commit 871fff076bacb3a0b57dafebe734892f06c893aa
author David Benjamin <davidben@chromium.org> Sun Dec 06 21:04:36 2015 -0500
committer Adam Langley <agl@google.com> Wed Dec 16 19:46:57 2015 +0000
tree 4605e5142edfeead2c45d5dc9f41f063ecd6c954
parent d9f0671bbe6a910c5be9888b5419ab5560dc56b7

*_Update of length zero is legal.

We can slightly simplify tls1_P_hash. (Confirmed md32_common.h emits
code with the check.)

Change-Id: I0293ceaaee261a7ac775b42a639f7a9f67705456
Reviewed-on: https://boringssl-review.googlesource.com/6647
Reviewed-by: Adam Langley <agl@google.com>

ssl/t1_enc.c

diff --git a/ssl/t1_enc.c b/ssl/t1_enc.c
index 8119025..bda7c5b 100644
--- a/ssl/t1_enc.c
+++ b/ssl/t1_enc.c
@@ -159,40 +159,36 @@
                        const uint8_t *seed1, size_t seed1_len,
                        const uint8_t *seed2, size_t seed2_len,
                        const uint8_t *seed3, size_t seed3_len) {
-  size_t chunk;
   HMAC_CTX ctx, ctx_tmp, ctx_init;
   uint8_t A1[EVP_MAX_MD_SIZE];
   unsigned A1_len;
   int ret = 0;
 
-  chunk = EVP_MD_size(md);
+  size_t chunk = EVP_MD_size(md);
 
   HMAC_CTX_init(&ctx);
   HMAC_CTX_init(&ctx_tmp);
   HMAC_CTX_init(&ctx_init);
   if (!HMAC_Init_ex(&ctx_init, secret, secret_len, md, NULL) ||
       !HMAC_CTX_copy_ex(&ctx, &ctx_init) ||
-      (seed1_len && !HMAC_Update(&ctx, seed1, seed1_len)) ||
-      (seed2_len && !HMAC_Update(&ctx, seed2, seed2_len)) ||
-      (seed3_len && !HMAC_Update(&ctx, seed3, seed3_len)) ||
+      !HMAC_Update(&ctx, seed1, seed1_len) ||
+      !HMAC_Update(&ctx, seed2, seed2_len) ||
+      !HMAC_Update(&ctx, seed3, seed3_len) ||
       !HMAC_Final(&ctx, A1, &A1_len)) {
     goto err;
   }
 
   for (;;) {
-    /* Reinit mac contexts. */
-    if (!HMAC_CTX_copy_ex(&ctx, &ctx_init) ||
-        !HMAC_Update(&ctx, A1, A1_len) ||
-        (out_len > chunk && !HMAC_CTX_copy_ex(&ctx_tmp, &ctx)) ||
-        (seed1_len && !HMAC_Update(&ctx, seed1, seed1_len)) ||
-        (seed2_len && !HMAC_Update(&ctx, seed2, seed2_len)) ||
-        (seed3_len && !HMAC_Update(&ctx, seed3, seed3_len))) {
-      goto err;
-    }
-
     unsigned len;
     uint8_t hmac[EVP_MAX_MD_SIZE];
-    if (!HMAC_Final(&ctx, hmac, &len)) {
+    if (!HMAC_CTX_copy_ex(&ctx, &ctx_init) ||
+        !HMAC_Update(&ctx, A1, A1_len) ||
+        /* Save a copy of |ctx| to compute the next A1 value below. */
+        (out_len > chunk && !HMAC_CTX_copy_ex(&ctx_tmp, &ctx)) ||
+        !HMAC_Update(&ctx, seed1, seed1_len) ||
+        !HMAC_Update(&ctx, seed2, seed2_len) ||
+        !HMAC_Update(&ctx, seed3, seed3_len) ||
+        !HMAC_Final(&ctx, hmac, &len)) {
       goto err;
     }
     assert(len == chunk);