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/*
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed
* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
#include "crypto/s2n_tls13_keys.h"
#include <stdio.h>
#include "crypto/s2n_hkdf.h"
#include "crypto/s2n_hmac.h"
#include "error/s2n_errno.h"
#include "stuffer/s2n_stuffer.h"
#include "utils/s2n_blob.h"
#include "utils/s2n_mem.h"
#include "utils/s2n_safety.h"
/*
* There are 9 keys that can be generated by the end of a TLS 1.3 handshake.
* We currently support the following, more will be supported
* when the relevant TLS 1.3 features are worked on.
*
* [x] binder_key
* [x] client_early_traffic_secret
* [ ] early_exporter_master_secret
* [x] client_handshake_traffic_secret
* [x] server_handshake_traffic_secret
* [x] client_application_traffic_secret_0
* [x] server_application_traffic_secret_0
* [x] exporter_master_secret
* [x] resumption_master_secret
*
* The TLS 1.3 key generation can be divided into 3 phases
* 1. early secrets
* 2. handshake secrets
* 3. master secrets
*
* In each phase, secrets are first extracted with HKDF-Extract that takes in
* both an ikm (input keying material) and a salt. Some keys can be derived/expanded
* from the extract before a "tls13 derived" Derive-Secret is used to
* derive the input salt for the next phase.
*/
/*
* Define TLS 1.3 HKDF labels as specified in
* https://tools.ietf.org/html/rfc8446#section-7.1
*/
S2N_BLOB_LABEL(s2n_tls13_label_derived_secret, "derived")
S2N_BLOB_LABEL(s2n_tls13_label_external_psk_binder_key, "ext binder")
S2N_BLOB_LABEL(s2n_tls13_label_resumption_psk_binder_key, "res binder")
S2N_BLOB_LABEL(s2n_tls13_label_client_early_traffic_secret, "c e traffic")
S2N_BLOB_LABEL(s2n_tls13_label_early_exporter_master_secret, "e exp master")
S2N_BLOB_LABEL(s2n_tls13_label_client_handshake_traffic_secret, "c hs traffic")
S2N_BLOB_LABEL(s2n_tls13_label_server_handshake_traffic_secret, "s hs traffic")
S2N_BLOB_LABEL(s2n_tls13_label_client_application_traffic_secret, "c ap traffic")
S2N_BLOB_LABEL(s2n_tls13_label_server_application_traffic_secret, "s ap traffic")
S2N_BLOB_LABEL(s2n_tls13_label_exporter_master_secret, "exp master")
S2N_BLOB_LABEL(s2n_tls13_label_resumption_master_secret, "res master")
S2N_BLOB_LABEL(s2n_tls13_label_session_ticket_secret, "resumption")
/*
* Traffic secret labels
*/
S2N_BLOB_LABEL(s2n_tls13_label_traffic_secret_key, "key")
S2N_BLOB_LABEL(s2n_tls13_label_traffic_secret_iv, "iv")
/*
* TLS 1.3 Exporter label
*/
S2N_BLOB_LABEL(s2n_tls13_label_exporter, "exporter")
/*
* TLS 1.3 Finished label
*/
S2N_BLOB_LABEL(s2n_tls13_label_finished, "finished")
/*
* TLS 1.3 KeyUpdate label
*/
S2N_BLOB_LABEL(s2n_tls13_label_application_traffic_secret_update, "traffic upd")
static const struct s2n_blob zero_length_blob = { .data = NULL, .size = 0 };
/*
* Initializes the tls13_keys struct
*/
int s2n_tls13_keys_init(struct s2n_tls13_keys *keys, s2n_hmac_algorithm alg)
{
POSIX_ENSURE_REF(keys);
keys->hmac_algorithm = alg;
POSIX_GUARD(s2n_hmac_hash_alg(alg, &keys->hash_algorithm));
POSIX_GUARD(s2n_hash_digest_size(keys->hash_algorithm, &keys->size));
POSIX_GUARD(s2n_blob_init(&keys->extract_secret, keys->extract_secret_bytes, keys->size));
POSIX_GUARD(s2n_blob_init(&keys->derive_secret, keys->derive_secret_bytes, keys->size));
POSIX_GUARD(s2n_hmac_new(&keys->hmac));
return 0;
}
/*
* Frees any allocation
*/
int s2n_tls13_keys_free(struct s2n_tls13_keys *keys)
{
POSIX_ENSURE_REF(keys);
POSIX_GUARD(s2n_hmac_free(&keys->hmac));
return 0;
}
/*
* Derive Traffic Key and IV based on input secret
*/
int s2n_tls13_derive_traffic_keys(struct s2n_tls13_keys *keys, struct s2n_blob *secret, struct s2n_blob *key, struct s2n_blob *iv)
{
POSIX_ENSURE_REF(keys);
POSIX_ENSURE_REF(secret);
POSIX_ENSURE_REF(key);
POSIX_ENSURE_REF(iv);
POSIX_GUARD(s2n_hkdf_expand_label(&keys->hmac, keys->hmac_algorithm, secret,
&s2n_tls13_label_traffic_secret_key, &zero_length_blob, key));
POSIX_GUARD(s2n_hkdf_expand_label(&keys->hmac, keys->hmac_algorithm, secret,
&s2n_tls13_label_traffic_secret_iv, &zero_length_blob, iv));
return 0;
}
/*
* Generate finished key for compute finished hashes/MACs
* https://tools.ietf.org/html/rfc8446#section-4.4.4
*/
int s2n_tls13_derive_finished_key(struct s2n_tls13_keys *keys, struct s2n_blob *secret_key, struct s2n_blob *output_finish_key)
{
POSIX_GUARD(s2n_hkdf_expand_label(&keys->hmac, keys->hmac_algorithm, secret_key, &s2n_tls13_label_finished, &zero_length_blob, output_finish_key));
return 0;
}
/*
* Compute finished verify data using HMAC
* with a finished key and hash state
* https://tools.ietf.org/html/rfc8446#section-4.4.4
*/
int s2n_tls13_calculate_finished_mac(struct s2n_tls13_keys *keys, struct s2n_blob *finished_key, struct s2n_hash_state *hash_state, struct s2n_blob *finished_verify)
{
s2n_tls13_key_blob(transcript_hash, keys->size);
POSIX_GUARD(s2n_hash_digest(hash_state, transcript_hash.data, transcript_hash.size));
POSIX_GUARD(s2n_hkdf_extract(&keys->hmac, keys->hmac_algorithm, finished_key, &transcript_hash, finished_verify));
return S2N_SUCCESS;
}
/*
* Derives next generation of traffic secret
*/
int s2n_tls13_update_application_traffic_secret(struct s2n_tls13_keys *keys, struct s2n_blob *old_secret, struct s2n_blob *new_secret)
{
POSIX_ENSURE_REF(keys);
POSIX_ENSURE_REF(old_secret);
POSIX_ENSURE_REF(new_secret);
POSIX_GUARD(s2n_hkdf_expand_label(&keys->hmac, keys->hmac_algorithm, old_secret,
&s2n_tls13_label_application_traffic_secret_update, &zero_length_blob, new_secret));
return 0;
}
S2N_RESULT s2n_tls13_derive_session_ticket_secret(struct s2n_tls13_keys *keys, struct s2n_blob *resumption_secret,
struct s2n_blob *ticket_nonce, struct s2n_blob *secret_blob)
{
RESULT_ENSURE_REF(keys);
RESULT_ENSURE_REF(resumption_secret);
RESULT_ENSURE_REF(ticket_nonce);
RESULT_ENSURE_REF(secret_blob);
/* Derive session ticket secret from master session resumption secret */
RESULT_GUARD_POSIX(s2n_hkdf_expand_label(&keys->hmac, keys->hmac_algorithm, resumption_secret,
&s2n_tls13_label_session_ticket_secret, ticket_nonce, secret_blob));
return S2N_RESULT_OK;
}
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