1 /* $NetBSD: kexmlkem768x25519.c,v 1.4 2025/04/09 15:49:32 christos Exp $ */
2 /* $OpenBSD: kexmlkem768x25519.c,v 1.2 2024/10/27 02:06:59 djm Exp $ */
3
4 /*
5 * Copyright (c) 2023 Markus Friedl. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27 #include "includes.h"
28 __RCSID("$NetBSD: kexmlkem768x25519.c,v 1.4 2025/04/09 15:49:32 christos Exp $");
29
30 #include <sys/types.h>
31
32 #include <stdio.h>
33 #include <stdint.h>
34 #include <stdbool.h>
35 #include <string.h>
36 #include <signal.h>
37 #include <endian.h>
38
39 #include "sshkey.h"
40 #include "kex.h"
41 #include "sshbuf.h"
42 #include "digest.h"
43 #include "ssherr.h"
44 #include "log.h"
45
46 #include "libcrux_mlkem768_sha3.h"
47
48 int
kex_kem_mlkem768x25519_keypair(struct kex * kex)49 kex_kem_mlkem768x25519_keypair(struct kex *kex)
50 {
51 struct sshbuf *buf = NULL;
52 u_char rnd[LIBCRUX_ML_KEM_KEY_PAIR_PRNG_LEN], *cp = NULL;
53 size_t need;
54 int r = SSH_ERR_INTERNAL_ERROR;
55 struct libcrux_mlkem768_keypair keypair;
56
57 if ((buf = sshbuf_new()) == NULL)
58 return SSH_ERR_ALLOC_FAIL;
59 need = crypto_kem_mlkem768_PUBLICKEYBYTES + CURVE25519_SIZE;
60 if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
61 goto out;
62 arc4random_buf(rnd, sizeof(rnd));
63 keypair = libcrux_ml_kem_mlkem768_portable_generate_key_pair(rnd);
64 memcpy(cp, keypair.pk.value, crypto_kem_mlkem768_PUBLICKEYBYTES);
65 memcpy(kex->mlkem768_client_key, keypair.sk.value,
66 sizeof(kex->mlkem768_client_key));
67 #ifdef DEBUG_KEXECDH
68 dump_digest("client public key mlkem768:", cp,
69 crypto_kem_mlkem768_PUBLICKEYBYTES);
70 #endif
71 cp += crypto_kem_mlkem768_PUBLICKEYBYTES;
72 kexc25519_keygen(kex->c25519_client_key, cp);
73 #ifdef DEBUG_KEXECDH
74 dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
75 #endif
76 /* success */
77 r = 0;
78 kex->client_pub = buf;
79 buf = NULL;
80 out:
81 explicit_bzero(&keypair, sizeof(keypair));
82 explicit_bzero(rnd, sizeof(rnd));
83 sshbuf_free(buf);
84 return r;
85 }
86
87 int
kex_kem_mlkem768x25519_enc(struct kex * kex,const struct sshbuf * client_blob,struct sshbuf ** server_blobp,struct sshbuf ** shared_secretp)88 kex_kem_mlkem768x25519_enc(struct kex *kex,
89 const struct sshbuf *client_blob, struct sshbuf **server_blobp,
90 struct sshbuf **shared_secretp)
91 {
92 struct sshbuf *server_blob = NULL;
93 struct sshbuf *buf = NULL;
94 const u_char *client_pub;
95 u_char rnd[LIBCRUX_ML_KEM_ENC_PRNG_LEN];
96 u_char server_pub[CURVE25519_SIZE], server_key[CURVE25519_SIZE];
97 u_char hash[SSH_DIGEST_MAX_LENGTH];
98 size_t need;
99 int r = SSH_ERR_INTERNAL_ERROR;
100 struct libcrux_mlkem768_enc_result enc;
101 struct libcrux_mlkem768_pk mlkem_pub;
102
103 *server_blobp = NULL;
104 *shared_secretp = NULL;
105 memset(&mlkem_pub, 0, sizeof(mlkem_pub));
106
107 /* client_blob contains both KEM and ECDH client pubkeys */
108 need = crypto_kem_mlkem768_PUBLICKEYBYTES + CURVE25519_SIZE;
109 if (sshbuf_len(client_blob) != need) {
110 r = SSH_ERR_SIGNATURE_INVALID;
111 goto out;
112 }
113 client_pub = sshbuf_ptr(client_blob);
114 #ifdef DEBUG_KEXECDH
115 dump_digest("client public key mlkem768:", client_pub,
116 crypto_kem_mlkem768_PUBLICKEYBYTES);
117 dump_digest("client public key 25519:",
118 client_pub + crypto_kem_mlkem768_PUBLICKEYBYTES,
119 CURVE25519_SIZE);
120 #endif
121 /* check public key validity */
122 memcpy(mlkem_pub.value, client_pub, crypto_kem_mlkem768_PUBLICKEYBYTES);
123 if (!libcrux_ml_kem_mlkem768_portable_validate_public_key(&mlkem_pub)) {
124 r = SSH_ERR_SIGNATURE_INVALID;
125 goto out;
126 }
127
128 /* allocate buffer for concatenation of KEM key and ECDH shared key */
129 /* the buffer will be hashed and the result is the shared secret */
130 if ((buf = sshbuf_new()) == NULL) {
131 r = SSH_ERR_ALLOC_FAIL;
132 goto out;
133 }
134 /* allocate space for encrypted KEM key and ECDH pub key */
135 if ((server_blob = sshbuf_new()) == NULL) {
136 r = SSH_ERR_ALLOC_FAIL;
137 goto out;
138 }
139 /* generate and encrypt KEM key with client key */
140 arc4random_buf(rnd, sizeof(rnd));
141 enc = libcrux_ml_kem_mlkem768_portable_encapsulate(&mlkem_pub, rnd);
142 /* generate ECDH key pair, store server pubkey after ciphertext */
143 kexc25519_keygen(server_key, server_pub);
144 if ((r = sshbuf_put(buf, enc.snd, sizeof(enc.snd))) != 0 ||
145 (r = sshbuf_put(server_blob, enc.fst.value, sizeof(enc.fst.value))) != 0 ||
146 (r = sshbuf_put(server_blob, server_pub, sizeof(server_pub))) != 0)
147 goto out;
148 /* append ECDH shared key */
149 client_pub += crypto_kem_mlkem768_PUBLICKEYBYTES;
150 if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 1)) < 0)
151 goto out;
152 if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
153 goto out;
154 #ifdef DEBUG_KEXECDH
155 dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
156 dump_digest("server cipher text:",
157 enc.fst.value, sizeof(enc.fst.value));
158 dump_digest("server kem key:", enc.snd, sizeof(enc.snd));
159 dump_digest("concatenation of KEM key and ECDH shared key:",
160 sshbuf_ptr(buf), sshbuf_len(buf));
161 #endif
162 /* string-encoded hash is resulting shared secret */
163 sshbuf_reset(buf);
164 if ((r = sshbuf_put_string(buf, hash,
165 ssh_digest_bytes(kex->hash_alg))) != 0)
166 goto out;
167 #ifdef DEBUG_KEXECDH
168 dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
169 #endif
170 /* success */
171 r = 0;
172 *server_blobp = server_blob;
173 *shared_secretp = buf;
174 server_blob = NULL;
175 buf = NULL;
176 out:
177 explicit_bzero(hash, sizeof(hash));
178 explicit_bzero(server_key, sizeof(server_key));
179 explicit_bzero(rnd, sizeof(rnd));
180 explicit_bzero(&enc, sizeof(enc));
181 sshbuf_free(server_blob);
182 sshbuf_free(buf);
183 return r;
184 }
185
186 int
kex_kem_mlkem768x25519_dec(struct kex * kex,const struct sshbuf * server_blob,struct sshbuf ** shared_secretp)187 kex_kem_mlkem768x25519_dec(struct kex *kex,
188 const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
189 {
190 struct sshbuf *buf = NULL;
191 u_char mlkem_key[crypto_kem_mlkem768_BYTES];
192 const u_char *ciphertext, *server_pub;
193 u_char hash[SSH_DIGEST_MAX_LENGTH];
194 size_t need;
195 int r;
196 struct libcrux_mlkem768_sk mlkem_priv;
197 struct libcrux_mlkem768_ciphertext mlkem_ciphertext;
198
199 *shared_secretp = NULL;
200 memset(&mlkem_priv, 0, sizeof(mlkem_priv));
201 memset(&mlkem_ciphertext, 0, sizeof(mlkem_ciphertext));
202
203 need = crypto_kem_mlkem768_CIPHERTEXTBYTES + CURVE25519_SIZE;
204 if (sshbuf_len(server_blob) != need) {
205 r = SSH_ERR_SIGNATURE_INVALID;
206 goto out;
207 }
208 ciphertext = sshbuf_ptr(server_blob);
209 server_pub = ciphertext + crypto_kem_mlkem768_CIPHERTEXTBYTES;
210 /* hash concatenation of KEM key and ECDH shared key */
211 if ((buf = sshbuf_new()) == NULL) {
212 r = SSH_ERR_ALLOC_FAIL;
213 goto out;
214 }
215 memcpy(mlkem_priv.value, kex->mlkem768_client_key,
216 sizeof(kex->mlkem768_client_key));
217 memcpy(mlkem_ciphertext.value, ciphertext,
218 sizeof(mlkem_ciphertext.value));
219 #ifdef DEBUG_KEXECDH
220 dump_digest("server cipher text:", mlkem_ciphertext.value,
221 sizeof(mlkem_ciphertext.value));
222 dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
223 #endif
224 libcrux_ml_kem_mlkem768_portable_decapsulate(&mlkem_priv,
225 &mlkem_ciphertext, mlkem_key);
226 if ((r = sshbuf_put(buf, mlkem_key, sizeof(mlkem_key))) != 0)
227 goto out;
228 if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
229 buf, 1)) < 0)
230 goto out;
231 if ((r = ssh_digest_buffer(kex->hash_alg, buf,
232 hash, sizeof(hash))) != 0)
233 goto out;
234 #ifdef DEBUG_KEXECDH
235 dump_digest("client kem key:", mlkem_key, sizeof(mlkem_key));
236 dump_digest("concatenation of KEM key and ECDH shared key:",
237 sshbuf_ptr(buf), sshbuf_len(buf));
238 #endif
239 sshbuf_reset(buf);
240 if ((r = sshbuf_put_string(buf, hash,
241 ssh_digest_bytes(kex->hash_alg))) != 0)
242 goto out;
243 #ifdef DEBUG_KEXECDH
244 dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
245 #endif
246 /* success */
247 r = 0;
248 *shared_secretp = buf;
249 buf = NULL;
250 out:
251 explicit_bzero(hash, sizeof(hash));
252 explicit_bzero(&mlkem_priv, sizeof(mlkem_priv));
253 explicit_bzero(&mlkem_ciphertext, sizeof(mlkem_ciphertext));
254 explicit_bzero(mlkem_key, sizeof(mlkem_key));
255 sshbuf_free(buf);
256 return r;
257 }
258