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Use temporary buffer to hold the peer's HMAC

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This paves the way for a constant-flow implementation of HMAC checking, by
making sure that the comparison happens at a constant address. The missing
step is obviously to copy the HMAC from the secret offset to this temporary
buffer with constant flow, which will be done in the next few commits.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
This commit is contained in:
Manuel Pégourié-Gonnard 2020-08-13 12:08:54 +02:00
parent 71f4fa13bb
commit 3c31afaca6
1 changed files with 5 additions and 2 deletions
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7
library/ssl_msg.c
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@ -1637,6 +1637,7 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
if( auth_done == 0 ) if( auth_done == 0 )
{ {
unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD]; unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD];
unsigned char mac_peer[MBEDTLS_SSL_MAC_ADD];
/* If the initial value of padlen was such that /* If the initial value of padlen was such that
* data_len < maclen + padlen + 1, then padlen * data_len < maclen + padlen + 1, then padlen
@ -1663,6 +1664,7 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
data, rec->data_len, data, rec->data_len,
rec->ctr, rec->type, rec->ctr, rec->type,
mac_expect ); mac_expect );
memcpy( mac_peer, data + rec->data_len, transform->maclen );
} }
else else
#endif /* MBEDTLS_SSL_PROTO_SSL3 */ #endif /* MBEDTLS_SSL_PROTO_SSL3 */
@ -1699,6 +1701,7 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
* attacks much tighter and hopefully impractical. */ * attacks much tighter and hopefully impractical. */
ssl_read_memory( data + min_len, ssl_read_memory( data + min_len,
max_len - min_len + transform->maclen ); max_len - min_len + transform->maclen );
memcpy( mac_peer, data + rec->data_len, transform->maclen );
} }
else else
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \ #endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
@ -1710,10 +1713,10 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
#if defined(MBEDTLS_SSL_DEBUG_ALL) #if defined(MBEDTLS_SSL_DEBUG_ALL)
MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect, transform->maclen ); MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect, transform->maclen );
MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", data + rec->data_len, transform->maclen ); MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", mac_peer, transform->maclen );
#endif #endif
if( mbedtls_ssl_safer_memcmp( data + rec->data_len, mac_expect, if( mbedtls_ssl_safer_memcmp( mac_peer, mac_expect,
transform->maclen ) != 0 ) transform->maclen ) != 0 )
{ {
#if defined(MBEDTLS_SSL_DEBUG_ALL) #if defined(MBEDTLS_SSL_DEBUG_ALL)