Annotation of src/usr.bin/ssh/kexsntrup761x25519.c, Revision 1.2
1.2 ! jsg 1: /* $OpenBSD: kexsntrup761x25519.c,v 1.1 2020/12/29 00:59:15 djm Exp $ */
1.1 djm 2: /*
3: * Copyright (c) 2019 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 <sys/types.h>
27:
28: #include <stdio.h>
29: #include <string.h>
30: #include <signal.h>
31:
32: #include "sshkey.h"
33: #include "kex.h"
34: #include "sshbuf.h"
35: #include "digest.h"
36: #include "ssherr.h"
37:
38: int
39: kex_kem_sntrup761x25519_keypair(struct kex *kex)
40: {
41: struct sshbuf *buf = NULL;
42: u_char *cp = NULL;
43: size_t need;
44: int r;
45:
46: if ((buf = sshbuf_new()) == NULL)
47: return SSH_ERR_ALLOC_FAIL;
48: need = crypto_kem_sntrup761_PUBLICKEYBYTES + CURVE25519_SIZE;
49: if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
50: goto out;
51: crypto_kem_sntrup761_keypair(cp, kex->sntrup761_client_key);
52: #ifdef DEBUG_KEXECDH
53: dump_digest("client public key sntrup761:", cp,
54: crypto_kem_sntrup761_PUBLICKEYBYTES);
55: #endif
56: cp += crypto_kem_sntrup761_PUBLICKEYBYTES;
57: kexc25519_keygen(kex->c25519_client_key, cp);
58: #ifdef DEBUG_KEXECDH
59: dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
60: #endif
61: kex->client_pub = buf;
62: buf = NULL;
63: out:
64: sshbuf_free(buf);
65: return r;
66: }
67:
68: int
69: kex_kem_sntrup761x25519_enc(struct kex *kex,
70: const struct sshbuf *client_blob, struct sshbuf **server_blobp,
71: struct sshbuf **shared_secretp)
72: {
73: struct sshbuf *server_blob = NULL;
74: struct sshbuf *buf = NULL;
75: const u_char *client_pub;
76: u_char *kem_key, *ciphertext, *server_pub;
77: u_char server_key[CURVE25519_SIZE];
78: u_char hash[SSH_DIGEST_MAX_LENGTH];
79: size_t need;
80: int r;
81:
82: *server_blobp = NULL;
83: *shared_secretp = NULL;
84:
85: /* client_blob contains both KEM and ECDH client pubkeys */
86: need = crypto_kem_sntrup761_PUBLICKEYBYTES + CURVE25519_SIZE;
87: if (sshbuf_len(client_blob) != need) {
88: r = SSH_ERR_SIGNATURE_INVALID;
89: goto out;
90: }
91: client_pub = sshbuf_ptr(client_blob);
92: #ifdef DEBUG_KEXECDH
93: dump_digest("client public key sntrup761:", client_pub,
94: crypto_kem_sntrup761_PUBLICKEYBYTES);
95: dump_digest("client public key 25519:",
96: client_pub + crypto_kem_sntrup761_PUBLICKEYBYTES,
97: CURVE25519_SIZE);
98: #endif
99: /* allocate buffer for concatenation of KEM key and ECDH shared key */
100: /* the buffer will be hashed and the result is the shared secret */
101: if ((buf = sshbuf_new()) == NULL) {
102: r = SSH_ERR_ALLOC_FAIL;
103: goto out;
104: }
105: if ((r = sshbuf_reserve(buf, crypto_kem_sntrup761_BYTES,
106: &kem_key)) != 0)
107: goto out;
108: /* allocate space for encrypted KEM key and ECDH pub key */
109: if ((server_blob = sshbuf_new()) == NULL) {
110: r = SSH_ERR_ALLOC_FAIL;
111: goto out;
112: }
113: need = crypto_kem_sntrup761_CIPHERTEXTBYTES + CURVE25519_SIZE;
114: if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0)
115: goto out;
116: /* generate and encrypt KEM key with client key */
117: crypto_kem_sntrup761_enc(ciphertext, kem_key, client_pub);
118: /* generate ECDH key pair, store server pubkey after ciphertext */
119: server_pub = ciphertext + crypto_kem_sntrup761_CIPHERTEXTBYTES;
120: kexc25519_keygen(server_key, server_pub);
121: /* append ECDH shared key */
122: client_pub += crypto_kem_sntrup761_PUBLICKEYBYTES;
123: if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 1)) < 0)
124: goto out;
125: if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
126: goto out;
127: #ifdef DEBUG_KEXECDH
128: dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
129: dump_digest("server cipher text:", ciphertext,
130: crypto_kem_sntrup761_CIPHERTEXTBYTES);
1.2 ! jsg 131: dump_digest("server kem key:", kem_key, crypto_kem_sntrup761_BYTES);
1.1 djm 132: dump_digest("concatenation of KEM key and ECDH shared key:",
133: sshbuf_ptr(buf), sshbuf_len(buf));
134: #endif
135: /* string-encoded hash is resulting shared secret */
136: sshbuf_reset(buf);
137: if ((r = sshbuf_put_string(buf, hash,
138: ssh_digest_bytes(kex->hash_alg))) != 0)
139: goto out;
140: #ifdef DEBUG_KEXECDH
141: dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
142: #endif
143: *server_blobp = server_blob;
144: *shared_secretp = buf;
145: server_blob = NULL;
146: buf = NULL;
147: out:
148: explicit_bzero(hash, sizeof(hash));
149: explicit_bzero(server_key, sizeof(server_key));
150: sshbuf_free(server_blob);
151: sshbuf_free(buf);
152: return r;
153: }
154:
155: int
156: kex_kem_sntrup761x25519_dec(struct kex *kex,
157: const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
158: {
159: struct sshbuf *buf = NULL;
160: u_char *kem_key = NULL;
161: const u_char *ciphertext, *server_pub;
162: u_char hash[SSH_DIGEST_MAX_LENGTH];
163: size_t need;
164: int r, decoded;
165:
166: *shared_secretp = NULL;
167:
168: need = crypto_kem_sntrup761_CIPHERTEXTBYTES + CURVE25519_SIZE;
169: if (sshbuf_len(server_blob) != need) {
170: r = SSH_ERR_SIGNATURE_INVALID;
171: goto out;
172: }
173: ciphertext = sshbuf_ptr(server_blob);
174: server_pub = ciphertext + crypto_kem_sntrup761_CIPHERTEXTBYTES;
175: #ifdef DEBUG_KEXECDH
176: dump_digest("server cipher text:", ciphertext,
177: crypto_kem_sntrup761_CIPHERTEXTBYTES);
178: dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
179: #endif
180: /* hash concatenation of KEM key and ECDH shared key */
181: if ((buf = sshbuf_new()) == NULL) {
182: r = SSH_ERR_ALLOC_FAIL;
183: goto out;
184: }
185: if ((r = sshbuf_reserve(buf, crypto_kem_sntrup761_BYTES,
186: &kem_key)) != 0)
187: goto out;
188: decoded = crypto_kem_sntrup761_dec(kem_key, ciphertext,
189: kex->sntrup761_client_key);
190: if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
191: buf, 1)) < 0)
192: goto out;
193: if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
194: goto out;
195: #ifdef DEBUG_KEXECDH
196: dump_digest("client kem key:", kem_key, crypto_kem_sntrup761_BYTES);
197: dump_digest("concatenation of KEM key and ECDH shared key:",
198: sshbuf_ptr(buf), sshbuf_len(buf));
199: #endif
200: sshbuf_reset(buf);
201: if ((r = sshbuf_put_string(buf, hash,
202: ssh_digest_bytes(kex->hash_alg))) != 0)
203: goto out;
204: #ifdef DEBUG_KEXECDH
205: dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
206: #endif
207: if (decoded != 0) {
208: r = SSH_ERR_SIGNATURE_INVALID;
209: goto out;
210: }
211: *shared_secretp = buf;
212: buf = NULL;
213: out:
214: explicit_bzero(hash, sizeof(hash));
215: sshbuf_free(buf);
216: return r;
217: }
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