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Upgrade the default TLS hash and curve selection, matching X.509

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Upgrade the default list of hashes and curves allowed for TLS. The list is
now aligned with X.509 certificate verification: hashes and curves with at
least 255 bits (Curve25519 included), and RSA 2048 and above.

Remove MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE which would no
longer do anything.

Document more precisely what is allowed by default.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-06-02 00:05:29 +02:00
parent ffb92da622
commit ae270bf386
5 changed files with 63 additions and 30 deletions
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52
library/ssl_tls.c
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@ -6098,6 +6098,11 @@ void mbedtls_ssl_config_init( mbedtls_ssl_config *conf )
}
#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/* The selection should be the same as mbedtls_x509_crt_profile_default in
* x509_crt.c. Here, the order matters: larger hashes first, for consistency
* with curves.
* See the documentation of mbedtls_ssl_conf_curves() for what we promise
* about this list. */
static int ssl_preset_default_hashes[] = {
#if defined(MBEDTLS_SHA512_C)
MBEDTLS_MD_SHA512,
@ -6107,17 +6112,50 @@ static int ssl_preset_default_hashes[] = {
#endif
#if defined(MBEDTLS_SHA256_C)
MBEDTLS_MD_SHA256,
#endif
#if defined(MBEDTLS_SHA224_C)
MBEDTLS_MD_SHA224,
#endif
#if defined(MBEDTLS_SHA1_C) && defined(MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE)
MBEDTLS_MD_SHA1,
#endif
MBEDTLS_MD_NONE
};
#endif
#if defined(MBEDTLS_ECP_C)
/* The selection should be the same as mbedtls_x509_crt_profile_default in
* x509_crt.c, plus Montgomery curves for ECDHE. Here, the order matters:
* larger curves first, like ecp_supported_curves in ecp.c.
* See the documentation of mbedtls_ssl_conf_curves() for what we promise
* about this list. */
static mbedtls_ecp_group_id ssl_preset_default_curves[] = {
#if defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
MBEDTLS_ECP_DP_SECP521R1,
#endif
#if defined(MBEDTLS_ECP_DP_BP512R1_ENABLED)
MBEDTLS_ECP_DP_BP512R1,
#endif
#if defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
MBEDTLS_ECP_DP_CURVE448,
#endif
#if defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
MBEDTLS_ECP_DP_SECP384R1,
#endif
#if defined(MBEDTLS_ECP_DP_BP384R1_ENABLED)
MBEDTLS_ECP_DP_BP384R1,
#endif
#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
// Positioned in the list as a fast 256-bit curve, not as a 255-bit curve
MBEDTLS_ECP_DP_CURVE25519,
#endif
#if defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
MBEDTLS_ECP_DP_SECP256R1,
#endif
#if defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED)
MBEDTLS_ECP_DP_SECP256K1,
#endif
#if defined(MBEDTLS_ECP_DP_BP256R1_ENABLED)
MBEDTLS_ECP_DP_BP256R1,
#endif
MBEDTLS_ECP_DP_NONE
};
#endif
static int ssl_preset_suiteb_ciphersuites[] = {
MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
@ -6281,7 +6319,7 @@ int mbedtls_ssl_config_defaults( mbedtls_ssl_config *conf,
#endif
#if defined(MBEDTLS_ECP_C)
conf->curve_list = mbedtls_ecp_grp_id_list();
conf->curve_list = ssl_preset_default_curves;
#endif
#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_CLI_C)