1 /* $OpenBSD: kexdh.c,v 1.34 2020/12/04 02:29:25 djm Exp $ */ 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 "includes.h" 27 28 #ifdef WITH_OPENSSL 29 30 #include <sys/types.h> 31 32 #include <stdio.h> 33 #include <string.h> 34 #include <signal.h> 35 36 #include "openbsd-compat/openssl-compat.h" 37 #include <openssl/dh.h> 38 39 #include "sshkey.h" 40 #include "kex.h" 41 #include "sshbuf.h" 42 #include "digest.h" 43 #include "ssherr.h" 44 #include "dh.h" 45 #include "log.h" 46 47 int 48 kex_dh_keygen(struct kex *kex) 49 { 50 switch (kex->kex_type) { 51 case KEX_DH_GRP1_SHA1: 52 kex->dh = dh_new_group1(); 53 break; 54 case KEX_DH_GRP14_SHA1: 55 case KEX_DH_GRP14_SHA256: 56 kex->dh = dh_new_group14(); 57 break; 58 case KEX_DH_GRP16_SHA512: 59 kex->dh = dh_new_group16(); 60 break; 61 case KEX_DH_GRP18_SHA512: 62 kex->dh = dh_new_group18(); 63 break; 64 default: 65 return SSH_ERR_INVALID_ARGUMENT; 66 } 67 if (kex->dh == NULL) 68 return SSH_ERR_ALLOC_FAIL; 69 return (dh_gen_key(kex->dh, kex->we_need * 8)); 70 } 71 72 int 73 kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out) 74 { 75 BIGNUM *shared_secret = NULL; 76 u_char *kbuf = NULL; 77 size_t klen = 0; 78 int kout, r; 79 80 #ifdef DEBUG_KEXDH 81 fprintf(stderr, "dh_pub= "); 82 BN_print_fp(stderr, dh_pub); 83 fprintf(stderr, "\n"); 84 debug("bits %d", BN_num_bits(dh_pub)); 85 DHparams_print_fp(stderr, kex->dh); 86 fprintf(stderr, "\n"); 87 #endif 88 89 if (!dh_pub_is_valid(kex->dh, dh_pub)) { 90 r = SSH_ERR_MESSAGE_INCOMPLETE; 91 goto out; 92 } 93 klen = DH_size(kex->dh); 94 if ((kbuf = malloc(klen)) == NULL || 95 (shared_secret = BN_new()) == NULL) { 96 r = SSH_ERR_ALLOC_FAIL; 97 goto out; 98 } 99 if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 || 100 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 101 r = SSH_ERR_LIBCRYPTO_ERROR; 102 goto out; 103 } 104 #ifdef DEBUG_KEXDH 105 dump_digest("shared secret", kbuf, kout); 106 #endif 107 r = sshbuf_put_bignum2(out, shared_secret); 108 out: 109 freezero(kbuf, klen); 110 BN_clear_free(shared_secret); 111 return r; 112 } 113 114 int 115 kex_dh_keypair(struct kex *kex) 116 { 117 const BIGNUM *pub_key; 118 struct sshbuf *buf = NULL; 119 int r; 120 121 if ((r = kex_dh_keygen(kex)) != 0) 122 return r; 123 DH_get0_key(kex->dh, &pub_key, NULL); 124 if ((buf = sshbuf_new()) == NULL) 125 return SSH_ERR_ALLOC_FAIL; 126 if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 || 127 (r = sshbuf_get_u32(buf, NULL)) != 0) 128 goto out; 129 #ifdef DEBUG_KEXDH 130 DHparams_print_fp(stderr, kex->dh); 131 fprintf(stderr, "pub= "); 132 BN_print_fp(stderr, pub_key); 133 fprintf(stderr, "\n"); 134 #endif 135 kex->client_pub = buf; 136 buf = NULL; 137 out: 138 sshbuf_free(buf); 139 return r; 140 } 141 142 int 143 kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob, 144 struct sshbuf **server_blobp, struct sshbuf **shared_secretp) 145 { 146 const BIGNUM *pub_key; 147 struct sshbuf *server_blob = NULL; 148 int r; 149 150 *server_blobp = NULL; 151 *shared_secretp = NULL; 152 153 if ((r = kex_dh_keygen(kex)) != 0) 154 goto out; 155 DH_get0_key(kex->dh, &pub_key, NULL); 156 if ((server_blob = sshbuf_new()) == NULL) { 157 r = SSH_ERR_ALLOC_FAIL; 158 goto out; 159 } 160 if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 || 161 (r = sshbuf_get_u32(server_blob, NULL)) != 0) 162 goto out; 163 if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0) 164 goto out; 165 *server_blobp = server_blob; 166 server_blob = NULL; 167 out: 168 DH_free(kex->dh); 169 kex->dh = NULL; 170 sshbuf_free(server_blob); 171 return r; 172 } 173 174 int 175 kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob, 176 struct sshbuf **shared_secretp) 177 { 178 struct sshbuf *buf = NULL; 179 BIGNUM *dh_pub = NULL; 180 int r; 181 182 *shared_secretp = NULL; 183 184 if ((buf = sshbuf_new()) == NULL) { 185 r = SSH_ERR_ALLOC_FAIL; 186 goto out; 187 } 188 if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 || 189 (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0) 190 goto out; 191 sshbuf_reset(buf); 192 if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0) 193 goto out; 194 *shared_secretp = buf; 195 buf = NULL; 196 out: 197 BN_free(dh_pub); 198 DH_free(kex->dh); 199 kex->dh = NULL; 200 sshbuf_free(buf); 201 return r; 202 } 203 #endif /* WITH_OPENSSL */ 204