Upgrade the default TLS hash and curve selection, matching X.509
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
parent
ffb92da622
commit
ae270bf386
5 changed files with 63 additions and 30 deletions
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@ -3326,23 +3326,6 @@
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//#define MBEDTLS_X509_MAX_INTERMEDIATE_CA 8 /**< Maximum number of intermediate CAs in a verification chain. */
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//#define MBEDTLS_X509_MAX_FILE_PATH_LEN 512 /**< Maximum length of a path/filename string in bytes including the null terminator character ('\0'). */
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/**
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* Allow SHA-1 in the default TLS configuration for TLS 1.2 handshake
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* signature and ciphersuite selection. Without this build-time option, SHA-1
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* support must be activated explicitly through mbedtls_ssl_conf_sig_hashes.
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* The use of SHA-1 in TLS <= 1.1 and in HMAC-SHA-1 is always allowed by
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* default. At the time of writing, there is no practical attack on the use
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* of SHA-1 in handshake signatures, hence this option is turned on by default
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* to preserve compatibility with existing peers, but the general
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* warning applies nonetheless:
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*
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* \warning SHA-1 is considered a weak message digest and its use constitutes
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* a security risk. If possible, we recommend avoiding dependencies
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* on it, and considering stronger message digests instead.
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*
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*/
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#define MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE
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/**
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* Uncomment the macro to let mbed TLS use your alternate implementation of
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* mbedtls_platform_zeroize(). This replaces the default implementation in
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@ -2893,7 +2893,6 @@ void mbedtls_ssl_conf_dhm_min_bitlen( mbedtls_ssl_config *conf,
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#if defined(MBEDTLS_ECP_C)
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/**
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* \brief Set the allowed curves in order of preference.
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* (Default: all defined curves.)
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*
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* On server: this only affects selection of the ECDHE curve;
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* the curves used for ECDH and ECDSA are determined by the
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@ -2914,6 +2913,12 @@ void mbedtls_ssl_conf_dhm_min_bitlen( mbedtls_ssl_config *conf,
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* \note This list should be ordered by decreasing preference
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* (preferred curve first).
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*
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* \note The default list is the same set of curves that
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* #mbedtls_x509_crt_profile_default allows, plus
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* ECDHE-only curves selected according to the same criteria.
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* Larger (generally more secure but slower) curves are
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* preferred over smaller curves.
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*
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* \param conf SSL configuration
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* \param curves Ordered list of allowed curves,
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* terminated by MBEDTLS_ECP_DP_NONE.
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@ -2925,7 +2930,6 @@ void mbedtls_ssl_conf_curves( mbedtls_ssl_config *conf,
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#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
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/**
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* \brief Set the allowed hashes for signatures during the handshake.
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* (Default: all available hashes except MD5.)
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*
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* \note This only affects which hashes are offered and can be used
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* for signatures during the handshake. Hashes for message
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@ -2937,6 +2941,12 @@ void mbedtls_ssl_conf_curves( mbedtls_ssl_config *conf,
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* \note This list should be ordered by decreasing preference
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* (preferred hash first).
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*
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* \note By default, all supported hashes whose length is at least
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* 256 bits are allowed. This is the same set as the default
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* for certificate verification
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* (#mbedtls_x509_crt_profile_default). Larger hashes are
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* preferred.
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*
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* \param conf SSL configuration
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* \param hashes Ordered list of allowed signature hashes,
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* terminated by \c MBEDTLS_MD_NONE.
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@ -509,9 +509,9 @@ int mbedtls_ecp_check_budget( const mbedtls_ecp_group *grp,
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* - readable name
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*
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* Curves are listed in order: largest curves first, and for a given size,
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* fastest curves first. This provides the default order for the SSL module.
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* fastest curves first.
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*
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* Reminder: update profiles in x509_crt.c when adding a new curves!
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* Reminder: update profiles in x509_crt.c and ssl_tls.c when adding a new curve!
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*/
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static const mbedtls_ecp_curve_info ecp_supported_curves[] =
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{
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@ -6098,6 +6098,11 @@ void mbedtls_ssl_config_init( mbedtls_ssl_config *conf )
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}
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#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
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/* The selection should be the same as mbedtls_x509_crt_profile_default in
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* x509_crt.c. Here, the order matters: larger hashes first, for consistency
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* with curves.
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* See the documentation of mbedtls_ssl_conf_curves() for what we promise
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* about this list. */
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static int ssl_preset_default_hashes[] = {
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#if defined(MBEDTLS_SHA512_C)
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MBEDTLS_MD_SHA512,
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@ -6107,17 +6112,50 @@ static int ssl_preset_default_hashes[] = {
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#endif
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#if defined(MBEDTLS_SHA256_C)
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MBEDTLS_MD_SHA256,
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#endif
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#if defined(MBEDTLS_SHA224_C)
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MBEDTLS_MD_SHA224,
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#endif
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#if defined(MBEDTLS_SHA1_C) && defined(MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE)
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MBEDTLS_MD_SHA1,
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#endif
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MBEDTLS_MD_NONE
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};
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#endif
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#if defined(MBEDTLS_ECP_C)
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/* The selection should be the same as mbedtls_x509_crt_profile_default in
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* x509_crt.c, plus Montgomery curves for ECDHE. Here, the order matters:
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* larger curves first, like ecp_supported_curves in ecp.c.
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* See the documentation of mbedtls_ssl_conf_curves() for what we promise
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* about this list. */
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static mbedtls_ecp_group_id ssl_preset_default_curves[] = {
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#if defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
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MBEDTLS_ECP_DP_SECP521R1,
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#endif
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#if defined(MBEDTLS_ECP_DP_BP512R1_ENABLED)
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MBEDTLS_ECP_DP_BP512R1,
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#endif
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#if defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
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MBEDTLS_ECP_DP_CURVE448,
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#endif
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#if defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
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MBEDTLS_ECP_DP_SECP384R1,
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#endif
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#if defined(MBEDTLS_ECP_DP_BP384R1_ENABLED)
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MBEDTLS_ECP_DP_BP384R1,
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#endif
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#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
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// Positioned in the list as a fast 256-bit curve, not as a 255-bit curve
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MBEDTLS_ECP_DP_CURVE25519,
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#endif
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#if defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
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MBEDTLS_ECP_DP_SECP256R1,
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#endif
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#if defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED)
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MBEDTLS_ECP_DP_SECP256K1,
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#endif
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#if defined(MBEDTLS_ECP_DP_BP256R1_ENABLED)
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MBEDTLS_ECP_DP_BP256R1,
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#endif
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MBEDTLS_ECP_DP_NONE
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};
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#endif
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static int ssl_preset_suiteb_ciphersuites[] = {
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MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
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MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
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@ -6281,7 +6319,7 @@ int mbedtls_ssl_config_defaults( mbedtls_ssl_config *conf,
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#endif
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#if defined(MBEDTLS_ECP_C)
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conf->curve_list = mbedtls_ecp_grp_id_list();
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conf->curve_list = ssl_preset_default_curves;
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#endif
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#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_CLI_C)
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@ -99,13 +99,15 @@ typedef struct {
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* concerns. */
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const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_default =
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{
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/* Hashes from SHA-256 and above */
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/* Hashes from SHA-256 and above. Note that this selection
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* should be aligned with ssl_preset_default_hashes in ssl_tls.c. */
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MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA256 ) |
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MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA384 ) |
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MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA512 ),
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0xFFFFFFF, /* Any PK alg */
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#if defined(MBEDTLS_ECP_C)
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/* Curves at or above 128-bit security level */
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/* Curves at or above 128-bit security level. Note that this selection
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* should be aligned with ssl_preset_default_curves in ssl_tls.c. */
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MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_SECP256R1 ) |
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MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_SECP384R1 ) |
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MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_SECP521R1 ) |
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