Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
crypto: x86/ghash - add comment and fix broken link
Add a comment that explains what ghash_setkey() is doing, as it's hard
to understand otherwise. Also fix a broken hyperlink.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
authored by
Eric Biggers
and committed by
Herbert Xu
750426d6
f1740751
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arch/x86/crypto/ghash-clmulni-intel_asm.S
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arch/x86/crypto/ghash-clmulni-intel_asm.S
···
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* instructions. This file contains accelerated part of ghash
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* implementation. More information about PCLMULQDQ can be found at:
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*
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* http://software.intel.com/en-us/articles/carry-less-multiplication-and-its-usage-for-computing-the-gcm-mode/
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* https://www.intel.com/content/dam/develop/external/us/en/documents/clmul-wp-rev-2-02-2014-04-20.pdf
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*
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* Copyright (c) 2009 Intel Corp.
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* Author: Huang Ying <ying.huang@intel.com>
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arch/x86/crypto/ghash-clmulni-intel_glue.c
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arch/x86/crypto/ghash-clmulni-intel_glue.c
···
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if (keylen != GHASH_BLOCK_SIZE)
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return -EINVAL;
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/* perform multiplication by 'x' in GF(2^128) */
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/*
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* GHASH maps bits to polynomial coefficients backwards, which makes it
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* hard to implement. But it can be shown that the GHASH multiplication
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*
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* D * K (mod x^128 + x^7 + x^2 + x + 1)
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*
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* (where D is a data block and K is the key) is equivalent to:
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*
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* bitreflect(D) * bitreflect(K) * x^(-127)
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* (mod x^128 + x^127 + x^126 + x^121 + 1)
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*
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* So, the code below precomputes:
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*
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* bitreflect(K) * x^(-127) (mod x^128 + x^127 + x^126 + x^121 + 1)
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*
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* ... but in Montgomery form (so that Montgomery multiplication can be
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* used), i.e. with an extra x^128 factor, which means actually:
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*
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* bitreflect(K) * x (mod x^128 + x^127 + x^126 + x^121 + 1)
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*
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* The within-a-byte part of bitreflect() cancels out GHASH's built-in
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* reflection, and thus bitreflect() is actually a byteswap.
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*/
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a = get_unaligned_be64(key);
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b = get_unaligned_be64(key + 8);
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ctx->shash.a = cpu_to_le64((a << 1) | (b >> 63));
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ctx->shash.b = cpu_to_le64((b << 1) | (a >> 63));
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if (a >> 63)
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ctx->shash.a ^= cpu_to_le64((u64)0xc2 << 56);
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return 0;
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}
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