1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
|
/* $OpenBSD: kexsntrup4591761x25519.c,v 1.1 2019/01/21 10:20:12 djm Exp $ */
/*
* Copyright (c) 2019 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 <string.h>
#include <signal.h>
#include "sshkey.h"
#include "kex.h"
#include "sshbuf.h"
#include "digest.h"
#include "ssherr.h"
int
kex_kem_sntrup4591761x25519_keypair(struct kex *kex)
{
struct sshbuf *buf = NULL;
u_char *cp = NULL;
size_t need;
int r;
if ((buf = sshbuf_new()) == NULL)
return SSH_ERR_ALLOC_FAIL;
need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE;
if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
goto out;
crypto_kem_sntrup4591761_keypair(cp, kex->sntrup4591761_client_key);
#ifdef DEBUG_KEXECDH
dump_digest("client public key sntrup4591761:", cp,
crypto_kem_sntrup4591761_PUBLICKEYBYTES);
#endif
cp += crypto_kem_sntrup4591761_PUBLICKEYBYTES;
kexc25519_keygen(kex->c25519_client_key, cp);
#ifdef DEBUG_KEXECDH
dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
#endif
kex->kem_client_pub = buf;
buf = NULL;
out:
sshbuf_free(buf);
return r;
}
int
kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob,
size_t pklen, struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
{
struct sshbuf *server_blob = NULL;
struct sshbuf *buf = NULL;
u_char *kem_key, *ciphertext, *server_pub;
u_char server_key[CURVE25519_SIZE];
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t need;
int r;
*server_blobp = NULL;
*shared_secretp = NULL;
/* pkblob contains both KEM and ECDH client pubkeys */
need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE;
if (pklen != need) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
#ifdef DEBUG_KEXECDH
dump_digest("client public key sntrup4591761:", pkblob,
crypto_kem_sntrup4591761_PUBLICKEYBYTES);
dump_digest("client public key 25519:",
pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, CURVE25519_SIZE);
#endif
/* 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;
}
if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES,
&kem_key)) != 0)
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;
}
need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE;
if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0)
goto out;
/* generate and encrypt KEM key with client key */
crypto_kem_sntrup4591761_enc(ciphertext, kem_key, pkblob);
/* generate ECDH key pair, store server pubkey after ciphertext */
server_pub = ciphertext + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
kexc25519_keygen(server_key, server_pub);
/* append ECDH shared key */
if ((r = kexc25519_shared_key_ext(server_key,
pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, 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:", ciphertext,
crypto_kem_sntrup4591761_CIPHERTEXTBYTES);
dump_digest("server kem key:", kem_key, sizeof(kem_key));
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
*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));
sshbuf_free(server_blob);
sshbuf_free(buf);
return r;
}
int
kex_kem_sntrup4591761x25519_dec(struct kex *kex, const u_char *pkblob,
size_t pklen, struct sshbuf **shared_secretp)
{
struct sshbuf *buf = NULL;
u_char *kem_key = NULL;
const u_char *ciphertext, *server_pub;
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t need;
int r, decoded;
*shared_secretp = NULL;
need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE;
if (pklen != need) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
ciphertext = pkblob;
server_pub = pkblob + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
#ifdef DEBUG_KEXECDH
dump_digest("server cipher text:", ciphertext,
crypto_kem_sntrup4591761_CIPHERTEXTBYTES);
dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
#endif
/* hash concatenation of KEM key and ECDH shared key */
if ((buf = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES,
&kem_key)) != 0)
goto out;
decoded = crypto_kem_sntrup4591761_dec(kem_key, ciphertext,
kex->sntrup4591761_client_key);
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:", kem_key, sizeof(kem_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
if (decoded != 0) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
*shared_secretp = buf;
buf = NULL;
out:
explicit_bzero(hash, sizeof(hash));
sshbuf_free(buf);
return r;
}
|
