Improve some comments and internal documentation
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/ssl_invasive.h b/library/ssl_invasive.h
index 49ee83f..2a8d6b5 100644
--- a/library/ssl_invasive.h
+++ b/library/ssl_invasive.h
@@ -42,9 +42,11 @@
* max_data_len bytes from \p data.
*
* \param ctx The HMAC context. It must have keys configured
- * with mbedtls_md_hmac_starts(). It is reset using
- * mbedtls_md_hmac_reset() after the computation is
- * complete to prepare for the next computation.
+ * with mbedtls_md_hmac_starts() and use one of the
+ * following hashes: SHA-384, SHA-256, SHA-1 or MD-5.
+ * It is reset using mbedtls_md_hmac_reset() after
+ * the computation is complete to prepare for the
+ * next computation.
* \param add_data The additional data prepended to \p data. This
* must point to a readable buffer of \p add_data_len
* bytes.
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 086db88..3d6203c 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -1127,7 +1127,7 @@
* extension to the MD API in order to get constant-flow behaviour.
*
* HMAC(msg) is defined as HASH(okey + HASH(ikey + msg)) where + means
- * concatenation, and okey/ikey is the XOR of the key with some fix bit
+ * concatenation, and okey/ikey are the XOR of the key with some fixed bit
* patterns (see RFC 2104, sec. 2), which are stored in ctx->hmac_ctx.
*
* We'll first compute inner_hash = HASH(ikey + msg) by hashing up to
@@ -1137,6 +1137,8 @@
* Then we only need to compute HASH(okey + inner_hash) and we're done.
*/
const mbedtls_md_type_t md_alg = mbedtls_md_get_type( ctx->md_info );
+ /* TLS 1.0-1.2 only support SHA-384, SHA-256, SHA-1, MD-5,
+ * all of which have the same block size except SHA-384. */
const size_t block_size = md_alg == MBEDTLS_MD_SHA384 ? 128 : 64;
const unsigned char * const ikey = (unsigned char *) ctx->hmac_ctx;
const unsigned char * const okey = ikey + block_size;