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Implement ClientKeyExchange writing in PSA-based ECDHE suites

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- 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.
This commit is contained in:
Hanno Becker 2019-01-08 11:39:35 +00:00
parent bb89e2727f
commit 4a63ed421c
2 changed files with 115 additions and 0 deletions
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110
library/ssl_cli.c
View File

@ -3063,6 +3063,116 @@ static int ssl_write_client_key_exchange( mbedtls_ssl_context *ssl )
}
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) || \

5
library/ssl_tls.c
View File

@ -9367,6 +9367,11 @@ void mbedtls_ssl_handshake_free( mbedtls_ssl_context *ssl )
ssl_buffering_free( ssl );
#endif
#if defined(MBEDTLS_ECDH_C) && \
defined(MBEDTLS_USE_PSA_CRYPTO)
psa_destroy_key( handshake->ecdh_psa_privkey );
#endif /* MBEDTLS_ECDH_C && MBEDTLS_USE_PSA_CRYPTO */
mbedtls_platform_zeroize( handshake,
sizeof( mbedtls_ssl_handshake_params ) );
}