Added support for out-of-band Pre-shared keys under TLS1.3

That adds support for pre-shared keys with and without Diffie-Hellman
key exchange. That's a modified version of initial Ander's patch.

Resolves #414
Resolves #125

Signed-off-by: Ander Juaristi <a@juaristi.eus>
Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.org>

1 files changed, 37 insertions, 5 deletions

diff --git a/lib/handshake-tls13.c b/lib/handshake-tls13.c
index edb6e80574..de14cf106e 100644
--- a/lib/handshake-tls13.c
+++ b/lib/handshake-tls13.c
@@ -204,14 +204,46 @@ static int generate_ap_traffic_keys(gnutls_session_t session)
 static int generate_hs_traffic_keys(gnutls_session_t session)
 {
 	int ret;
+	unsigned null_key = 0;
 
-	if (unlikely(session->key.key.size == 0 || session->key.proto.tls13.temp_secret_size == 0))
+	if (unlikely(session->key.proto.tls13.temp_secret_size == 0))
 		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 
-	ret = _tls13_update_secret(session, session->key.key.data, session->key.key.size);
-	if (ret < 0) {
-		gnutls_assert();
-		return ret;
+	if ((session->security_parameters.entity == GNUTLS_CLIENT &&
+	    !(session->internals.hsk_flags & HSK_KEY_SHARE_RECEIVED)) ||
+	    (session->security_parameters.entity == GNUTLS_SERVER &&
+	    !(session->internals.hsk_flags & HSK_KEY_SHARE_SENT))) {
+
+		if ((session->internals.hsk_flags & HSK_PSK_SELECTED) &&
+		    (session->internals.hsk_flags & HSK_PSK_KE_MODE_PSK)) {
+			null_key = 1;
+		}
+	}
+
+	if (null_key) {
+		uint8_t digest[MAX_HASH_SIZE];
+		unsigned digest_size;
+
+		if (unlikely(session->security_parameters.prf == NULL))
+			return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
+
+		digest_size = session->security_parameters.prf->output_size;
+		memset(digest, 0, digest_size);
+
+		ret = _tls13_update_secret(session, digest, digest_size);
+		if (ret < 0) {
+			gnutls_assert();
+			return ret;
+		}
+	} else {
+		if (unlikely(session->key.key.size == 0))
+			return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
+
+		ret = _tls13_update_secret(session, session->key.key.data, session->key.key.size);
+		if (ret < 0) {
+			gnutls_assert();
+			return ret;
+		}
 	}
 
 	ret = _tls13_connection_state_init(session, STAGE_HS);