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/* $OpenBSD: kexmlkem768x25519.c,v 1.2 2024/10/27 02:06:59 djm Exp $ */
/*
* Copyright (c) 2023 Markus Friedl. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/types.h>
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <signal.h>
#include <endian.h>
#include "sshkey.h"
#include "kex.h"
#include "sshbuf.h"
#include "digest.h"
#include "ssherr.h"
#include "log.h"
#include "libcrux_mlkem768_sha3.h"
int
kex_kem_mlkem768x25519_keypair(struct kex *kex)
{
struct sshbuf *buf = NULL;
u_char rnd[LIBCRUX_ML_KEM_KEY_PAIR_PRNG_LEN], *cp = NULL;
size_t need;
int r = SSH_ERR_INTERNAL_ERROR;
struct libcrux_mlkem768_keypair keypair;
if ((buf = sshbuf_new()) == NULL)
return SSH_ERR_ALLOC_FAIL;
need = crypto_kem_mlkem768_PUBLICKEYBYTES + CURVE25519_SIZE;
if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
goto out;
arc4random_buf(rnd, sizeof(rnd));
keypair = libcrux_ml_kem_mlkem768_portable_generate_key_pair(rnd);
memcpy(cp, keypair.pk.value, crypto_kem_mlkem768_PUBLICKEYBYTES);
memcpy(kex->mlkem768_client_key, keypair.sk.value,
sizeof(kex->mlkem768_client_key));
#ifdef DEBUG_KEXECDH
dump_digest("client public key mlkem768:", cp,
crypto_kem_mlkem768_PUBLICKEYBYTES);
#endif
cp += crypto_kem_mlkem768_PUBLICKEYBYTES;
kexc25519_keygen(kex->c25519_client_key, cp);
#ifdef DEBUG_KEXECDH
dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
#endif
/* success */
r = 0;
kex->client_pub = buf;
buf = NULL;
out:
explicit_bzero(&keypair, sizeof(keypair));
explicit_bzero(rnd, sizeof(rnd));
sshbuf_free(buf);
return r;
}
int
kex_kem_mlkem768x25519_enc(struct kex *kex,
const struct sshbuf *client_blob, struct sshbuf **server_blobp,
struct sshbuf **shared_secretp)
{
struct sshbuf *server_blob = NULL;
struct sshbuf *buf = NULL;
const u_char *client_pub;
u_char rnd[LIBCRUX_ML_KEM_ENC_PRNG_LEN];
u_char server_pub[CURVE25519_SIZE], server_key[CURVE25519_SIZE];
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t need;
int r = SSH_ERR_INTERNAL_ERROR;
struct libcrux_mlkem768_enc_result enc;
struct libcrux_mlkem768_pk mlkem_pub;
*server_blobp = NULL;
*shared_secretp = NULL;
memset(&mlkem_pub, 0, sizeof(mlkem_pub));
/* client_blob contains both KEM and ECDH client pubkeys */
need = crypto_kem_mlkem768_PUBLICKEYBYTES + CURVE25519_SIZE;
if (sshbuf_len(client_blob) != need) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
client_pub = sshbuf_ptr(client_blob);
#ifdef DEBUG_KEXECDH
dump_digest("client public key mlkem768:", client_pub,
crypto_kem_mlkem768_PUBLICKEYBYTES);
dump_digest("client public key 25519:",
client_pub + crypto_kem_mlkem768_PUBLICKEYBYTES,
CURVE25519_SIZE);
#endif
/* check public key validity */
memcpy(mlkem_pub.value, client_pub, crypto_kem_mlkem768_PUBLICKEYBYTES);
if (!libcrux_ml_kem_mlkem768_portable_validate_public_key(&mlkem_pub)) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
/* allocate buffer for concatenation of KEM key and ECDH shared key */
/* the buffer will be hashed and the result is the shared secret */
if ((buf = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
/* allocate space for encrypted KEM key and ECDH pub key */
if ((server_blob = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
/* generate and encrypt KEM key with client key */
arc4random_buf(rnd, sizeof(rnd));
enc = libcrux_ml_kem_mlkem768_portable_encapsulate(&mlkem_pub, rnd);
/* generate ECDH key pair, store server pubkey after ciphertext */
kexc25519_keygen(server_key, server_pub);
if ((r = sshbuf_put(buf, enc.snd, sizeof(enc.snd))) != 0 ||
(r = sshbuf_put(server_blob, enc.fst.value, sizeof(enc.fst.value))) != 0 ||
(r = sshbuf_put(server_blob, server_pub, sizeof(server_pub))) != 0)
goto out;
/* append ECDH shared key */
client_pub += crypto_kem_mlkem768_PUBLICKEYBYTES;
if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 1)) < 0)
goto out;
if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
goto out;
#ifdef DEBUG_KEXECDH
dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
dump_digest("server cipher text:",
enc.fst.value, sizeof(enc.fst.value));
dump_digest("server kem key:", enc.snd, sizeof(enc.snd));
dump_digest("concatenation of KEM key and ECDH shared key:",
sshbuf_ptr(buf), sshbuf_len(buf));
#endif
/* string-encoded hash is resulting shared secret */
sshbuf_reset(buf);
if ((r = sshbuf_put_string(buf, hash,
ssh_digest_bytes(kex->hash_alg))) != 0)
goto out;
#ifdef DEBUG_KEXECDH
dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
#endif
/* success */
r = 0;
*server_blobp = server_blob;
*shared_secretp = buf;
server_blob = NULL;
buf = NULL;
out:
explicit_bzero(hash, sizeof(hash));
explicit_bzero(server_key, sizeof(server_key));
explicit_bzero(rnd, sizeof(rnd));
explicit_bzero(&enc, sizeof(enc));
sshbuf_free(server_blob);
sshbuf_free(buf);
return r;
}
int
kex_kem_mlkem768x25519_dec(struct kex *kex,
const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
{
struct sshbuf *buf = NULL;
u_char mlkem_key[crypto_kem_mlkem768_BYTES];
const u_char *ciphertext, *server_pub;
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t need;
int r;
struct libcrux_mlkem768_sk mlkem_priv;
struct libcrux_mlkem768_ciphertext mlkem_ciphertext;
*shared_secretp = NULL;
memset(&mlkem_priv, 0, sizeof(mlkem_priv));
memset(&mlkem_ciphertext, 0, sizeof(mlkem_ciphertext));
need = crypto_kem_mlkem768_CIPHERTEXTBYTES + CURVE25519_SIZE;
if (sshbuf_len(server_blob) != need) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
ciphertext = sshbuf_ptr(server_blob);
server_pub = ciphertext + crypto_kem_mlkem768_CIPHERTEXTBYTES;
/* hash concatenation of KEM key and ECDH shared key */
if ((buf = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
memcpy(mlkem_priv.value, kex->mlkem768_client_key,
sizeof(kex->mlkem768_client_key));
memcpy(mlkem_ciphertext.value, ciphertext,
sizeof(mlkem_ciphertext.value));
#ifdef DEBUG_KEXECDH
dump_digest("server cipher text:", mlkem_ciphertext.value,
sizeof(mlkem_ciphertext.value));
dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
#endif
libcrux_ml_kem_mlkem768_portable_decapsulate(&mlkem_priv,
&mlkem_ciphertext, mlkem_key);
if ((r = sshbuf_put(buf, mlkem_key, sizeof(mlkem_key))) != 0)
goto out;
if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
buf, 1)) < 0)
goto out;
if ((r = ssh_digest_buffer(kex->hash_alg, buf,
hash, sizeof(hash))) != 0)
goto out;
#ifdef DEBUG_KEXECDH
dump_digest("client kem key:", mlkem_key, sizeof(mlkem_key));
dump_digest("concatenation of KEM key and ECDH shared key:",
sshbuf_ptr(buf), sshbuf_len(buf));
#endif
sshbuf_reset(buf);
if ((r = sshbuf_put_string(buf, hash,
ssh_digest_bytes(kex->hash_alg))) != 0)
goto out;
#ifdef DEBUG_KEXECDH
dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
#endif
/* success */
r = 0;
*shared_secretp = buf;
buf = NULL;
out:
explicit_bzero(hash, sizeof(hash));
explicit_bzero(&mlkem_priv, sizeof(mlkem_priv));
explicit_bzero(&mlkem_ciphertext, sizeof(mlkem_ciphertext));
explicit_bzero(mlkem_key, sizeof(mlkem_key));
sshbuf_free(buf);
return r;
}
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