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Mitigate triple handshake attack by comparing digests only

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This paves the way for the removal of the peer CRT chain from
`mbedtls_ssl_session`.
This commit is contained in:
Hanno Becker 2019-02-05 17:02:46 +00:00
parent 3008d2869f
commit df75938b84
1 changed files with 31 additions and 0 deletions
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31
library/ssl_tls.c
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@ -6139,6 +6139,8 @@ write_msg:
}
#if defined(MBEDTLS_SSL_RENEGOTIATION) && defined(MBEDTLS_SSL_CLI_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
unsigned char *crt_buf,
size_t crt_buf_len )
@ -6153,6 +6155,35 @@ static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
return( memcmp( peer_crt->raw.p, crt_buf, crt_buf_len ) );
}
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
unsigned char *crt_buf,
size_t crt_buf_len )
{
int ret;
unsigned char const * const peer_cert_digest =
ssl->session->peer_cert_digest;
mbedtls_md_type_t const peer_cert_digest_type =
ssl->session->peer_cert_digest_type;
mbedtls_md_info_t const * const digest_info =
mbedtls_md_info_from_type( peer_cert_digest_type );
unsigned char tmp_digest[MBEDTLS_SSL_PEER_CERT_DIGEST_MAX_LEN];
size_t digest_len;
if( peer_cert_digest == NULL || digest_info == NULL )
return( -1 );
digest_len = mbedtls_md_get_size( digest_info );
if( digest_len > MBEDTLS_SSL_PEER_CERT_DIGEST_MAX_LEN )
return( -1 );
ret = mbedtls_md( digest_info, crt_buf, crt_buf_len, tmp_digest );
if( ret != 0 )
return( -1 );
return( memcmp( tmp_digest, peer_cert_digest, digest_len ) );
}
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_SSL_RENEGOTIATION && MBEDTLS_SSL_CLI_C */
static void ssl_clear_peer_cert( mbedtls_ssl_session *session )