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crypto: lib/sha256 - Clear W[] in sha256_update() instead of sha256_transform()

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The temporary W[] array is currently zeroed out once every call to
sha256_transform(), i.e. once every 64 bytes of input data. Moving it to
sha256_update() instead so that it is cleared only once per update can
save about 2-3% of the total time taken to compute the digest, with a
reasonable memset() implementation, and considerably more (~20%) with a
bad one (eg the x86 purgatory currently uses a memset() coded in C).

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Arvind Sankar 2020-10-25 10:31:17 -04:00 committed by Herbert Xu
parent 7a4295f6c9
commit b8399819b2
1 changed files with 5 additions and 6 deletions
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11
lib/crypto/sha256.c
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@ -43,10 +43,9 @@ static inline void BLEND_OP(int I, u32 *W)
W[I] = s1(W[I-2]) + W[I-7] + s0(W[I-15]) + W[I-16]; W[I] = s1(W[I-2]) + W[I-7] + s0(W[I-15]) + W[I-16];
} }
static void sha256_transform(u32 *state, const u8 *input) static void sha256_transform(u32 *state, const u8 *input, u32 *W)
{ {
u32 a, b, c, d, e, f, g, h, t1, t2; u32 a, b, c, d, e, f, g, h, t1, t2;
u32 W[64];
int i; int i;
/* load the input */ /* load the input */
@ -200,15 +199,13 @@ static void sha256_transform(u32 *state, const u8 *input)
state[0] += a; state[1] += b; state[2] += c; state[3] += d; state[0] += a; state[1] += b; state[2] += c; state[3] += d;
state[4] += e; state[5] += f; state[6] += g; state[7] += h; state[4] += e; state[5] += f; state[6] += g; state[7] += h;
/* clear any sensitive info... */
memzero_explicit(W, 64 * sizeof(u32));
} }
void sha256_update(struct sha256_state *sctx, const u8 *data, unsigned int len) void sha256_update(struct sha256_state *sctx, const u8 *data, unsigned int len)
{ {
unsigned int partial, done; unsigned int partial, done;
const u8 *src; const u8 *src;
u32 W[64];
partial = sctx->count & 0x3f; partial = sctx->count & 0x3f;
sctx->count += len; sctx->count += len;
@ -223,11 +220,13 @@ void sha256_update(struct sha256_state *sctx, const u8 *data, unsigned int len)
} }
do { do {
sha256_transform(sctx->state, src); sha256_transform(sctx->state, src, W);
done += 64; done += 64;
src = data + done; src = data + done;
} while (done + 63 < len); } while (done + 63 < len);
memzero_explicit(W, sizeof(W));
partial = 0; partial = 0;
} }
memcpy(sctx->buf + partial, src, len - done); memcpy(sctx->buf + partial, src, len - done);