kexmlkem768x25519.c

   1 /* $OpenBSD: kexmlkem768x25519.c,v 1.2 2024/10/27 02:06:59 djm Exp $ */
   2 /*
   3  * Copyright (c) 2023 Markus Friedl.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "includes.h"
  27
  28 #include <sys/types.h>
  29
  30 #include <stdio.h>
  31 #ifdef HAVE_STDINT_H
  32 #include <stdint.h>
  33 #endif
  34 #include <stdbool.h>
  35 #include <string.h>
  36 #include <signal.h>
  37 #ifdef HAVE_ENDIAN_H
  38 # include <endian.h>
  39 #endif
  40
  41 #include "sshkey.h"
  42 #include "kex.h"
  43 #include "sshbuf.h"
  44 #include "digest.h"
  45 #include "ssherr.h"
  46 #include "log.h"
  47
  48 #ifdef USE_MLKEM768X25519
  49
  50 #include "libcrux_mlkem768_sha3.h"
  51
  52 int
  53 kex_kem_mlkem768x25519_keypair(struct kex *kex)
  54 {
  55         struct sshbuf *buf = NULL;
  56         u_char rnd[LIBCRUX_ML_KEM_KEY_PAIR_PRNG_LEN], *cp = NULL;
  57         size_t need;
  58         int r = SSH_ERR_INTERNAL_ERROR;
  59         struct libcrux_mlkem768_keypair keypair;
  60
  61         if ((buf = sshbuf_new()) == NULL)
  62                 return SSH_ERR_ALLOC_FAIL;
  63         need = crypto_kem_mlkem768_PUBLICKEYBYTES + CURVE25519_SIZE;
  64         if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
  65                 goto out;
  66         arc4random_buf(rnd, sizeof(rnd));
  67         keypair = libcrux_ml_kem_mlkem768_portable_generate_key_pair(rnd);
  68         memcpy(cp, keypair.pk.value, crypto_kem_mlkem768_PUBLICKEYBYTES);
  69         memcpy(kex->mlkem768_client_key, keypair.sk.value,
  70             sizeof(kex->mlkem768_client_key));
  71 #ifdef DEBUG_KEXECDH
  72         dump_digest("client public key mlkem768:", cp,
  73             crypto_kem_mlkem768_PUBLICKEYBYTES);
  74 #endif
  75         cp += crypto_kem_mlkem768_PUBLICKEYBYTES;
  76         kexc25519_keygen(kex->c25519_client_key, cp);
  77 #ifdef DEBUG_KEXECDH
  78         dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
  79 #endif
  80         /* success */
  81         r = 0;
  82         kex->client_pub = buf;
  83         buf = NULL;
  84  out:
  85         explicit_bzero(&keypair, sizeof(keypair));
  86         explicit_bzero(rnd, sizeof(rnd));
  87         sshbuf_free(buf);
  88         return r;
  89 }
  90
  91 int
  92 kex_kem_mlkem768x25519_enc(struct kex *kex,
  93    const struct sshbuf *client_blob, struct sshbuf **server_blobp,
  94    struct sshbuf **shared_secretp)
  95 {
  96         struct sshbuf *server_blob = NULL;
  97         struct sshbuf *buf = NULL;
  98         const u_char *client_pub;
  99         u_char rnd[LIBCRUX_ML_KEM_ENC_PRNG_LEN];
 100         u_char server_pub[CURVE25519_SIZE], server_key[CURVE25519_SIZE];
 101         u_char hash[SSH_DIGEST_MAX_LENGTH];
 102         size_t need;
 103         int r = SSH_ERR_INTERNAL_ERROR;
 104         struct libcrux_mlkem768_enc_result enc;
 105         struct libcrux_mlkem768_pk mlkem_pub;
 106
 107         *server_blobp = NULL;
 108         *shared_secretp = NULL;
 109         memset(&mlkem_pub, 0, sizeof(mlkem_pub));
 110
 111         /* client_blob contains both KEM and ECDH client pubkeys */
 112         need = crypto_kem_mlkem768_PUBLICKEYBYTES + CURVE25519_SIZE;
 113         if (sshbuf_len(client_blob) != need) {
 114                 r = SSH_ERR_SIGNATURE_INVALID;
 115                 goto out;
 116         }
 117         client_pub = sshbuf_ptr(client_blob);
 118 #ifdef DEBUG_KEXECDH
 119         dump_digest("client public key mlkem768:", client_pub,
 120             crypto_kem_mlkem768_PUBLICKEYBYTES);
 121         dump_digest("client public key 25519:",
 122             client_pub + crypto_kem_mlkem768_PUBLICKEYBYTES,
 123             CURVE25519_SIZE);
 124 #endif
 125         /* check public key validity */
 126         memcpy(mlkem_pub.value, client_pub, crypto_kem_mlkem768_PUBLICKEYBYTES);
 127         if (!libcrux_ml_kem_mlkem768_portable_validate_public_key(&mlkem_pub)) {
 128                 r = SSH_ERR_SIGNATURE_INVALID;
 129                 goto out;
 130         }
 131
 132         /* allocate buffer for concatenation of KEM key and ECDH shared key */
 133         /* the buffer will be hashed and the result is the shared secret */
 134         if ((buf = sshbuf_new()) == NULL) {
 135                 r = SSH_ERR_ALLOC_FAIL;
 136                 goto out;
 137         }
 138         /* allocate space for encrypted KEM key and ECDH pub key */
 139         if ((server_blob = sshbuf_new()) == NULL) {
 140                 r = SSH_ERR_ALLOC_FAIL;
 141                 goto out;
 142         }
 143         /* generate and encrypt KEM key with client key */
 144         arc4random_buf(rnd, sizeof(rnd));
 145         enc = libcrux_ml_kem_mlkem768_portable_encapsulate(&mlkem_pub, rnd);
 146         /* generate ECDH key pair, store server pubkey after ciphertext */
 147         kexc25519_keygen(server_key, server_pub);
 148         if ((r = sshbuf_put(buf, enc.snd, sizeof(enc.snd))) != 0 ||
 149             (r = sshbuf_put(server_blob, enc.fst.value, sizeof(enc.fst.value))) != 0 ||
 150             (r = sshbuf_put(server_blob, server_pub, sizeof(server_pub))) != 0)
 151                 goto out;
 152         /* append ECDH shared key */
 153         client_pub += crypto_kem_mlkem768_PUBLICKEYBYTES;
 154         if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 1)) < 0)
 155                 goto out;
 156         if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
 157                 goto out;
 158 #ifdef DEBUG_KEXECDH
 159         dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
 160         dump_digest("server cipher text:",
 161             enc.fst.value, sizeof(enc.fst.value));
 162         dump_digest("server kem key:", enc.snd, sizeof(enc.snd));
 163         dump_digest("concatenation of KEM key and ECDH shared key:",
 164             sshbuf_ptr(buf), sshbuf_len(buf));
 165 #endif
 166         /* string-encoded hash is resulting shared secret */
 167         sshbuf_reset(buf);
 168         if ((r = sshbuf_put_string(buf, hash,
 169             ssh_digest_bytes(kex->hash_alg))) != 0)
 170                 goto out;
 171 #ifdef DEBUG_KEXECDH
 172         dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
 173 #endif
 174         /* success */
 175         r = 0;
 176         *server_blobp = server_blob;
 177         *shared_secretp = buf;
 178         server_blob = NULL;
 179         buf = NULL;
 180  out:
 181         explicit_bzero(hash, sizeof(hash));
 182         explicit_bzero(server_key, sizeof(server_key));
 183         explicit_bzero(rnd, sizeof(rnd));
 184         explicit_bzero(&enc, sizeof(enc));
 185         sshbuf_free(server_blob);
 186         sshbuf_free(buf);
 187         return r;
 188 }
 189
 190 int
 191 kex_kem_mlkem768x25519_dec(struct kex *kex,
 192     const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
 193 {
 194         struct sshbuf *buf = NULL;
 195         u_char mlkem_key[crypto_kem_mlkem768_BYTES];
 196         const u_char *ciphertext, *server_pub;
 197         u_char hash[SSH_DIGEST_MAX_LENGTH];
 198         size_t need;
 199         int r;
 200         struct libcrux_mlkem768_sk mlkem_priv;
 201         struct libcrux_mlkem768_ciphertext mlkem_ciphertext;
 202
 203         *shared_secretp = NULL;
 204         memset(&mlkem_priv, 0, sizeof(mlkem_priv));
 205         memset(&mlkem_ciphertext, 0, sizeof(mlkem_ciphertext));
 206
 207         need = crypto_kem_mlkem768_CIPHERTEXTBYTES + CURVE25519_SIZE;
 208         if (sshbuf_len(server_blob) != need) {
 209                 r = SSH_ERR_SIGNATURE_INVALID;
 210                 goto out;
 211         }
 212         ciphertext = sshbuf_ptr(server_blob);
 213         server_pub = ciphertext + crypto_kem_mlkem768_CIPHERTEXTBYTES;
 214         /* hash concatenation of KEM key and ECDH shared key */
 215         if ((buf = sshbuf_new()) == NULL) {
 216                 r = SSH_ERR_ALLOC_FAIL;
 217                 goto out;
 218         }
 219         memcpy(mlkem_priv.value, kex->mlkem768_client_key,
 220             sizeof(kex->mlkem768_client_key));
 221         memcpy(mlkem_ciphertext.value, ciphertext,
 222             sizeof(mlkem_ciphertext.value));
 223 #ifdef DEBUG_KEXECDH
 224         dump_digest("server cipher text:", mlkem_ciphertext.value,
 225             sizeof(mlkem_ciphertext.value));
 226         dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
 227 #endif
 228         libcrux_ml_kem_mlkem768_portable_decapsulate(&mlkem_priv,
 229             &mlkem_ciphertext, mlkem_key);
 230         if ((r = sshbuf_put(buf, mlkem_key, sizeof(mlkem_key))) != 0)
 231                 goto out;
 232         if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
 233             buf, 1)) < 0)
 234                 goto out;
 235         if ((r = ssh_digest_buffer(kex->hash_alg, buf,
 236             hash, sizeof(hash))) != 0)
 237                 goto out;
 238 #ifdef DEBUG_KEXECDH
 239         dump_digest("client kem key:", mlkem_key, sizeof(mlkem_key));
 240         dump_digest("concatenation of KEM key and ECDH shared key:",
 241             sshbuf_ptr(buf), sshbuf_len(buf));
 242 #endif
 243         sshbuf_reset(buf);
 244         if ((r = sshbuf_put_string(buf, hash,
 245             ssh_digest_bytes(kex->hash_alg))) != 0)
 246                 goto out;
 247 #ifdef DEBUG_KEXECDH
 248         dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
 249 #endif
 250         /* success */
 251         r = 0;
 252         *shared_secretp = buf;
 253         buf = NULL;
 254  out:
 255         explicit_bzero(hash, sizeof(hash));
 256         explicit_bzero(&mlkem_priv, sizeof(mlkem_priv));
 257         explicit_bzero(&mlkem_ciphertext, sizeof(mlkem_ciphertext));
 258         explicit_bzero(mlkem_key, sizeof(mlkem_key));
 259         sshbuf_free(buf);
 260         return r;
 261 }
 262 #else /* USE_MLKEM768X25519 */
 263 int
 264 kex_kem_mlkem768x25519_keypair(struct kex *kex)
 265 {
 266         return SSH_ERR_SIGN_ALG_UNSUPPORTED;
 267 }
 268
 269 int
 270 kex_kem_mlkem768x25519_enc(struct kex *kex,
 271    const struct sshbuf *client_blob, struct sshbuf **server_blobp,
 272    struct sshbuf **shared_secretp)
 273 {
 274         return SSH_ERR_SIGN_ALG_UNSUPPORTED;
 275 }
 276
 277 int
 278 kex_kem_mlkem768x25519_dec(struct kex *kex,
 279     const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
 280 {
 281         return SSH_ERR_SIGN_ALG_UNSUPPORTED;
 282 }
 283 #endif /* USE_MLKEM768X25519 */