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crypto: drbg - Clean up loop in drbg_hmac_update()

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This loop is a bit hard to read, with the loop counter that's used in
the HMAC being separate from the actual loop counter, which counts
backwards for some reason.  Just replace it with a regular loop.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Eric Biggers 2026-04-19 23:34:22 -07:00 committed by Herbert Xu
parent 7cca456c3e
commit 58d0b2b907
1 changed files with 2 additions and 12 deletions
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14
crypto/drbg.c
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@ -137,11 +137,6 @@ struct drbg_state {
size_t test_entropylen;
};
enum drbg_prefixes {
DRBG_PREFIX0 = 0x00,
DRBG_PREFIX1,
};
/******************************************************************
* HMAC DRBG functions
******************************************************************/
@ -151,19 +146,14 @@ static void drbg_hmac_update(struct drbg_state *drbg,
const u8 *data1, size_t data1_len,
const u8 *data2, size_t data2_len)
{
int i = 0;
struct hmac_sha512_ctx hmac_ctx;
u8 new_key[DRBG_STATE_LEN];
for (i = 2; 0 < i; i--) {
/* first round uses 0x0, second 0x1 */
unsigned char prefix = DRBG_PREFIX0;
if (1 == i)
prefix = DRBG_PREFIX1;
for (u8 i = 0; i < 2; i++) {
/* 10.1.2.2 step 1 and 4 -- concatenation and HMAC for key */
hmac_sha512_init(&hmac_ctx, &drbg->key);
hmac_sha512_update(&hmac_ctx, drbg->V, DRBG_STATE_LEN);
hmac_sha512_update(&hmac_ctx, &prefix, 1);
hmac_sha512_update(&hmac_ctx, &i, 1);
hmac_sha512_update(&hmac_ctx, data1, data1_len);
hmac_sha512_update(&hmac_ctx, data2, data2_len);
hmac_sha512_final(&hmac_ctx, new_key);