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Implement TLS-Exporter feature

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The TLS-Exporter is a function to derive shared symmetric keys for the
server and client from the secrets generated during the handshake.
It is defined in RFC 8446, Section 7.5 for TLS 1.3 and in RFC 5705 for
TLS 1.2.

Signed-off-by: Max Fillinger <maximilian.fillinger@foxcrypto.com>
This commit is contained in:
Max Fillinger
2024-07-22 14:43:56 +02:00
parent 064f68ec85
commit bd81c9d0f7
4 changed files with 169 additions and 0 deletions
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34
library/ssl_tls13_keys.c
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@ -1824,4 +1824,38 @@ int mbedtls_ssl_tls13_export_handshake_psk(mbedtls_ssl_context *ssl,
}
#endif /* MBEDTLS_SSL_TLS1_3_KEY_EXCHANGE_MODE_SOME_PSK_ENABLED */
int mbedtls_ssl_tls13_exporter(const psa_algorithm_t hash_alg,
const unsigned char *secret, const size_t secret_len,
const unsigned char *label, const size_t label_len,
const unsigned char *context_value, const size_t context_len,
unsigned char *out, const size_t out_len)
{
size_t hash_len = PSA_HASH_LENGTH(hash_alg);
unsigned char hkdf_secret[MBEDTLS_TLS1_3_MD_MAX_SIZE];
unsigned char hashed_context[PSA_HASH_MAX_SIZE];
size_t hashed_context_len = 0;
int ret = 0;
psa_status_t status = 0;
ret = mbedtls_ssl_tls13_derive_secret(hash_alg, secret, secret_len, label, label_len, NULL, 0,
MBEDTLS_SSL_TLS1_3_CONTEXT_UNHASHED, hkdf_secret, hash_len);
if (ret != 0) {
goto exit;
}
status = psa_hash_compute(hash_alg, context_value, context_len, hashed_context, hash_len, &hashed_context_len);
if (status != PSA_SUCCESS) {
ret = PSA_TO_MBEDTLS_ERR(status);
goto exit;
}
ret = mbedtls_ssl_tls13_hkdf_expand_label(hash_alg, hkdf_secret, hash_len,
MBEDTLS_SSL_TLS1_3_LBL_WITH_LEN(exporter),
hashed_context, hashed_context_len,
out, out_len);
exit:
mbedtls_platform_zeroize(hkdf_secret, sizeof(hkdf_secret));
return ret;
}
#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */