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2aee73ed90
mlkem768x25519-sha256) from markus@ OpenBSD-Commit-ID: 9c72e9c0407906bb7d5fb16648b38282676391e9
309 lines
8.9 KiB
C
309 lines
8.9 KiB
C
/* $OpenBSD: kexmlkem768ecdh.c,v 1.4 2026/08/03 06:43:16 djm Exp $ */
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/*
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* Copyright (c) 2025 Markus Friedl. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "includes.h"
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#include <sys/types.h>
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#include <stdio.h>
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#include <stdint.h>
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#include <stdbool.h>
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#include <string.h>
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#include <signal.h>
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#include <endian.h>
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#include "sshkey.h"
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#include "kex.h"
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#include "sshbuf.h"
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#include "digest.h"
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#include "ssherr.h"
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#ifdef WITH_OPENSSL
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int
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kex_kem_mlkem768ecdh_keypair(struct kex *kex)
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{
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struct sshbuf *buf = NULL;
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struct sshbuf *ec_blob = NULL;
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EC_KEY *client_key = NULL;
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const EC_GROUP *group;
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const EC_POINT *public_key;
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u_char *cp = NULL;
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size_t need;
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int r = SSH_ERR_INTERNAL_ERROR;
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if ((buf = sshbuf_new()) == NULL)
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return SSH_ERR_ALLOC_FAIL;
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need = MLKEM768_PUBLICKEYBYTES;
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if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
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goto out;
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if (crypto_kem_mlkem768_keypair(cp, kex->mlkem768_client_key) != 0) {
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r = SSH_ERR_INTERNAL_ERROR;
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goto out;
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}
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#ifdef DEBUG_KEXECDH
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dump_digest("client public key mlkem768:", cp,
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MLKEM768_PUBLICKEYBYTES);
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#endif
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if ((client_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if (EC_KEY_generate_key(client_key) != 1) {
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r = SSH_ERR_LIBCRYPTO_ERROR;
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goto out;
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}
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group = EC_KEY_get0_group(client_key);
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public_key = EC_KEY_get0_public_key(client_key);
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if ((ec_blob = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if ((r = sshbuf_put_ec(ec_blob, public_key, group)) != 0 ||
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(r = sshbuf_get_u32(ec_blob, NULL)) != 0 ||
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(r = sshbuf_putb(buf, ec_blob)) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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fputs("client private key EC:\n", stderr);
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sshkey_dump_ec_key(client_key);
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#endif
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/* success */
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r = 0;
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kex->ec_client_key = client_key;
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kex->ec_group = group;
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client_key = NULL; /* owned by the kex */
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kex->client_pub = buf;
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buf = NULL;
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out:
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sshbuf_free(buf);
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sshbuf_free(ec_blob);
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EC_KEY_free(client_key);
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return r;
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}
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int
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kex_kem_mlkem768ecdh_enc(struct kex *kex,
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const struct sshbuf *client_blob, struct sshbuf **server_blobp,
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struct sshbuf **shared_secretp)
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{
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const EC_GROUP *group;
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const EC_POINT *pub_key;
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EC_KEY *server_key = NULL;
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struct sshbuf *ec_pub = NULL;
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struct sshbuf *ec_blob = NULL;
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struct sshbuf *ec_shared = NULL;
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struct sshbuf *server_blob = NULL;
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struct sshbuf *buf = NULL;
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const u_char *client_pub;
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u_char hash[SSH_DIGEST_MAX_LENGTH];
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u_char ct[MLKEM768_CIPHERTEXTBYTES];
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u_char shared_secret[MLKEM768_BYTES];
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size_t need;
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int r = SSH_ERR_INTERNAL_ERROR;
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*server_blobp = NULL;
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*shared_secretp = NULL;
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/* client_blob contains both KEM and ECDH client pubkeys */
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need = MLKEM768_PUBLICKEYBYTES;
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if (sshbuf_len(client_blob) <= need) {
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r = SSH_ERR_SIGNATURE_INVALID;
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goto out;
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}
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client_pub = sshbuf_ptr(client_blob);
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#ifdef DEBUG_KEXECDH
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dump_digest("client public key mlkem768:", client_pub,
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MLKEM768_PUBLICKEYBYTES);
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#endif
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/* allocate buffer for concatenation of KEM key and ECDH shared key */
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/* the buffer will be hashed and the result is the shared secret */
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if ((buf = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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/* allocate space for encrypted KEM key and ECDH pub key */
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if ((server_blob = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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/* generate and encrypt KEM key with client key */
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if (crypto_kem_mlkem768_enc(ct, shared_secret, client_pub) != 0) {
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r = SSH_ERR_INTERNAL_ERROR;
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goto out;
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}
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if ((r = sshbuf_put(buf, shared_secret, sizeof(shared_secret))) != 0 ||
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(r = sshbuf_put(server_blob, ct, sizeof(ct))) != 0)
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goto out;
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client_pub += MLKEM768_PUBLICKEYBYTES;
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if ((ec_pub = sshbuf_from(client_pub, sshbuf_len(client_blob) -
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MLKEM768_PUBLICKEYBYTES)) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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/* generate ECDH key pair */
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if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if (EC_KEY_generate_key(server_key) != 1) {
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r = SSH_ERR_LIBCRYPTO_ERROR;
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goto out;
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}
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group = EC_KEY_get0_group(server_key);
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#ifdef DEBUG_KEXECDH
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fputs("server private key EC:\n", stderr);
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sshkey_dump_ec_key(server_key);
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#endif
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/* store server pubkey after ciphertext */
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pub_key = EC_KEY_get0_public_key(server_key);
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if ((ec_blob = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if ((r = sshbuf_put_ec(ec_blob, pub_key, group)) != 0 ||
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(r = sshbuf_get_u32(ec_blob, NULL)) != 0 ||
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(r = sshbuf_putb(server_blob, ec_blob)) != 0)
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goto out;
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/* append ECDH shared key */
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if ((r = kex_ecdh_dec_key_group(kex, ec_pub, server_key, group,
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1, &ec_shared)) != 0 ||
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(r = sshbuf_putb(buf, ec_shared)) != 0)
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goto out;
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if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("server cipher text:", ct, sizeof(ct));
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dump_digest("server kem key:", shared_secret, sizeof(shared_secret));
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dump_digest("concatenation of KEM key and ECDH shared key:",
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sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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/* string-encoded hash is resulting shared secret */
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sshbuf_reset(buf);
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if ((r = sshbuf_put_string(buf, hash,
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ssh_digest_bytes(kex->hash_alg))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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/* success */
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r = 0;
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*server_blobp = server_blob;
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*shared_secretp = buf;
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server_blob = NULL;
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buf = NULL;
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out:
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explicit_bzero(hash, sizeof(hash));
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explicit_bzero(shared_secret, sizeof(shared_secret));
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EC_KEY_free(server_key);
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sshbuf_free(ec_pub);
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sshbuf_free(ec_blob);
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sshbuf_free(ec_shared);
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sshbuf_free(server_blob);
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sshbuf_free(buf);
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return r;
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}
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int
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kex_kem_mlkem768ecdh_dec(struct kex *kex,
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const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
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{
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struct sshbuf *buf = NULL;
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struct sshbuf *ec_pub = NULL;
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struct sshbuf *ec_shared = NULL;
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u_char shared_secret[MLKEM768_BYTES];
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const u_char *ciphertext, *server_pub;
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u_char hash[SSH_DIGEST_MAX_LENGTH];
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size_t need;
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int r;
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*shared_secretp = NULL;
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need = MLKEM768_CIPHERTEXTBYTES;
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if (sshbuf_len(server_blob) <= need) {
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r = SSH_ERR_SIGNATURE_INVALID;
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goto out;
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}
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ciphertext = sshbuf_ptr(server_blob);
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server_pub = ciphertext + MLKEM768_CIPHERTEXTBYTES;
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#ifdef DEBUG_KEXECDH
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dump_digest("server cipher text (dec):", ciphertext,
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MLKEM768_CIPHERTEXTBYTES);
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#endif
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/* hash concatenation of KEM key and ECDH shared key */
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if ((buf = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if (crypto_kem_mlkem768_dec(shared_secret, ciphertext,
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kex->mlkem768_client_key) != 0) {
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r = SSH_ERR_INTERNAL_ERROR;
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goto out;
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}
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if ((r = sshbuf_put(buf, shared_secret, sizeof(shared_secret))) != 0)
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goto out;
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if ((ec_pub = sshbuf_from(server_pub, sshbuf_len(server_blob) - need))
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== NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if ((r = kex_ecdh_dec_key_group(kex, ec_pub, kex->ec_client_key,
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kex->ec_group, 1, &ec_shared)) != 0 ||
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(r = sshbuf_putb(buf, ec_shared)) != 0)
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goto out;
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if ((r = ssh_digest_buffer(kex->hash_alg, buf,
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hash, sizeof(hash))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("client kem key:", shared_secret, sizeof(shared_secret));
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dump_digest("concatenation of KEM key and ECDH shared key:",
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sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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sshbuf_reset(buf);
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if ((r = sshbuf_put_string(buf, hash,
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ssh_digest_bytes(kex->hash_alg))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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/* success */
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r = 0;
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*shared_secretp = buf;
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buf = NULL;
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out:
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explicit_bzero(hash, sizeof(hash));
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explicit_bzero(shared_secret, sizeof(shared_secret));
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EC_KEY_free(kex->ec_client_key);
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kex->ec_client_key = NULL;
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sshbuf_free(ec_pub);
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sshbuf_free(ec_shared);
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sshbuf_free(buf);
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return r;
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}
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#endif /* WITH_OPENSSL */
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