Remember suitable hash function for any signature algorithm.
This commit changes `ssl_parse_signature_algorithms_ext` to remember one suitable ( := supported by client and by our config ) hash algorithm per signature algorithm. It also modifies the ciphersuite checking function `ssl_ciphersuite_match` to refuse a suite if there is no suitable hash algorithm. Finally, it adds the corresponding entry to the ChangeLog.
This commit is contained in:
Hanno Becker
parent
1aa267cbc3
commit
7e5437a972
7 changed files with 307 additions and 33 deletions
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@ -186,15 +186,30 @@ static int ssl_parse_renegotiation_info( mbedtls_ssl_context *ssl,
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#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
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defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
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/*
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* Status of the implementation of signature-algorithms extension:
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*
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* Currently, we are only considering the signature-algorithm extension
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* to pick a ciphersuite which allows us to send the ServerKeyExchange
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* message with a signature-hash combination that the user allows.
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*
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* We do *not* check whether all certificates in our certificate
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* chain are signed with an allowed signature-hash pair.
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* This needs to be done at a later stage.
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*
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*/
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static int ssl_parse_signature_algorithms_ext( mbedtls_ssl_context *ssl,
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const unsigned char *buf,
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size_t len )
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{
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size_t sig_alg_list_size;
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const unsigned char *p;
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const unsigned char *end = buf + len;
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const int *md_cur;
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mbedtls_md_type_t md_cur;
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mbedtls_pk_type_t sig_cur;
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sig_alg_list_size = ( ( buf[0] << 8 ) | ( buf[1] ) );
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if( sig_alg_list_size + 2 != len ||
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@ -204,29 +219,48 @@ static int ssl_parse_signature_algorithms_ext( mbedtls_ssl_context *ssl,
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return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
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}
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/*
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* For now, ignore the SignatureAlgorithm part and rely on offered
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* ciphersuites only for that part. To be fixed later.
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/* Currently we only guarantee signing the ServerKeyExchange message according
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* to the constraints specified in this extension (see above), so it suffices
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* to remember only one suitable hash for each possible signature algorithm.
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*
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* So, just look at the HashAlgorithm part.
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* This will change when we also consider certificate signatures,
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* in which case we will need to remember the whole signature-hash
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* pair list from the extension.
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*/
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for( md_cur = ssl->conf->sig_hashes; *md_cur != MBEDTLS_MD_NONE; md_cur++ ) {
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for( p = buf + 2; p < end; p += 2 ) {
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if( *md_cur == (int) mbedtls_ssl_md_alg_from_hash( p[0] ) ) {
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ssl->handshake->sig_alg = p[0];
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goto have_sig_alg;
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}
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for( p = buf + 2; p < end; p += 2 )
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{
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/* Silently ignore unknown signature or hash algorithms. */
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if( ( sig_cur = mbedtls_ssl_pk_alg_from_sig( p[1] ) ) == MBEDTLS_PK_NONE )
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{
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: unknown sig alg encoding %d",
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p[1] ) );
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continue;
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}
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/* Check if we support the hash the user proposes */
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md_cur = mbedtls_ssl_md_alg_from_hash( p[0] );
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if( md_cur == MBEDTLS_MD_NONE )
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{
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: unknown hash alg encoding %d",
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p[0] ) );
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continue;
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}
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if( mbedtls_ssl_check_sig_hash( ssl, md_cur ) == 0 )
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{
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mbedtls_ssl_sig_hash_set_add( &ssl->handshake->hash_algs, sig_cur, md_cur );
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: match sig %d and hash %d",
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sig_cur, md_cur ) );
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}
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else
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{
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: hash alg %d not supported",
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md_cur ) );
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}
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}
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/* Some key echanges do not need signatures at all */
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "no signature_algorithm in common" ) );
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return( 0 );
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have_sig_alg:
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: %d",
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ssl->handshake->sig_alg ) );
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return( 0 );
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}
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#endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
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@ -710,6 +744,11 @@ static int ssl_ciphersuite_match( mbedtls_ssl_context *ssl, int suite_id,
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{
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const mbedtls_ssl_ciphersuite_t *suite_info;
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#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
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defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
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mbedtls_pk_type_t sig_type;
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#endif
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suite_info = mbedtls_ssl_ciphersuite_from_id( suite_id );
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if( suite_info == NULL )
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{
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@ -776,6 +815,25 @@ static int ssl_ciphersuite_match( mbedtls_ssl_context *ssl, int suite_id,
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}
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#endif
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#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
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defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
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/* If the ciphersuite requires signing, check whether
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* a suitable hash algorithm is present. */
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if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
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{
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sig_type = mbedtls_ssl_get_ciphersuite_sig_alg( suite_info );
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if( sig_type != MBEDTLS_PK_NONE &&
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mbedtls_ssl_sig_hash_set_find( &ssl->handshake->hash_algs, sig_type ) == MBEDTLS_MD_NONE )
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{
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: no suitable hash algorithm "
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"for signature algorithm %d", sig_type ) );
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return( 0 );
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}
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}
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#endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
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MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED */
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#if defined(MBEDTLS_X509_CRT_PARSE_C)
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/*
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* Final check: if ciphersuite requires us to have a
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@ -1085,6 +1143,15 @@ static int ssl_parse_client_hello( mbedtls_ssl_context *ssl )
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const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
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int major, minor;
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/* If there is no signature-algorithm extension present,
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* we need to fall back to the default values for allowed
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* signature-hash pairs. */
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#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
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defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
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int sig_hash_alg_ext_present = 0;
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#endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
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MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED */
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MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse client hello" ) );
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#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
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@ -1582,10 +1649,11 @@ read_record_header:
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if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
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break;
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#endif
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ret = ssl_parse_signature_algorithms_ext( ssl, ext + 4, ext_size );
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if( ret != 0 )
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return( ret );
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sig_hash_alg_ext_present = 1;
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break;
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#endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
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MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED */
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@ -1722,6 +1790,26 @@ read_record_header:
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}
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#endif /* MBEDTLS_SSL_FALLBACK_SCSV */
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#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
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defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
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/*
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* Try to fall back to default hash SHA1 if the client
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* hasn't provided any preferred signature-hash combinations.
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*/
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if( sig_hash_alg_ext_present == 0 )
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{
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mbedtls_md_type_t md_default = MBEDTLS_MD_SHA1;
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if( mbedtls_ssl_check_sig_hash( ssl, md_default ) != 0 )
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md_default = MBEDTLS_MD_NONE;
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mbedtls_ssl_sig_hash_set_const_hash( &ssl->handshake->hash_algs, md_default );
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}
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#endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
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MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED */
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/*
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* Check for TLS_EMPTY_RENEGOTIATION_INFO_SCSV
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*/
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@ -1847,6 +1935,28 @@ have_ciphersuite:
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mbedtls_ssl_recv_flight_completed( ssl );
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#endif
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/* Debugging-only output for testsuite */
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#if defined(MBEDTLS_DEBUG_C) && \
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defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
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defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
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if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
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{
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mbedtls_pk_type_t sig_alg = mbedtls_ssl_get_ciphersuite_sig_alg( ciphersuite_info );
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if( sig_alg != MBEDTLS_PK_NONE )
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{
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mbedtls_md_type_t md_alg = mbedtls_ssl_sig_hash_set_find( &ssl->handshake->hash_algs,
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sig_alg );
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: %d",
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mbedtls_ssl_hash_from_md_alg( md_alg ) ) );
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}
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else
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{
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "no hash algorithm for signature algorithm %d - should not happen",
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sig_alg ) );
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}
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}
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#endif
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MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse client hello" ) );
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return( 0 );
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@ -2669,7 +2779,7 @@ static int ssl_write_server_key_exchange( mbedtls_ssl_context *ssl )
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size_t n = 0;
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const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
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ssl->transform_negotiate->ciphersuite_info;
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#if defined(MBEDTLS_KEY_EXCHANGE__SOME_PFS__ENABLED)
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unsigned char *p = ssl->out_msg + 4;
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unsigned char *dig_signed = p;
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@ -2736,7 +2846,7 @@ static int ssl_write_server_key_exchange( mbedtls_ssl_context *ssl )
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#endif /* MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED ||
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MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
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/*
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/*
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* For DHE key exchanges, add the DH parameters here.
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*/
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#if defined(MBEDTLS_KEY_EXCHANGE__SOME__DHE_ENABLED)
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@ -2832,7 +2942,7 @@ curve_matching_done:
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return( ret );
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}
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dig_signed = p;
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dig_signed = p;
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dig_signed_len = len;
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p += len;
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@ -2852,19 +2962,29 @@ curve_matching_done:
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size_t signature_len = 0;
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unsigned int hashlen = 0;
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unsigned char hash[64];
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mbedtls_md_type_t md_alg = MBEDTLS_MD_NONE;
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/*
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* Choose hash algorithm. NONE means MD5 + SHA1 here.
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* Choose hash algorithm:
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* - For TLS 1.2, obey signature-hash-algorithm extension to choose appropriate hash.
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* - For SSL3, TLS1.0, TLS1.1 and ECDHE_ECDSA, use SHA1 (RFC 4492, Sec. 5.4)
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* - Otherwise, use MD5 + SHA1 (RFC 4346, Sec. 7.4.3)
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*/
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mbedtls_md_type_t md_alg;
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#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
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mbedtls_pk_type_t sig_alg = mbedtls_ssl_get_ciphersuite_sig_pk_alg( ciphersuite_info );
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if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
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{
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md_alg = mbedtls_ssl_md_alg_from_hash( ssl->handshake->sig_alg );
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/* For TLS 1.2, obey signature-hash-algorithm extension
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* (RFC 5246, Sec. 7.4.1.4.1). */
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if( md_alg == MBEDTLS_MD_NONE )
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if( sig_alg == MBEDTLS_PK_NONE ||
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( md_alg = mbedtls_ssl_sig_hash_set_find( &ssl->handshake->hash_algs, sig_alg ) ) == MBEDTLS_MD_NONE )
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{
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
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/* (... because we choose a cipher suite
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* only if there is a matching hash.) */
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return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
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}
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}
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@ -2884,6 +3004,8 @@ curve_matching_done:
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md_alg = MBEDTLS_MD_NONE;
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}
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "pick hash algorithm %d for signing", md_alg ) );
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/*
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* Compute the hash to be signed
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*/
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@ -2971,7 +3093,7 @@ curve_matching_done:
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(unsigned int) ( mbedtls_md_get_size( mbedtls_md_info_from_type( md_alg ) ) ) );
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/*
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* Make the signature
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* Compute and add the signature
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*/
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if( mbedtls_ssl_own_key( ssl ) == NULL )
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{
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@ -2982,8 +3104,23 @@ curve_matching_done:
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#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
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if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
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{
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*(p++) = ssl->handshake->sig_alg;
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*(p++) = mbedtls_ssl_sig_from_pk( mbedtls_ssl_own_key( ssl ) );
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/* For TLS 1.2, we need to specify signature and hash algorithm
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* explicitly through a prefix to the signature.
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*
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* struct {
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* HashAlgorithm hash;
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* SignatureAlgorithm signature;
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* } SignatureAndHashAlgorithm;
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*
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* struct {
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* SignatureAndHashAlgorithm algorithm;
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* opaque signature<0..2^16-1>;
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* } DigitallySigned;
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*
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*/
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*(p++) = mbedtls_ssl_hash_from_md_alg( md_alg );
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*(p++) = mbedtls_ssl_sig_from_pk_alg( sig_alg );
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n += 2;
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}
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