
struct poly1305_state state;
poly1305_core_init(&state);
BUILD_BUG_ON(sizeof(header) % POLY1305_BLOCK_SIZE != 0);
poly1305_core_blocks(&state, &tctx->header_hash_key,
&header, sizeof(header) / POLY1305_BLOCK_SIZE);
BUILD_BUG_ON(TWEAK_SIZE % POLY1305_BLOCK_SIZE != 0);
poly1305_core_blocks(&state, &tctx->header_hash_key, req->iv,
TWEAK_SIZE / POLY1305_BLOCK_SIZE);
poly1305_core_emit(&state, &rctx->header_hash);
}
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
/* Hash the left-hand part (the "bulk") of the message using NHPoly1305 */
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
static int adiantum_hash_message(struct skcipher_request *req,
struct scatterlist *sgl, le128 *digest)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
struct shash_desc *hash_desc = &rctx->u.hash_desc;
struct sg_mapping_iter miter;
unsigned int i, n;
int err;
hash_desc->tfm = tctx->hash;
hash_desc->flags = 0;
err = crypto_shash_init(hash_desc);
if (err)
return err;
sg_miter_start(&miter, sgl, sg_nents(sgl),
SG_MITER_FROM_SG | SG_MITER_ATOMIC);
for (i = 0; i < bulk_len; i += n) {
sg_miter_next(&miter);
n = min_t(unsigned int, miter.length, bulk_len - i);
err = crypto_shash_update(hash_desc, miter.addr, n);
if (err)
break;
}
sg_miter_stop(&miter);
if (err)
return err;
return crypto_shash_final(hash_desc, (u8 *)digest);
}
/* Continue Adiantum encryption/decryption after the stream cipher step */
static int adiantum_finish(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
le128 digest;
int err;
/* If decrypting, decrypt C_M with the block cipher to get P_M */
if (!rctx->enc)
crypto_cipher_decrypt_one(tctx->blockcipher, rctx->rbuf.bytes,
rctx->rbuf.bytes);
/*
* Second hash step
* enc: C_R = C_M - H_{K_H}(T, C_L)
* dec: P_R = P_M - H_{K_H}(T, P_L)
*/
err = adiantum_hash_message(req, req->dst, &digest);
if (err)
return err;
le128_add(&digest, &digest, &rctx->header_hash);
le128_sub(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &digest);
scatterwalk_map_and_copy(&rctx->rbuf.bignum, req->dst,
bulk_len, BLOCKCIPHER_BLOCK_SIZE, 1);
return 0;
}
static void adiantum_streamcipher_done(struct crypto_async_request *areq,
int err)
{
struct skcipher_request *req = areq->data;
if (!err)
err = adiantum_finish(req);
skcipher_request_complete(req, err);
}
static int adiantum_crypt(struct skcipher_request *req, bool enc)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
unsigned int stream_len;
le128 digest;
int err;
if (req->cryptlen < BLOCKCIPHER_BLOCK_SIZE)
return -EINVAL;
rctx->enc = enc;
/*
* First hash step
* enc: P_M = P_R + H_{K_H}(T, P_L)
* dec: C_M = C_R + H_{K_H}(T, C_L)
*/
adiantum_hash_header(req);
err = adiantum_hash_message(req, req->src, &digest);
if (err)
return err;
le128_add(&digest, &digest, &rctx->header_hash);
scatterwalk_map_and_copy(&rctx->rbuf.bignum, req->src,
bulk_len, BLOCKCIPHER_BLOCK_SIZE, 0);
le128_add(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &digest);
/* If encrypting, encrypt P_M with the block cipher to get C_M */
if (enc)
crypto_cipher_encrypt_one(tctx->blockcipher, rctx->rbuf.bytes,
rctx->rbuf.bytes);
/* Initialize the rest of the XChaCha IV (first part is C_M) */
BUILD_BUG_ON(BLOCKCIPHER_BLOCK_SIZE != 16);
BUILD_BUG_ON(XCHACHA_IV_SIZE != 32); /* nonce || stream position */
rctx->rbuf.words[4] = cpu_to_le32(1);
rctx->rbuf.words[5] = 0;
rctx->rbuf.words[6] = 0;
rctx->rbuf.words[7] = 0;
/*
* XChaCha needs to be done on all the data except the last 16 bytes;
* for disk encryption that usually means 4080 or 496 bytes. But ChaCha
* implementations tend to be most efficient when passed a whole number
* of 64-byte ChaCha blocks, or sometimes even a multiple of 256 bytes.
* And here it doesn't matter whether the last 16 bytes are written to,
* as the second hash step will overwrite them. Thus, round the XChaCha
* length up to the next 64-byte boundary if possible.
*/
stream_len = bulk_len;
if (round_up(stream_len, CHACHA_BLOCK_SIZE) <= req->cryptlen)
stream_len = round_up(stream_len, CHACHA_BLOCK_SIZE);
skcipher_request_set_tfm(&rctx->u.streamcipher_req, tctx->streamcipher);
skcipher_request_set_crypt(&rctx->u.streamcipher_req, req->src,
req->dst, stream_len, &rctx->rbuf);
skcipher_request_set_callback(&rctx->u.streamcipher_req,
req->base.flags,
adiantum_streamcipher_done, req);
return crypto_skcipher_encrypt(&rctx->u.streamcipher_req) ?:
adiantum_finish(req);
}
static int adiantum_encrypt(struct skcipher_request *req)
{
return adiantum_crypt(req, true);
}
static int adiantum_decrypt(struct skcipher_request *req)
{
return adiantum_crypt(req, false);
}
static int adiantum_init_tfm(struct crypto_skcipher *tfm)
{
struct skcipher_instance *inst = skcipher_alg_instance(tfm);
struct adiantum_instance_ctx *ictx = skcipher_instance_ctx(inst);
struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
struct crypto_skcipher *streamcipher;
struct crypto_cipher *blockcipher;
struct crypto_shash *hash;
unsigned int subreq_size;
int err;
streamcipher = crypto_spawn_skcipher(&ictx->streamcipher_spawn);
if (IS_ERR(streamcipher))
return PTR_ERR(streamcipher);
blockcipher = crypto_spawn_cipher(&ictx->blockcipher_spawn);
if (IS_ERR(blockcipher)) {
err = PTR_ERR(blockcipher);
goto err_free_streamcipher;
}
hash = crypto_spawn_shash(&ictx->hash_spawn);
if (IS_ERR(hash)) {
err = PTR_ERR(hash);
goto err_free_blockcipher;
}
tctx->streamcipher = streamcipher;
tctx->blockcipher = blockcipher;
tctx->hash = hash;
BUILD_BUG_ON(offsetofend(struct adiantum_request_ctx, u) !=
sizeof(struct adiantum_request_ctx));
subreq_size = max(FIELD_SIZEOF(struct adiantum_request_ctx,
u.hash_desc) +
crypto_shash_descsize(hash),
FIELD_SIZEOF(struct adiantum_request_ctx,
u.streamcipher_req) +
crypto_skcipher_reqsize(streamcipher));
crypto_skcipher_set_reqsize(tfm,
offsetof(struct adiantum_request_ctx, u) +
subreq_size);
return 0;
err_free_blockcipher:
crypto_free_cipher(blockcipher);
err_free_streamcipher:
crypto_free_skcipher(streamcipher);
return err;
}
static void adiantum_exit_tfm(struct crypto_skcipher *tfm)
{
struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
crypto_free_skcipher(tctx->streamcipher);
crypto_free_cipher(tctx->blockcipher);
crypto_free_shash(tctx->hash);
}
static void adiantum_free_instance(struct skcipher_instance *inst)
{
struct adiantum_instance_ctx *ictx = skcipher_instance_ctx(inst);
crypto_drop_skcipher(&ictx->streamcipher_spawn);
crypto_drop_spawn(&ictx->blockcipher_spawn);
crypto_drop_shash(&ictx->hash_spawn);
kfree(inst);
}
/*
* Check for a supported set of inner algorithms.
* See the comment at the beginning of this file.
*/
static bool adiantum_supported_algorithms(struct skcipher_alg *streamcipher_alg,
struct crypto_alg *blockcipher_alg,
struct shash_alg *hash_alg)
{
if (strcmp(streamcipher_alg->base.cra_name, "xchacha12") != 0 &&
strcmp(streamcipher_alg->base.cra_name, "xchacha20") != 0)
return false;
if (blockcipher_alg->cra_cipher.cia_min_keysize > BLOCKCIPHER_KEY_SIZE ||
blockcipher_alg->cra_cipher.cia_max_keysize < BLOCKCIPHER_KEY_SIZE)
return false;
if (blockcipher_alg->cra_blocksize != BLOCKCIPHER_BLOCK_SIZE)
return false;
if (strcmp(hash_alg->base.cra_name, "nhpoly1305") != 0)
return false;
return true;
}
static int adiantum_create(struct crypto_template *tmpl, struct rtattr **tb)
{
struct crypto_attr_type *algt;
const char *streamcipher_name;
const char *blockcipher_name;
const char *nhpoly1305_name;
struct skcipher_instance *inst;
struct adiantum_instance_ctx *ictx;
struct skcipher_alg *streamcipher_alg;
struct crypto_alg *blockcipher_alg;
struct crypto_alg *_hash_alg;
struct shash_alg *hash_alg;
int err;
algt = crypto_get_attr_type(tb);
if (IS_ERR(algt))
return PTR_ERR(algt);
if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
return -EINVAL;
streamcipher_name = crypto_attr_alg_name(tb[1]);
if (IS_ERR(streamcipher_name))
return PTR_ERR(streamcipher_name);
blockcipher_name = crypto_attr_alg_name(tb[2]);
if (IS_ERR(blockcipher_name))
return PTR_ERR(blockcipher_name);
nhpoly1305_name = crypto_attr_alg_name(tb[3]);
if (nhpoly1305_name == ERR_PTR(-ENOENT))
nhpoly1305_name = "nhpoly1305";
if (IS_ERR(nhpoly1305_name))
return PTR_ERR(nhpoly1305_name);
inst = kzalloc(sizeof(*inst) + sizeof(*ictx), GFP_KERNEL);
if (!inst)
return -ENOMEM;
ictx = skcipher_instance_ctx(inst);
/* Stream cipher, e.g. "xchacha12" */
crypto: adiantum - initialize crypto_spawn::inst crypto_grab_*() doesn't set crypto_spawn::inst, so templates must set it beforehand. Otherwise it will be left NULL, which causes a crash in certain cases where algorithms are dynamically loaded/unloaded. E.g. with CONFIG_CRYPTO_CHACHA20_X86_64=m, the following caused a crash: insmod chacha-x86_64.ko python -c 'import socket; socket.socket(socket.AF_ALG, 5, 0).bind(("skcipher", "adiantum(xchacha12,aes)"))' rmmod chacha-x86_64.ko python -c 'import socket; socket.socket(socket.AF_ALG, 5, 0).bind(("skcipher", "adiantum(xchacha12,aes)"))' Fixes: 059c2a4d8e16 ("crypto: adiantum - add Adiantum support") Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2019-01-06 20:46:05 +00:00
crypto_set_skcipher_spawn(&ictx->streamcipher_spawn,
skcipher_crypto_instance(inst));
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
err = crypto_grab_skcipher(&ictx->streamcipher_spawn, streamcipher_name,
0, crypto_requires_sync(algt->type,
algt->mask));
if (err)
goto out_free_inst;
streamcipher_alg = crypto_spawn_skcipher_alg(&ictx->streamcipher_spawn);
/* Block cipher, e.g. "aes" */
crypto: adiantum - initialize crypto_spawn::inst crypto_grab_*() doesn't set crypto_spawn::inst, so templates must set it beforehand. Otherwise it will be left NULL, which causes a crash in certain cases where algorithms are dynamically loaded/unloaded. E.g. with CONFIG_CRYPTO_CHACHA20_X86_64=m, the following caused a crash: insmod chacha-x86_64.ko python -c 'import socket; socket.socket(socket.AF_ALG, 5, 0).bind(("skcipher", "adiantum(xchacha12,aes)"))' rmmod chacha-x86_64.ko python -c 'import socket; socket.socket(socket.AF_ALG, 5, 0).bind(("skcipher", "adiantum(xchacha12,aes)"))' Fixes: 059c2a4d8e16 ("crypto: adiantum - add Adiantum support") Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2019-01-06 20:46:05 +00:00
crypto_set_spawn(&ictx->blockcipher_spawn,
skcipher_crypto_instance(inst));
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
err = crypto_grab_spawn(&ictx->blockcipher_spawn, blockcipher_name,
CRYPTO_ALG_TYPE_CIPHER, CRYPTO_ALG_TYPE_MASK);
if (err)
goto out_drop_streamcipher;
blockcipher_alg = ictx->blockcipher_spawn.alg;
crypto: adiantum - adjust some comments to match latest paper The 2018-11-28 revision of the Adiantum paper has revised some notation: - 'M' was replaced with 'L' (meaning "Left", for the left-hand part of the message) in the definition of Adiantum hashing, to avoid confusion with the full message - ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U - "block" is now used only to mean block cipher and Poly1305 blocks Also, Adiantum hashing was moved from the appendix to the main paper. To avoid confusion, update relevant comments in the code to match. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-06 22:21:59 +00:00
/* NHPoly1305 ε-∆U hash function */
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
_hash_alg = crypto_alg_mod_lookup(nhpoly1305_name,
CRYPTO_ALG_TYPE_SHASH,
CRYPTO_ALG_TYPE_MASK);
if (IS_ERR(_hash_alg)) {
err = PTR_ERR(_hash_alg);
goto out_drop_blockcipher;
}
hash_alg = __crypto_shash_alg(_hash_alg);
err = crypto_init_shash_spawn(&ictx->hash_spawn, hash_alg,
skcipher_crypto_instance(inst));
crypto: adiantum - fix leaking reference to hash algorithm crypto_alg_mod_lookup() takes a reference to the hash algorithm but crypto_init_shash_spawn() doesn't take ownership of it, hence the reference needs to be dropped in adiantum_create(). Fixes: 059c2a4d8e16 ("crypto: adiantum - add Adiantum support") Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-10 19:45:58 +00:00
if (err)
goto out_put_hash;
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
/* Check the set of algorithms */
if (!adiantum_supported_algorithms(streamcipher_alg, blockcipher_alg,
hash_alg)) {
pr_warn("Unsupported Adiantum instantiation: (%s,%s,%s)\n",
streamcipher_alg->base.cra_name,
blockcipher_alg->cra_name, hash_alg->base.cra_name);
err = -EINVAL;
goto out_drop_hash;
}
/* Instance fields */
err = -ENAMETOOLONG;
if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
"adiantum(%s,%s)", streamcipher_alg->base.cra_name,
blockcipher_alg->cra_name) >= CRYPTO_MAX_ALG_NAME)
goto out_drop_hash;
if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
"adiantum(%s,%s,%s)",
streamcipher_alg->base.cra_driver_name,
blockcipher_alg->cra_driver_name,
hash_alg->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
goto out_drop_hash;
crypto: adiantum - propagate CRYPTO_ALG_ASYNC flag to instance If the stream cipher implementation is asynchronous, then the Adiantum instance must be flagged as asynchronous as well. Otherwise someone asking for a synchronous algorithm can get an asynchronous algorithm. There are no asynchronous xchacha12 or xchacha20 implementations yet which makes this largely a theoretical issue, but it should be fixed. Fixes: 059c2a4d8e16 ("crypto: adiantum - add Adiantum support") Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-05 00:46:54 +00:00
inst->alg.base.cra_flags = streamcipher_alg->base.cra_flags &
CRYPTO_ALG_ASYNC;
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
inst->alg.base.cra_blocksize = BLOCKCIPHER_BLOCK_SIZE;
inst->alg.base.cra_ctxsize = sizeof(struct adiantum_tfm_ctx);
inst->alg.base.cra_alignmask = streamcipher_alg->base.cra_alignmask |
hash_alg->base.cra_alignmask;
/*
* The block cipher is only invoked once per message, so for long
* messages (e.g. sectors for disk encryption) its performance doesn't
* matter as much as that of the stream cipher and hash function. Thus,
* weigh the block cipher's ->cra_priority less.
*/
inst->alg.base.cra_priority = (4 * streamcipher_alg->base.cra_priority +
2 * hash_alg->base.cra_priority +
blockcipher_alg->cra_priority) / 7;
inst->alg.setkey = adiantum_setkey;
inst->alg.encrypt = adiantum_encrypt;
inst->alg.decrypt = adiantum_decrypt;
inst->alg.init = adiantum_init_tfm;
inst->alg.exit = adiantum_exit_tfm;
inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(streamcipher_alg);
inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(streamcipher_alg);
inst->alg.ivsize = TWEAK_SIZE;
inst->free = adiantum_free_instance;
err = skcipher_register_instance(tmpl, inst);
if (err)
goto out_drop_hash;
crypto: adiantum - fix leaking reference to hash algorithm crypto_alg_mod_lookup() takes a reference to the hash algorithm but crypto_init_shash_spawn() doesn't take ownership of it, hence the reference needs to be dropped in adiantum_create(). Fixes: 059c2a4d8e16 ("crypto: adiantum - add Adiantum support") Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-10 19:45:58 +00:00
crypto_mod_put(_hash_alg);
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
return 0;
out_drop_hash:
crypto_drop_shash(&ictx->hash_spawn);
crypto: adiantum - fix leaking reference to hash algorithm crypto_alg_mod_lookup() takes a reference to the hash algorithm but crypto_init_shash_spawn() doesn't take ownership of it, hence the reference needs to be dropped in adiantum_create(). Fixes: 059c2a4d8e16 ("crypto: adiantum - add Adiantum support") Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-12-10 19:45:58 +00:00
out_put_hash:
crypto_mod_put(_hash_alg);
crypto: adiantum - add Adiantum support Add support for the Adiantum encryption mode. Adiantum was designed by Paul Crowley and is specified by our paper: Adiantum: length-preserving encryption for entry-level processors (https://eprint.iacr.org/2018/720.pdf) See our paper for full details; this patch only provides an overview. Adiantum is a tweakable, length-preserving encryption mode designed for fast and secure disk encryption, especially on CPUs without dedicated crypto instructions. Adiantum encrypts each sector using the XChaCha12 stream cipher, two passes of an ε-almost-∆-universal (εA∆U) hash function, and an invocation of the AES-256 block cipher on a single 16-byte block. On CPUs without AES instructions, Adiantum is much faster than AES-XTS; for example, on ARM Cortex-A7, on 4096-byte sectors Adiantum encryption is about 4 times faster than AES-256-XTS encryption, and decryption about 5 times faster. Adiantum is a specialization of the more general HBSH construction. Our earlier proposal, HPolyC, was also a HBSH specialization, but it used a different εA∆U hash function, one based on Poly1305 only. Adiantum's εA∆U hash function, which is based primarily on the "NH" hash function like that used in UMAC (RFC4418), is about twice as fast as HPolyC's; consequently, Adiantum is about 20% faster than HPolyC. This speed comes with no loss of security: Adiantum is provably just as secure as HPolyC, in fact slightly *more* secure. Like HPolyC, Adiantum's security is reducible to that of XChaCha12 and AES-256, subject to a security bound. XChaCha12 itself has a security reduction to ChaCha12. Therefore, one need not "trust" Adiantum; one need only trust ChaCha12 and AES-256. Note that the εA∆U hash function is only used for its proven combinatorical properties so cannot be "broken". Adiantum is also a true wide-block encryption mode, so flipping any plaintext bit in the sector scrambles the entire ciphertext, and vice versa. No other such mode is available in the kernel currently; doing the same with XTS scrambles only 16 bytes. Adiantum also supports arbitrary-length tweaks and naturally supports any length input >= 16 bytes without needing "ciphertext stealing". For the stream cipher, Adiantum uses XChaCha12 rather than XChaCha20 in order to make encryption feasible on the widest range of devices. Although the 20-round variant is quite popular, the best known attacks on ChaCha are on only 7 rounds, so ChaCha12 still has a substantial security margin; in fact, larger than AES-256's. 12-round Salsa20 is also the eSTREAM recommendation. For the block cipher, Adiantum uses AES-256, despite it having a lower security margin than XChaCha12 and needing table lookups, due to AES's extensive adoption and analysis making it the obvious first choice. Nevertheless, for flexibility this patch also permits the "adiantum" template to be instantiated with XChaCha20 and/or with an alternate block cipher. We need Adiantum support in the kernel for use in dm-crypt and fscrypt, where currently the only other suitable options are block cipher modes such as AES-XTS. A big problem with this is that many low-end mobile devices (e.g. Android Go phones sold primarily in developing countries, as well as some smartwatches) still have CPUs that lack AES instructions, e.g. ARM Cortex-A7. Sadly, AES-XTS encryption is much too slow to be viable on these devices. We did find that some "lightweight" block ciphers are fast enough, but these suffer from problems such as not having much cryptanalysis or being too controversial. The ChaCha stream cipher has excellent performance but is insecure to use directly for disk encryption, since each sector's IV is reused each time it is overwritten. Even restricting the threat model to offline attacks only isn't enough, since modern flash storage devices don't guarantee that "overwrites" are really overwrites, due to wear-leveling. Adiantum avoids this problem by constructing a "tweakable super-pseudorandom permutation"; this is the strongest possible security model for length-preserving encryption. Of course, storing random nonces along with the ciphertext would be the ideal solution. But doing that with existing hardware and filesystems runs into major practical problems; in most cases it would require data journaling (like dm-integrity) which severely degrades performance. Thus, for now length-preserving encryption is still needed. Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 01:26:31 +00:00
out_drop_blockcipher:
crypto_drop_spawn(&ictx->blockcipher_spawn);
out_drop_streamcipher:
crypto_drop_skcipher(&ictx->streamcipher_spawn);
out_free_inst:
kfree(inst);
return err;
}
/* adiantum(streamcipher_name, blockcipher_name [, nhpoly1305_name]) */
static struct crypto_template adiantum_tmpl = {
.name = "adiantum",
.create = adiantum_create,
.module = THIS_MODULE,
};
static int __init adiantum_module_init(void)
{
return crypto_register_template(&adiantum_tmpl);
}
static void __exit adiantum_module_exit(void)
{
crypto_unregister_template(&adiantum_tmpl);
}
module_init(adiantum_module_init);
module_exit(adiantum_module_exit);
MODULE_DESCRIPTION("Adiantum length-preserving encryption mode");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Eric Biggers <ebiggers@google.com>");
MODULE_ALIAS_CRYPTO("adiantum");
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