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Do not encrypt CCS records

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According to the TLS 1.3 standard the CCS records must be unencrypted.

When a record is not encrypted the counter, used in the dynamic IV
creation, is not incremented.

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
This commit is contained in:
Gabor Mezei 2022-06-22 13:17:28 +02:00
parent 7e2dbafe2d
commit 96ec831385
No known key found for this signature in database
GPG key ID: 08AB7BB35012F877
3 changed files with 30 additions and 17 deletions
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3
library/ssl_misc.h
View file

@ -1271,7 +1271,8 @@ static inline int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl )
int mbedtls_ssl_finish_handshake_msg( mbedtls_ssl_context *ssl,
size_t buf_len, size_t msg_len );
int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, int force_flush );
int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, int force_flush,
int encrypt );
int mbedtls_ssl_flush_output( mbedtls_ssl_context *ssl );
int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl );

42
library/ssl_msg.c
View file

@ -151,6 +151,9 @@ exit:
#define SSL_DONT_FORCE_FLUSH 0
#define SSL_FORCE_FLUSH 1
#define SSL_DONT_ENCRYPT_RECORD 0
#define SSL_ENCRYPT_RECORD 1
#if defined(MBEDTLS_SSL_PROTO_DTLS)
/* Forward declarations for functions related to message buffering. */
@ -2324,7 +2327,8 @@ int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
}
/* Actually send the message out */
if( ( ret = mbedtls_ssl_write_record( ssl, force_flush ) ) != 0 )
if( ( ret = mbedtls_ssl_write_record( ssl, force_flush,
SSL_ENCRYPT_RECORD ) ) != 0 )
{
MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
return( ret );
@ -2570,7 +2574,8 @@ int mbedtls_ssl_write_handshake_msg_ext( mbedtls_ssl_context *ssl,
else
#endif
{
if( ( ret = mbedtls_ssl_write_record( ssl, force_flush ) ) != 0 )
if( ( ret = mbedtls_ssl_write_record( ssl, force_flush,
SSL_ENCRYPT_RECORD ) ) != 0 )
{
MBEDTLS_SSL_DEBUG_RET( 1, "ssl_write_record", ret );
return( ret );
@ -2610,7 +2615,8 @@ cleanup:
* - ssl->out_msglen: length of the record content (excl headers)
* - ssl->out_msg: record content
*/
int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, int force_flush )
int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, int force_flush,
int encrypt )
{
int ret, done = 0;
size_t len = ssl->out_msglen;
@ -2642,7 +2648,7 @@ int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, int force_flush )
memcpy( ssl->out_ctr, ssl->cur_out_ctr, MBEDTLS_SSL_SEQUENCE_NUMBER_LEN );
MBEDTLS_PUT_UINT16_BE( len, ssl->out_len, 0);
if( ssl->transform_out != NULL )
if( ssl->transform_out != NULL && encrypt )
{
mbedtls_record rec;
@ -2714,17 +2720,21 @@ int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, int force_flush )
ssl->out_left += protected_record_size;
ssl->out_hdr += protected_record_size;
mbedtls_ssl_update_out_pointers( ssl, ssl->transform_out );
mbedtls_ssl_update_out_pointers( ssl, encrypt ? ssl->transform_out : NULL );
for( i = 8; i > mbedtls_ssl_ep_len( ssl ); i-- )
if( ++ssl->cur_out_ctr[i - 1] != 0 )
break;
/* The loop goes to its end iff the counter is wrapping */
if( i == mbedtls_ssl_ep_len( ssl ) )
/* Do not increment the counter for CCS records. */
if( encrypt )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "outgoing message counter would wrap" ) );
return( MBEDTLS_ERR_SSL_COUNTER_WRAPPING );
for( i = 8; i > mbedtls_ssl_ep_len( ssl ); i-- )
if( ++ssl->cur_out_ctr[i - 1] != 0 )
break;
/* The loop goes to its end iff the counter is wrapping */
if( i == mbedtls_ssl_ep_len( ssl ) )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "outgoing message counter would wrap" ) );
return( MBEDTLS_ERR_SSL_COUNTER_WRAPPING );
}
}
}
@ -4812,7 +4822,8 @@ int mbedtls_ssl_send_alert_message( mbedtls_ssl_context *ssl,
ssl->out_msg[0] = level;
ssl->out_msg[1] = message;
if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH ) ) != 0 )
if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH,
SSL_ENCRYPT_RECORD ) ) != 0 )
{
MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
return( ret );
@ -5602,7 +5613,8 @@ static int ssl_write_real( mbedtls_ssl_context *ssl,
ssl->out_msgtype = MBEDTLS_SSL_MSG_APPLICATION_DATA;
memcpy( ssl->out_msg, buf, len );
if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH ) ) != 0 )
if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH,
SSL_ENCRYPT_RECORD ) ) != 0 )
{
MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
return( ret );

2
library/ssl_tls13_generic.c
View file

@ -1341,7 +1341,7 @@ int mbedtls_ssl_tls13_write_change_cipher_spec( mbedtls_ssl_context *ssl )
ssl->out_msgtype = MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC;
/* Dispatch message */
MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_record( ssl, 0 ) );
MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_record( ssl, 0, 0 ) );
cleanup: