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Add handshake message writing variant that doesn't update checksum

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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>
This commit is contained in:
Hanno Becker 2021-08-07 14:29:49 +01:00
parent 78f6f05778
commit f3cce8b0e1
2 changed files with 10 additions and 3 deletions
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8
library/ssl_misc.h
View file

@ -971,7 +971,13 @@ int mbedtls_ssl_read_record( mbedtls_ssl_context *ssl,
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 );

5
library/ssl_msg.c
View file

@ -2360,7 +2360,8 @@ void mbedtls_ssl_send_flight_completed( mbedtls_ssl_context *ssl )
* (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 @@ int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl )
#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 );
}