path: root/contrib/restricted/aws/s2n/tls/s2n_tls13_handshake.c

/*
 * 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 "tls/s2n_tls13_handshake.h"
#include "tls/s2n_cipher_suites.h"
#include "tls/s2n_security_policies.h"

static int s2n_zero_sequence_number(struct s2n_connection *conn, s2n_mode mode)
{
    notnull_check(conn);
    struct s2n_blob sequence_number;
    if (mode == S2N_CLIENT) {
        GUARD(s2n_blob_init(&sequence_number, conn->secure.client_sequence_number, sizeof(conn->secure.client_sequence_number)));
    } else {
        GUARD(s2n_blob_init(&sequence_number, conn->secure.server_sequence_number, sizeof(conn->secure.server_sequence_number)));
    }
    GUARD(s2n_blob_zero(&sequence_number));
    return S2N_SUCCESS;
}

int s2n_tls13_mac_verify(struct s2n_tls13_keys *keys, struct s2n_blob *finished_verify, struct s2n_blob *wire_verify)
{
    notnull_check(wire_verify->data);
    eq_check(wire_verify->size, keys->size);

    S2N_ERROR_IF(!s2n_constant_time_equals(finished_verify->data, wire_verify->data, keys->size), S2N_ERR_BAD_MESSAGE);

    return 0;
}

/*
 * Initializes the tls13_keys struct
 */
static int s2n_tls13_keys_init_with_ref(struct s2n_tls13_keys *handshake, s2n_hmac_algorithm alg, uint8_t * extract,  uint8_t * derive)
{
    notnull_check(handshake);

    handshake->hmac_algorithm = alg;
    GUARD(s2n_hmac_hash_alg(alg, &handshake->hash_algorithm));
    GUARD(s2n_hash_digest_size(handshake->hash_algorithm, &handshake->size));
    GUARD(s2n_blob_init(&handshake->extract_secret, extract, handshake->size));
    GUARD(s2n_blob_init(&handshake->derive_secret, derive, handshake->size));
    GUARD(s2n_hmac_new(&handshake->hmac));

    return 0;
}

int s2n_tls13_keys_from_conn(struct s2n_tls13_keys *keys, struct s2n_connection *conn)
{
    GUARD(s2n_tls13_keys_init_with_ref(keys, conn->secure.cipher_suite->prf_alg, conn->secure.rsa_premaster_secret, conn->secure.master_secret));

    return 0;
}

int s2n_tls13_compute_ecc_shared_secret(struct s2n_connection *conn, struct s2n_blob *shared_secret) {
    notnull_check(conn);

    const struct s2n_ecc_preferences *ecc_preferences = NULL;
    GUARD(s2n_connection_get_ecc_preferences(conn, &ecc_preferences));
    notnull_check(ecc_preferences);

    struct s2n_ecc_evp_params *server_key = &conn->secure.server_ecc_evp_params;
    notnull_check(server_key);
    notnull_check(server_key->negotiated_curve);
    /* for now we do this tedious loop to find the matching client key selection.
     * this can be simplified if we get an index or a pointer to a specific key */
    int selection = -1;
    for (int i = 0; i < ecc_preferences->count; i++) {
        if (server_key->negotiated_curve->iana_id == ecc_preferences->ecc_curves[i]->iana_id) {
            selection = i;
            break;
        }
    }

    S2N_ERROR_IF(selection < 0, S2N_ERR_BAD_KEY_SHARE);
    struct s2n_ecc_evp_params *client_key = &conn->secure.client_ecc_evp_params[selection];
    notnull_check(client_key);

    if (conn->mode == S2N_CLIENT) {
        GUARD(s2n_ecc_evp_compute_shared_secret_from_params(client_key, server_key, shared_secret));
    } else {
        GUARD(s2n_ecc_evp_compute_shared_secret_from_params(server_key, client_key, shared_secret));
    }

    return 0;
}

/* Computes the ECDHE+PQKEM hybrid shared secret as defined in
 * https://tools.ietf.org/html/draft-stebila-tls-hybrid-design */
int s2n_tls13_compute_pq_hybrid_shared_secret(struct s2n_connection *conn, struct s2n_blob *shared_secret) {
    notnull_check(conn);
    notnull_check(shared_secret);

    /* conn->secure.server_ecc_evp_params should be set only during a classic/non-hybrid handshake */
    eq_check(NULL, conn->secure.server_ecc_evp_params.negotiated_curve);
    eq_check(NULL, conn->secure.server_ecc_evp_params.evp_pkey);

    struct s2n_kem_group_params *server_kem_group_params = &conn->secure.server_kem_group_params;
    notnull_check(server_kem_group_params);
    struct s2n_ecc_evp_params *server_ecc_params = &server_kem_group_params->ecc_params;
    notnull_check(server_ecc_params);

    struct s2n_kem_group_params *client_kem_group_params = conn->secure.chosen_client_kem_group_params;
    notnull_check(client_kem_group_params);
    struct s2n_ecc_evp_params *client_ecc_params = &client_kem_group_params->ecc_params;
    notnull_check(client_ecc_params);

    DEFER_CLEANUP(struct s2n_blob ecdhe_shared_secret = { 0 }, s2n_blob_zeroize_free);

    /* Compute the ECDHE shared secret, and retrieve the PQ shared secret. */
    if (conn->mode == S2N_CLIENT) {
        GUARD(s2n_ecc_evp_compute_shared_secret_from_params(client_ecc_params, server_ecc_params, &ecdhe_shared_secret));
    } else {
        GUARD(s2n_ecc_evp_compute_shared_secret_from_params(server_ecc_params, client_ecc_params, &ecdhe_shared_secret));
    }

    struct s2n_blob *pq_shared_secret = &client_kem_group_params->kem_params.shared_secret;
    notnull_check(pq_shared_secret);
    notnull_check(pq_shared_secret->data);

    const struct s2n_kem_group *negotiated_kem_group = conn->secure.server_kem_group_params.kem_group;
    notnull_check(negotiated_kem_group);
    notnull_check(negotiated_kem_group->kem);

    eq_check(pq_shared_secret->size, negotiated_kem_group->kem->shared_secret_key_length);

    /* Construct the concatenated/hybrid shared secret */
    uint32_t hybrid_shared_secret_size = ecdhe_shared_secret.size + negotiated_kem_group->kem->shared_secret_key_length;
    GUARD(s2n_alloc(shared_secret, hybrid_shared_secret_size));
    struct s2n_stuffer stuffer_combiner = { 0 };
    GUARD(s2n_stuffer_init(&stuffer_combiner, shared_secret));
    GUARD(s2n_stuffer_write(&stuffer_combiner, &ecdhe_shared_secret));
    GUARD(s2n_stuffer_write(&stuffer_combiner, pq_shared_secret));

    /* No longer need PQ shared secret or ECC keys */
    GUARD(s2n_kem_group_free(server_kem_group_params));
    GUARD(s2n_kem_group_free(client_kem_group_params));

    return S2N_SUCCESS;
}

static int s2n_tls13_pq_hybrid_supported(struct s2n_connection *conn) {
    return conn->secure.server_kem_group_params.kem_group != NULL;
}

int s2n_tls13_compute_shared_secret(struct s2n_connection *conn, struct s2n_blob *shared_secret)
{
    notnull_check(conn);

    if (s2n_tls13_pq_hybrid_supported(conn)) {
        GUARD(s2n_tls13_compute_pq_hybrid_shared_secret(conn, shared_secret));
    } else {
        GUARD(s2n_tls13_compute_ecc_shared_secret(conn, shared_secret));
    }

    return S2N_SUCCESS;
}

/*
 * This function executes after Server Hello is processed
 * and handshake hashes are computed. It produces and configure
 * the shared secret, handshake secrets, handshake traffic keys,
 * and finished keys.
 */
int s2n_tls13_handle_handshake_secrets(struct s2n_connection *conn)
{
    notnull_check(conn);
    const struct s2n_ecc_preferences *ecc_preferences = NULL;
    GUARD(s2n_connection_get_ecc_preferences(conn, &ecc_preferences));
    notnull_check(ecc_preferences);
    
    /* get tls13 key context */
    s2n_tls13_connection_keys(secrets, conn);

    /* get shared secret */
    DEFER_CLEANUP(struct s2n_blob shared_secret = { 0 }, s2n_free);
    GUARD(s2n_tls13_compute_shared_secret(conn, &shared_secret));

    /* derive early secrets */
    GUARD(s2n_tls13_derive_early_secrets(&secrets));

    /* produce handshake secrets */
    s2n_stack_blob(client_hs_secret, secrets.size, S2N_TLS13_SECRET_MAX_LEN);
    s2n_stack_blob(server_hs_secret, secrets.size, S2N_TLS13_SECRET_MAX_LEN);

    struct s2n_hash_state hash_state = {0};
    GUARD(s2n_handshake_get_hash_state(conn, secrets.hash_algorithm, &hash_state));
    GUARD(s2n_tls13_derive_handshake_secrets(&secrets, &shared_secret, &hash_state, &client_hs_secret, &server_hs_secret));

    /* trigger secret callbacks */
    if (conn->secret_cb && conn->config->quic_enabled) {
        GUARD(conn->secret_cb(conn->secret_cb_context, conn, S2N_CLIENT_HANDSHAKE_TRAFFIC_SECRET,
                client_hs_secret.data, client_hs_secret.size));
        GUARD(conn->secret_cb(conn->secret_cb_context, conn, S2N_SERVER_HANDSHAKE_TRAFFIC_SECRET,
                server_hs_secret.data, server_hs_secret.size));
    }

    /* produce handshake traffic keys and configure record algorithm */
    s2n_tls13_key_blob(server_hs_key, conn->secure.cipher_suite->record_alg->cipher->key_material_size);
    struct s2n_blob server_hs_iv = { .data = conn->secure.server_implicit_iv, .size = S2N_TLS13_FIXED_IV_LEN };
    GUARD(s2n_tls13_derive_traffic_keys(&secrets, &server_hs_secret, &server_hs_key, &server_hs_iv));

    s2n_tls13_key_blob(client_hs_key, conn->secure.cipher_suite->record_alg->cipher->key_material_size);
    struct s2n_blob client_hs_iv = { .data = conn->secure.client_implicit_iv, .size = S2N_TLS13_FIXED_IV_LEN };
    GUARD(s2n_tls13_derive_traffic_keys(&secrets, &client_hs_secret, &client_hs_key, &client_hs_iv));

    GUARD(conn->secure.cipher_suite->record_alg->cipher->init(&conn->secure.server_key));
    GUARD(conn->secure.cipher_suite->record_alg->cipher->init(&conn->secure.client_key));

    if (conn->mode == S2N_CLIENT) {
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_decryption_key(&conn->secure.server_key, &server_hs_key));
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_encryption_key(&conn->secure.client_key, &client_hs_key));
    } else {
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_encryption_key(&conn->secure.server_key, &server_hs_key));
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_decryption_key(&conn->secure.client_key, &client_hs_key));
    }

    /* calculate server + client finished keys and store them in handshake struct */
    struct s2n_blob server_finished_key = { .data = conn->handshake.server_finished, .size = secrets.size };
    struct s2n_blob client_finished_key = { .data = conn->handshake.client_finished, .size = secrets.size };
    GUARD(s2n_tls13_derive_finished_key(&secrets, &server_hs_secret, &server_finished_key));
    GUARD(s2n_tls13_derive_finished_key(&secrets, &client_hs_secret, &client_finished_key));

    /* since shared secret has been computed, clean up keys */
    GUARD(s2n_ecc_evp_params_free(&conn->secure.server_ecc_evp_params));
    for (int i = 0; i < ecc_preferences->count; i++) {
        GUARD(s2n_ecc_evp_params_free(&conn->secure.client_ecc_evp_params[i]));
    }

    /* According to https://tools.ietf.org/html/rfc8446#section-5.3:
     * Each sequence number is set to zero at the beginning of a connection and
     * whenever the key is changed
     */
    GUARD(s2n_zero_sequence_number(conn, S2N_CLIENT));
    GUARD(s2n_zero_sequence_number(conn, S2N_SERVER));

    return 0;
}

static int s2n_tls13_handle_application_secret(struct s2n_connection *conn, s2n_mode mode)
{
    /* get tls13 key context */
    s2n_tls13_connection_keys(keys, conn);
    bool is_sending_secret = (mode == conn->mode);

    uint8_t *app_secret_data, *implicit_iv_data;
    struct s2n_session_key *session_key;
    s2n_secret_type_t secret_type;
    if (mode == S2N_CLIENT) {
        app_secret_data = conn->secure.client_app_secret;
        implicit_iv_data = conn->secure.client_implicit_iv;
        session_key = &conn->secure.client_key;
        secret_type = S2N_CLIENT_APPLICATION_TRAFFIC_SECRET;
    } else {
        app_secret_data = conn->secure.server_app_secret;
        implicit_iv_data = conn->secure.server_implicit_iv;
        session_key = &conn->secure.server_key;
        secret_type = S2N_SERVER_APPLICATION_TRAFFIC_SECRET;
    }

    /* use frozen hashes during the server finished state */
    struct s2n_hash_state *hash_state;
    GUARD_NONNULL(hash_state = &conn->handshake.server_finished_copy);

    /* calculate secret */
    struct s2n_blob app_secret = { .data = app_secret_data, .size = keys.size };
    GUARD(s2n_tls13_derive_application_secret(&keys, hash_state, &app_secret, mode));

    /* trigger secret callback */
    if (conn->secret_cb && conn->config->quic_enabled) {
        GUARD(conn->secret_cb(conn->secret_cb_context, conn, secret_type,
                app_secret.data, app_secret.size));
    }

    /* derive key from secret */
    s2n_tls13_key_blob(app_key, conn->secure.cipher_suite->record_alg->cipher->key_material_size);
    struct s2n_blob app_iv = { .data = implicit_iv_data, .size = S2N_TLS13_FIXED_IV_LEN };
    GUARD(s2n_tls13_derive_traffic_keys(&keys, &app_secret, &app_key, &app_iv));

    /* update record algorithm secrets */
    if (is_sending_secret) {
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_encryption_key(session_key, &app_key));
    } else {
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_decryption_key(session_key, &app_key));
    }

    /* According to https://tools.ietf.org/html/rfc8446#section-5.3:
     * Each sequence number is set to zero at the beginning of a connection and
     * whenever the key is changed
     */
    GUARD(s2n_zero_sequence_number(conn, mode));

    return S2N_SUCCESS;
}

/* The application secrets are derived from the master secret, so the
 * master secret must be handled BEFORE the application secrets.
 */
static int s2n_tls13_handle_master_secret(struct s2n_connection *conn)
{
    s2n_tls13_connection_keys(keys, conn);
    GUARD(s2n_tls13_extract_master_secret(&keys));
    return S2N_SUCCESS;
}

int s2n_tls13_handle_secrets(struct s2n_connection *conn)
{
    notnull_check(conn);
    if (conn->actual_protocol_version < S2N_TLS13) {
        return S2N_SUCCESS;
    }

    switch(s2n_conn_get_current_message_type(conn)) {
        case SERVER_HELLO:
            GUARD(s2n_tls13_handle_handshake_secrets(conn));
            /* Set negotiated crypto parameters for encryption */
            conn->server = &conn->secure;
            conn->client = &conn->secure;
            break;
        case SERVER_FINISHED:
            if (conn->mode == S2N_SERVER) {
                GUARD(s2n_tls13_handle_master_secret(conn));
                GUARD(s2n_tls13_handle_application_secret(conn, S2N_SERVER));
            }
            break;
        case CLIENT_FINISHED:
            if (conn->mode == S2N_CLIENT) {
                GUARD(s2n_tls13_handle_master_secret(conn));
                GUARD(s2n_tls13_handle_application_secret(conn, S2N_SERVER));
            }
            GUARD(s2n_tls13_handle_application_secret(conn, S2N_CLIENT));
            break;
        default:
            break;
    }
    return S2N_SUCCESS;
}

int s2n_update_application_traffic_keys(struct s2n_connection *conn, s2n_mode mode, keyupdate_status status)
{
    notnull_check(conn);
    
    /* get tls13 key context */
    s2n_tls13_connection_keys(keys, conn);

    struct s2n_session_key *old_key;
    struct s2n_blob old_app_secret;
    struct s2n_blob app_iv;

    if (mode == S2N_CLIENT) {
        old_key = &conn->secure.client_key;
        GUARD(s2n_blob_init(&old_app_secret, conn->secure.client_app_secret, keys.size));
        GUARD(s2n_blob_init(&app_iv, conn->secure.client_implicit_iv, S2N_TLS13_FIXED_IV_LEN));
    } else {
        old_key = &conn->secure.server_key;
        GUARD(s2n_blob_init(&old_app_secret, conn->secure.server_app_secret, keys.size));
        GUARD(s2n_blob_init(&app_iv, conn->secure.server_implicit_iv, S2N_TLS13_FIXED_IV_LEN));  
    }

    /* Produce new application secret */
    s2n_stack_blob(app_secret_update, keys.size, S2N_TLS13_SECRET_MAX_LEN);

    /* Derives next generation of traffic secret */
    GUARD(s2n_tls13_update_application_traffic_secret(&keys, &old_app_secret, &app_secret_update));

    s2n_tls13_key_blob(app_key, conn->secure.cipher_suite->record_alg->cipher->key_material_size);

    /* Derives next generation of traffic key */
    GUARD(s2n_tls13_derive_traffic_keys(&keys, &app_secret_update, &app_key, &app_iv));
    if (status == RECEIVING) {
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_decryption_key(old_key, &app_key));
    } else {
        GUARD(conn->secure.cipher_suite->record_alg->cipher->set_encryption_key(old_key, &app_key));
    }

    /* According to https://tools.ietf.org/html/rfc8446#section-5.3:
     * Each sequence number is set to zero at the beginning of a connection and
     * whenever the key is changed; the first record transmitted under a particular traffic key
     * MUST use sequence number 0.
     */
    GUARD(s2n_zero_sequence_number(conn, mode));
    
    /* Save updated secret */
    struct s2n_stuffer old_secret_stuffer = {0};
    GUARD(s2n_stuffer_init(&old_secret_stuffer, &old_app_secret));
    GUARD(s2n_stuffer_write_bytes(&old_secret_stuffer, app_secret_update.data, keys.size));

    return S2N_SUCCESS;
}