Commit b8399819 authored by Arvind Sankar's avatar Arvind Sankar Committed by Herbert Xu
Browse files

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



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: default avatarArvind Sankar <nivedita@alum.mit.edu>
Reviewed-by: default avatarEric Biggers <ebiggers@google.com>
Acked-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 7a4295f6

lib/crypto/sha256.c

+5 −6
Original line number Diff line number Diff line
@@ -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];

}



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 W[64];

	int i;



	/* 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[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)

{

	unsigned int partial, done;

	const u8 *src;

	u32 W[64];



	partial = sctx->count & 0x3f;

	sctx->count += len;
@@ -223,11 +220,13 @@ void sha256_update(struct sha256_state *sctx, const u8 *data, unsigned int len) 
		}



		do {

			sha256_transform(sctx->state, src);

			sha256_transform(sctx->state, src, W);

			done += 64;

			src = data + done;

		} while (done + 63 < len);



		memzero_explicit(W, sizeof(W));



		partial = 0;

	}

	memcpy(sctx->buf + partial, src, len - done);