Add handshake message writing variant that doesn't update checksum
The helper `mbedtls_ssl_write_handshake_msg` writes a handshake message
and updates the handshake transcript.
With TLS 1.3, we need finer control over the checksum: updating
at message granularity is not sufficient. To allow for manual maintenance
of the checksum in those cases, refine `mbedtls_ssl_write_handshake_msg()`
into `mbedtls_ssl_write_handshake_msg_ext()` which takes a parameter
determining whether the checksum should be updated.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index cc19f47..e4966f0 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -971,7 +971,13 @@
unsigned update_hs_digest );
int mbedtls_ssl_fetch_input( mbedtls_ssl_context *ssl, size_t nb_want );
-int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_write_handshake_msg_ext( mbedtls_ssl_context *ssl,
+ int update_checksum );
+static inline int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl )
+{
+ return( mbedtls_ssl_write_handshake_msg_ext( ssl, 1 /* update checksum */ ) );
+}
+
int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, uint8_t force_flush );
int mbedtls_ssl_flush_output( mbedtls_ssl_context *ssl );
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 76cc2b1..fe26eaa 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -2360,7 +2360,8 @@
* (including handshake headers but excluding record headers)
* - ssl->out_msg: the record contents (handshake headers + content)
*/
-int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl )
+int mbedtls_ssl_write_handshake_msg_ext( mbedtls_ssl_context *ssl,
+ int update_checksum )
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
const size_t hs_len = ssl->out_msglen - 4;
@@ -2469,7 +2470,7 @@
#endif /* MBEDTLS_SSL_PROTO_DTLS */
/* Update running hashes of handshake messages seen */
- if( hs_type != MBEDTLS_SSL_HS_HELLO_REQUEST )
+ if( hs_type != MBEDTLS_SSL_HS_HELLO_REQUEST && update_checksum != 0 )
ssl->handshake->update_checksum( ssl, ssl->out_msg, ssl->out_msglen );
}
