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tls13: server: Add sig alg checks when selecting best certificate

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When selecting the server certificate based on
the signature algorithms supported by the client,
check the signature algorithms as close as possible
to the way they are checked to compute the
signature for the server to prove it possesses
the private key associated to the certificate.

That way we minimize the odds of selecting a
certificate for which the server will not be
able to compute the signature to prove it
possesses the private key associated to the
certificate.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
This commit is contained in:
Ronald Cron 2022-09-15 17:34:42 +02:00
parent c454aba203
commit 67ea2543ed
2 changed files with 52 additions and 7 deletions
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50
library/ssl_tls13_server.c
View file

@ -898,6 +898,34 @@ static int ssl_tls13_determine_key_exchange_mode( mbedtls_ssl_context *ssl )
#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
static psa_algorithm_t ssl_tls13_iana_sig_alg_to_psa_alg( uint16_t sig_alg )
{
switch( sig_alg )
{
case MBEDTLS_TLS1_3_SIG_ECDSA_SECP256R1_SHA256:
return( PSA_ALG_ECDSA( PSA_ALG_SHA_256 ) );
case MBEDTLS_TLS1_3_SIG_ECDSA_SECP384R1_SHA384:
return( PSA_ALG_ECDSA( PSA_ALG_SHA_384 ) );
case MBEDTLS_TLS1_3_SIG_ECDSA_SECP521R1_SHA512:
return( PSA_ALG_ECDSA( PSA_ALG_SHA_512 ) );
case MBEDTLS_TLS1_3_SIG_RSA_PSS_RSAE_SHA256:
return( PSA_ALG_RSA_PSS( PSA_ALG_SHA_256 ) );
case MBEDTLS_TLS1_3_SIG_RSA_PSS_RSAE_SHA384:
return( PSA_ALG_RSA_PSS( PSA_ALG_SHA_384 ) );
case MBEDTLS_TLS1_3_SIG_RSA_PSS_RSAE_SHA512:
return( PSA_ALG_RSA_PSS( PSA_ALG_SHA_512 ) );
case MBEDTLS_TLS1_3_SIG_RSA_PKCS1_SHA256:
case MBEDTLS_TLS1_3_SIG_RSA_PKCS1_SHA384:
case MBEDTLS_TLS1_3_SIG_RSA_PKCS1_SHA512:
return( PSA_ALG_RSA_PKCS1V15_CRYPT );
default:
return( PSA_ALG_NONE );
}
}
#endif /* MBEDTLS_USE_PSA_CRYPTO */
/*
* Pick best ( private key, certificate chain ) pair based on the signature
* algorithms supported by the client.
@ -923,9 +951,19 @@ static int ssl_tls13_pick_key_cert( mbedtls_ssl_context *ssl )
for( ; *sig_alg != MBEDTLS_TLS1_3_SIG_NONE; sig_alg++ )
{
if( !mbedtls_ssl_sig_alg_is_offered( ssl, *sig_alg ) )
continue;
if( !mbedtls_ssl_tls13_sig_alg_for_cert_verify_is_supported( *sig_alg ) )
continue;
for( key_cert = key_cert_list; key_cert != NULL;
key_cert = key_cert->next )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)
psa_algorithm_t psa_alg = PSA_ALG_NONE;
#endif /* MBEDTLS_USE_PSA_CRYPTO */
MBEDTLS_SSL_DEBUG_CRT( 3, "certificate (chain) candidate",
key_cert->cert );
@ -949,8 +987,18 @@ static int ssl_tls13_pick_key_cert( mbedtls_ssl_context *ssl )
"check signature algorithm %s [%04x]",
mbedtls_ssl_sig_alg_to_str( *sig_alg ),
*sig_alg ) );
#if defined(MBEDTLS_USE_PSA_CRYPTO)
psa_alg = ssl_tls13_iana_sig_alg_to_psa_alg( *sig_alg );
#endif /* MBEDTLS_USE_PSA_CRYPTO */
if( mbedtls_ssl_tls13_check_sig_alg_cert_key_match(
*sig_alg, &key_cert->cert->pk ) )
*sig_alg, &key_cert->cert->pk )
#if defined(MBEDTLS_USE_PSA_CRYPTO)
&& psa_alg != PSA_ALG_NONE &&
mbedtls_pk_can_do_ext( &key_cert->cert->pk, psa_alg,
PSA_KEY_USAGE_SIGN_HASH ) == 1
#endif /* MBEDTLS_USE_PSA_CRYPTO */
)
{
ssl->handshake->key_cert = key_cert;
MBEDTLS_SSL_DEBUG_MSG( 3,

9
tests/ssl-opt.sh
View file

@ -12671,8 +12671,7 @@ run_test "TLS 1.3: Check server no suitable signature algorithm, G->m" \
--x509certfile data_files/server2-sha256.crt --x509keyfile data_files/server2.key \
--priority=NORMAL:-SIGN-ALL:+SIGN-RSA-SHA512:+SIGN-RSA-PSS-RSAE-SHA512:+SIGN-ECDSA-SECP521R1-SHA512" \
1 \
-s "ssl_tls13_pick_key_cert:selected signature algorithm rsa_pss_rsae_sha512" \
-s "select_sig_alg_for_certificate_verify:no suitable signature algorithm found"
-S "ssl_tls13_pick_key_cert:check signature algorithm"
requires_openssl_tls1_3
requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3
@ -12688,8 +12687,7 @@ run_test "TLS 1.3: Check server no suitable signature algorithm, O->m" \
-cert data_files/server2-sha256.crt -key data_files/server2.key \
-sigalgs rsa_pkcs1_sha512:rsa_pss_rsae_sha512:ecdsa_secp521r1_sha512" \
1 \
-s "ssl_tls13_pick_key_cert:selected signature algorithm rsa_pss_rsae_sha512" \
-s "select_sig_alg_for_certificate_verify:no suitable signature algorithm found"
-S "ssl_tls13_pick_key_cert:check signature algorithm"
requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3
requires_config_enabled MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE
@ -12704,8 +12702,7 @@ run_test "TLS 1.3: Check server no suitable signature algorithm, m->m" \
"$P_CLI allow_sha1=0 debug_level=4 crt_file=data_files/server2-sha256.crt key_file=data_files/server2.key \
sig_algs=rsa_pkcs1_sha512,rsa_pss_rsae_sha512,ecdsa_secp521r1_sha512" \
1 \
-s "ssl_tls13_pick_key_cert:selected signature algorithm rsa_pss_rsae_sha512" \
-s "select_sig_alg_for_certificate_verify:no suitable signature algorithm found"
-S "ssl_tls13_pick_key_cert:check signature algorithm"
requires_gnutls_tls1_3
requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3