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2019-01-10crypto: adiantum - initialize crypto_spawn::instEric Biggers1-0/+4
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>
2018-12-13crypto: adiantum - fix leaking reference to hash algorithmEric Biggers1-4/+5
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>
2018-12-13crypto: adiantum - adjust some comments to match latest paperEric Biggers1-16/+19
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>
2018-12-13crypto: adiantum - propagate CRYPTO_ALG_ASYNC flag to instanceEric Biggers1-0/+2
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>
2018-11-20crypto: adiantum - add Adiantum supportEric Biggers1-0/+658
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>