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2019-07-26crypto: aes - create AES library based on the fixed time AES codeArd Biesheuvel1-300/+3
Take the existing small footprint and mostly time invariant C code and turn it into a AES library that can be used for non-performance critical, casual use of AES, and as a fallback for, e.g., SIMD code that needs a secondary path that can be taken in contexts where the SIMD unit is off limits (e.g., in hard interrupts taken from kernel context) Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2019-07-26crypto: aes/fixed-time - align key schedule with other implementationsArd Biesheuvel1-31/+21
The fixed time AES code mangles the key schedule so that xoring the first round key with values at fixed offsets across the Sbox produces the correct value. This primes the D-cache with the entire Sbox before any data dependent lookups are done, making it more difficult to infer key bits from timing variances when the plaintext is known. The downside of this approach is that it renders the key schedule incompatible with other implementations of AES in the kernel, which makes it cumbersome to use this implementation as a fallback for SIMD based AES in contexts where this is not allowed. So let's tweak the fixed Sbox indexes so that they add up to zero under the xor operation. While at it, increase the granularity to 16 bytes so we cover the entire Sbox even on systems with 16 byte cachelines. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2019-06-19treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500Thomas Gleixner1-4/+1
Based on 2 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation # extracted by the scancode license scanner the SPDX license identifier GPL-2.0-only has been chosen to replace the boilerplate/reference in 4122 file(s). Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Enrico Weigelt <info@metux.net> Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Reviewed-by: Allison Randal <allison@lohutok.net> Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-11-09crypto: aes_ti - disable interrupts while accessing S-boxEric Biggers1-0/+18
In the "aes-fixed-time" AES implementation, disable interrupts while accessing the S-box, in order to make cache-timing attacks more difficult. Previously it was possible for the CPU to be interrupted while the S-box was loaded into L1 cache, potentially evicting the cachelines and causing later table lookups to be time-variant. In tests I did on x86 and ARM, this doesn't affect performance significantly. Responsiveness is potentially a concern, but interrupts are only disabled for a single AES block. Note that even after this change, the implementation still isn't necessarily guaranteed to be constant-time; see https://cr.yp.to/antiforgery/cachetiming-20050414.pdf for a discussion of the many difficulties involved in writing truly constant-time AES software. But it's valuable to make such attacks more difficult. Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2017-06-19crypto: aes_ti - fix comment for MixColumns stepEric Biggers1-1/+1
mix_columns() contains a comment which shows the matrix used by the MixColumns step of AES, but the last entry in this matrix was incorrect Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2017-02-11crypto: aes - add generic time invariant AES cipherArd Biesheuvel1-0/+375
Lookup table based AES is sensitive to timing attacks, which is due to the fact that such table lookups are data dependent, and the fact that 8 KB worth of tables covers a significant number of cachelines on any architecture, resulting in an exploitable correlation between the key and the processing time for known plaintexts. For network facing algorithms such as CTR, CCM or GCM, this presents a security risk, which is why arch specific AES ports are typically time invariant, either through the use of special instructions, or by using SIMD algorithms that don't rely on table lookups. For generic code, this is difficult to achieve without losing too much performance, but we can improve the situation significantly by switching to an implementation that only needs 256 bytes of table data (the actual S-box itself), which can be prefetched at the start of each block to eliminate data dependent latencies. This code encrypts at ~25 cycles per byte on ARM Cortex-A57 (while the ordinary generic AES driver manages 18 cycles per byte on this hardware). Decryption is substantially slower. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>