crypto: drbg - Clean up loop in drbg_hmac_update()

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>

diff --git a/crypto/drbg.c b/crypto/drbg.c
index b54c807930af88675fe9cebcdb8357c774bd042a..ad7b9577479e0a68f3276657e0436d5ab89c47b1 100644 (file)
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -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);