Moving transcript and PRF functions to SSL_TRANSCRIPT.

Change-Id: I98903df561bbf8c5739f892d2ad5e89ac0eb8e6f
Reviewed-on: https://boringssl-review.googlesource.com/13369
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/ssl/ssl_session.c b/ssl/ssl_session.c
index 9221e92..908d5dc 100644
--- a/ssl/ssl_session.c
+++ b/ssl/ssl_session.c
@@ -494,6 +494,16 @@
   return CRYPTO_get_ex_data(&session->ex_data, idx);
 }
 
+const EVP_MD *SSL_SESSION_get_digest(const SSL_SESSION *session,
+                                     const SSL *ssl) {
+  uint16_t version;
+  if (!ssl->method->version_from_wire(&version, session->ssl_version)) {
+    return NULL;
+  }
+
+  return ssl_get_handshake_digest(session->cipher->algorithm_prf, version);
+}
+
 int ssl_get_new_session(SSL_HANDSHAKE *hs, int is_server) {
   SSL *const ssl = hs->ssl;
   if (ssl->mode & SSL_MODE_NO_SESSION_CREATION) {