Improve documentation of ssl_populate_transform()
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index fd0c8a7..116d2a2 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -973,9 +973,12 @@
transform->taglen =
ciphersuite_info->flags & MBEDTLS_CIPHERSUITE_SHORT_TAG ? 8 : 16;
- /* All modes haves 96-bit IVs;
- * GCM and CCM has 4 implicit and 8 explicit bytes
- * ChachaPoly has all 12 bytes implicit
+ /* All modes haves 96-bit IVs, but the length of the static parts vary
+ * with mode and version:
+ * - For GCM and CCM in TLS 1.2, there's a static IV of 4 Bytes
+ * (to be concatenated with a dynamically chosen IV of 8 Bytes)
+ * - For ChaChaPoly in TLS 1.2, there's a static IV of 12 Bytes
+ * (to be XOR'ed with the 8 Byte record sequence number).
*/
transform->ivlen = 12;
if( cipher_info->mode == MBEDTLS_MODE_CHACHAPOLY )