Implement ClientKeyExchange writing in PSA-based ECDHE suites
- Populate the ECDH private key slot with a fresh private EC key
designated for the correct algorithm.
- Export the public part of the ECDH private key from PSA and
reformat it to suite the format of the ClientKeyExchange message.
- Perform the PSA-based ECDH key agreement and store the result
as the premaster secret for the connection.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 7665f33..62c3695 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -3063,6 +3063,116 @@
}
else
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED */
+#if defined(MBEDTLS_USE_PSA_CRYPTO) && \
+ ( defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) || \
+ defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) )
+ if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
+ ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA )
+ {
+ psa_status_t status;
+ psa_key_policy_t policy;
+
+ mbedtls_ssl_handshake_params *handshake = ssl->handshake;
+
+ unsigned char own_pubkey[MBEDTLS_PSA_MAX_EC_PUBKEY_LENGTH];
+ size_t own_pubkey_len;
+ unsigned char *own_pubkey_ecpoint;
+ size_t own_pubkey_ecpoint_len;
+
+ psa_crypto_generator_t generator = PSA_CRYPTO_GENERATOR_INIT;
+
+ i = 4;
+
+ /*
+ * Generate EC private key for ECDHE exchange.
+ */
+
+ /* Allocate a new key slot for the private key. */
+
+ status = psa_allocate_key( &handshake->ecdh_psa_privkey );
+ if( status != PSA_SUCCESS )
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+
+ /* The master secret is obtained from the shared ECDH secret by
+ * applying the TLS 1.2 PRF with a specific salt and label. While
+ * the PSA Crypto API encourages combining key agreement schemes
+ * such as ECDH with fixed KDFs such as TLS 1.2 PRF, it does not
+ * yet support the provisioning of salt + label to the KDF.
+ * For the time being, we therefore need to split the computation
+ * of the ECDH secret and the application of the TLS 1.2 PRF. */
+ policy = psa_key_policy_init();
+ psa_key_policy_set_usage( &policy,
+ PSA_KEY_USAGE_DERIVE,
+ PSA_ALG_ECDH( PSA_ALG_SELECT_RAW ) );
+ status = psa_set_key_policy( handshake->ecdh_psa_privkey, &policy );
+ if( status != PSA_SUCCESS )
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+
+ /* Generate ECDH private key. */
+ status = psa_generate_key( handshake->ecdh_psa_privkey,
+ PSA_KEY_TYPE_ECC_KEYPAIR( handshake->ecdh_psa_curve ),
+ MBEDTLS_PSA_ECC_KEY_BITS_OF_CURVE( handshake->ecdh_psa_curve ),
+ NULL, 0 );
+ if( status != PSA_SUCCESS )
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+
+ /* Export the public part of the ECDH private key from PSA
+ * and convert it to ECPoint format used in ClientKeyExchange. */
+ status = psa_export_public_key( handshake->ecdh_psa_privkey,
+ own_pubkey, sizeof( own_pubkey ),
+ &own_pubkey_len );
+ if( status != PSA_SUCCESS )
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+
+ if( mbedtls_psa_tls_psa_ec_to_ecpoint( own_pubkey,
+ own_pubkey_len,
+ &own_pubkey_ecpoint,
+ &own_pubkey_ecpoint_len ) != 0 )
+ {
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+ }
+
+ /* Copy ECPoint structure to outgoing message buffer. */
+ ssl->out_msg[i] = own_pubkey_ecpoint_len;
+ memcpy( ssl->out_msg + i + 1, own_pubkey_ecpoint, own_pubkey_ecpoint_len );
+ n = own_pubkey_ecpoint_len + 1;
+
+ /* Compute ECDH shared secret. */
+ status = psa_key_agreement( &generator,
+ handshake->ecdh_psa_privkey,
+ handshake->ecdh_psa_peerkey,
+ handshake->ecdh_psa_peerkey_len,
+ PSA_ALG_ECDH( PSA_ALG_SELECT_RAW ) );
+ if( status != PSA_SUCCESS )
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+
+ /* The ECDH secret is the premaster secret used for key derivation. */
+
+ ssl->handshake->pmslen =
+ MBEDTLS_PSA_ECC_KEY_BYTES_OF_CURVE( handshake->ecdh_psa_curve );
+
+ status = psa_generator_read( &generator,
+ ssl->handshake->premaster,
+ ssl->handshake->pmslen );
+ if( status != PSA_SUCCESS )
+ {
+ psa_generator_abort( &generator );
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+ }
+
+ status = psa_generator_abort( &generator );
+ if( status != PSA_SUCCESS )
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+
+ status = psa_destroy_key( handshake->ecdh_psa_privkey );
+ if( status != PSA_SUCCESS )
+ return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+ handshake->ecdh_psa_privkey = 0;
+ }
+ else
+#endif /* MBEDTLS_USE_PSA_CRYPTO &&
+ ( MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
+ MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ) */
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) || \
defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) || \
defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
