#define SSL_SOME_MODES_USE_MAC
#endif
+/* The function below is only used in the Lucky 13 counter-measure in
+ * ssl_decrypt_buf(). These are the defines that guard the call site. */
+#if defined(SSL_SOME_MODES_USE_MAC) && \
+ ( defined(MBEDTLS_SSL_PROTO_TLS1) || \
+ defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+ defined(MBEDTLS_SSL_PROTO_TLS1_2) )
+/* This function makes sure every byte in the memory region is accessed
+ * (in ascending addresses order) */
+static void ssl_read_memory( unsigned char *p, size_t len )
+{
+ unsigned char acc = 0;
+ volatile unsigned char force;
+
+ for( ; len != 0; p++, len-- )
+ acc ^= *p;
+
+ force = acc;
+ (void) force;
+}
+#endif /* SSL_SOME_MODES_USE_MAC && ( TLS1 || TLS1_1 || TLS1_2 ) */
+
/*
* Encryption/decryption functions
*/
defined(MBEDTLS_SSL_PROTO_TLS1_2)
if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_1 )
{
+ unsigned char mac[MBEDTLS_SSL_MAC_ADD];
+
mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc, ssl->out_ctr, 8 );
mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc, ssl->out_hdr, 3 );
mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc, ssl->out_len, 2 );
mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc,
ssl->out_msg, ssl->out_msglen );
- mbedtls_md_hmac_finish( &ssl->transform_out->md_ctx_enc,
- ssl->out_msg + ssl->out_msglen );
+ mbedtls_md_hmac_finish( &ssl->transform_out->md_ctx_enc, mac );
mbedtls_md_hmac_reset( &ssl->transform_out->md_ctx_enc );
+
+ memcpy( ssl->out_msg + ssl->out_msglen, mac, ssl->transform_out->maclen );
}
else
#endif
return( 0 );
}
-#define SSL_MAX_MAC_SIZE 48
-
static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
{
size_t i;
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
if( ssl->session_in->encrypt_then_mac == MBEDTLS_SSL_ETM_ENABLED )
{
- unsigned char computed_mac[SSL_MAX_MAC_SIZE];
+ unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD];
unsigned char pseudo_hdr[13];
MBEDTLS_SSL_DEBUG_MSG( 3, ( "using encrypt then mac" ) );
mbedtls_md_hmac_update( &ssl->transform_in->md_ctx_dec, pseudo_hdr, 13 );
mbedtls_md_hmac_update( &ssl->transform_in->md_ctx_dec,
ssl->in_iv, ssl->in_msglen );
- mbedtls_md_hmac_finish( &ssl->transform_in->md_ctx_dec, computed_mac );
+ mbedtls_md_hmac_finish( &ssl->transform_in->md_ctx_dec, mac_expect );
mbedtls_md_hmac_reset( &ssl->transform_in->md_ctx_dec );
MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", ssl->in_iv + ssl->in_msglen,
ssl->transform_in->maclen );
- MBEDTLS_SSL_DEBUG_BUF( 4, "computed mac", computed_mac,
+ MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect,
ssl->transform_in->maclen );
- if( mbedtls_ssl_safer_memcmp( ssl->in_iv + ssl->in_msglen, computed_mac,
- ssl->transform_in->maclen ) != 0 )
+ if( mbedtls_ssl_safer_memcmp( ssl->in_iv + ssl->in_msglen, mac_expect,
+ ssl->transform_in->maclen ) != 0 )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "message mac does not match" ) );
#if defined(SSL_SOME_MODES_USE_MAC)
if( auth_done == 0 )
{
- unsigned char tmp[SSL_MAX_MAC_SIZE];
+ unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD];
ssl->in_msglen -= ssl->transform_in->maclen;
ssl->in_len[0] = (unsigned char)( ssl->in_msglen >> 8 );
ssl->in_len[1] = (unsigned char)( ssl->in_msglen );
- memcpy( tmp, ssl->in_msg + ssl->in_msglen, ssl->transform_in->maclen );
-
#if defined(MBEDTLS_SSL_PROTO_SSL3)
if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
{
{
/*
* Process MAC and always update for padlen afterwards to make
- * total time independent of padlen
- *
- * extra_run compensates MAC check for padlen
+ * total time independent of padlen.
*
* Known timing attacks:
* - Lucky Thirteen (http://www.isg.rhul.ac.uk/tls/TLStiming.pdf)
*
- * We use ( ( Lx + 8 ) / 64 ) to handle 'negative Lx' values
- * correctly. (We round down instead of up, so -56 is the correct
- * value for our calculations instead of -55)
+ * To compensate for different timings for the MAC calculation
+ * depending on how much padding was removed (which is determined
+ * by padlen), process extra_run more blocks through the hash
+ * function.
+ *
+ * The formula in the paper is
+ * extra_run = ceil( (L1-55) / 64 ) - ceil( (L2-55) / 64 )
+ * where L1 is the size of the header plus the decrypted message
+ * plus CBC padding and L2 is the size of the header plus the
+ * decrypted message. This is for an underlying hash function
+ * with 64-byte blocks.
+ * We use ( (Lx+8) / 64 ) to handle 'negative Lx' values
+ * correctly. We round down instead of up, so -56 is the correct
+ * value for our calculations instead of -55.
+ *
+ * Repeat the formula rather than defining a block_size variable.
+ * This avoids requiring division by a variable at runtime
+ * (which would be marginally less efficient and would require
+ * linking an extra division function in some builds).
*/
size_t j, extra_run = 0;
- extra_run = ( 13 + ssl->in_msglen + padlen + 8 ) / 64 -
- ( 13 + ssl->in_msglen + 8 ) / 64;
+
+ /*
+ * The next two sizes are the minimum and maximum values of
+ * in_msglen over all padlen values.
+ *
+ * They're independent of padlen, since we previously did
+ * in_msglen -= padlen.
+ *
+ * Note that max_len + maclen is never more than the buffer
+ * length, as we previously did in_msglen -= maclen too.
+ */
+ const size_t max_len = ssl->in_msglen + padlen;
+ const size_t min_len = ( max_len > 256 ) ? max_len - 256 : 0;
+
+ switch( ssl->transform_in->ciphersuite_info->mac )
+ {
+#if defined(MBEDTLS_MD5_C) || defined(MBEDTLS_SHA1_C) || \
+ defined(MBEDTLS_SHA256_C)
+ case MBEDTLS_MD_MD5:
+ case MBEDTLS_MD_SHA1:
+ case MBEDTLS_MD_SHA256:
+ /* 8 bytes of message size, 64-byte compression blocks */
+ extra_run = ( 13 + ssl->in_msglen + padlen + 8 ) / 64 -
+ ( 13 + ssl->in_msglen + 8 ) / 64;
+ break;
+#endif
+#if defined(MBEDTLS_SHA512_C)
+ case MBEDTLS_MD_SHA384:
+ /* 16 bytes of message size, 128-byte compression blocks */
+ extra_run = ( 13 + ssl->in_msglen + padlen + 16 ) / 128 -
+ ( 13 + ssl->in_msglen + 16 ) / 128;
+ break;
+#endif
+ default:
+ MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+ return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+ }
extra_run &= correct * 0xFF;
mbedtls_md_hmac_update( &ssl->transform_in->md_ctx_dec, ssl->in_len, 2 );
mbedtls_md_hmac_update( &ssl->transform_in->md_ctx_dec, ssl->in_msg,
ssl->in_msglen );
- mbedtls_md_hmac_finish( &ssl->transform_in->md_ctx_dec,
- ssl->in_msg + ssl->in_msglen );
- /* Call mbedtls_md_process at least once due to cache attacks */
+ /* Make sure we access everything even when padlen > 0. This
+ * makes the synchronisation requirements for just-in-time
+ * Prime+Probe attacks much tighter and hopefully impractical. */
+ ssl_read_memory( ssl->in_msg + ssl->in_msglen, padlen );
+ mbedtls_md_hmac_finish( &ssl->transform_in->md_ctx_dec, mac_expect );
+
+ /* Call mbedtls_md_process at least once due to cache attacks
+ * that observe whether md_process() was called of not */
for( j = 0; j < extra_run + 1; j++ )
mbedtls_md_process( &ssl->transform_in->md_ctx_dec, ssl->in_msg );
mbedtls_md_hmac_reset( &ssl->transform_in->md_ctx_dec );
+
+ /* Make sure we access all the memory that could contain the MAC,
+ * before we check it in the next code block. This makes the
+ * synchronisation requirements for just-in-time Prime+Probe
+ * attacks much tighter and hopefully impractical. */
+ ssl_read_memory( ssl->in_msg + min_len,
+ max_len - min_len + ssl->transform_in->maclen );
}
else
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
- MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", tmp, ssl->transform_in->maclen );
- MBEDTLS_SSL_DEBUG_BUF( 4, "computed mac", ssl->in_msg + ssl->in_msglen,
- ssl->transform_in->maclen );
+#if defined(MBEDTLS_SSL_DEBUG_ALL)
+ MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect, ssl->transform_in->maclen );
+ MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", ssl->in_msg + ssl->in_msglen,
+ ssl->transform_in->maclen );
+#endif
- if( mbedtls_ssl_safer_memcmp( tmp, ssl->in_msg + ssl->in_msglen,
- ssl->transform_in->maclen ) != 0 )
+ if( mbedtls_ssl_safer_memcmp( ssl->in_msg + ssl->in_msglen, mac_expect,
+ ssl->transform_in->maclen ) != 0 )
{
#if defined(MBEDTLS_SSL_DEBUG_ALL)
MBEDTLS_SSL_DEBUG_MSG( 1, ( "message mac does not match" ) );
projects / platform / upstream / iotivity.git / blobdiff