1 /* $OpenBSD: kexgexc.c,v 1.34 2019/01/23 00:30:41 djm Exp $ */ 2 /* 3 * Copyright (c) 2000 Niels Provos. All rights reserved. 4 * Copyright (c) 2001 Markus Friedl. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27 #include "includes.h" 28 29 #ifdef WITH_OPENSSL 30 31 #include <sys/types.h> 32 33 #include <openssl/dh.h> 34 35 #include <stdarg.h> 36 #include <stdio.h> 37 #include <string.h> 38 #include <signal.h> 39 40 #include "openbsd-compat/openssl-compat.h" 41 42 #include "sshkey.h" 43 #include "cipher.h" 44 #include "digest.h" 45 #include "kex.h" 46 #include "log.h" 47 #include "packet.h" 48 #include "dh.h" 49 #include "ssh2.h" 50 #include "compat.h" 51 #include "dispatch.h" 52 #include "ssherr.h" 53 #include "sshbuf.h" 54 #include "misc.h" 55 56 static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *); 57 static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *); 58 59 int 60 kexgex_client(struct ssh *ssh) 61 { 62 struct kex *kex = ssh->kex; 63 int r; 64 u_int nbits; 65 66 nbits = dh_estimate(kex->dh_need * 8); 67 68 kex->min = DH_GRP_MIN; 69 kex->max = DH_GRP_MAX; 70 kex->nbits = nbits; 71 if (datafellows & SSH_BUG_DHGEX_LARGE) 72 kex->nbits = MINIMUM(kex->nbits, 4096); 73 /* New GEX request */ 74 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 || 75 (r = sshpkt_put_u32(ssh, kex->min)) != 0 || 76 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 || 77 (r = sshpkt_put_u32(ssh, kex->max)) != 0 || 78 (r = sshpkt_send(ssh)) != 0) 79 goto out; 80 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent", 81 kex->min, kex->nbits, kex->max); 82 #ifdef DEBUG_KEXDH 83 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 84 kex->min, kex->nbits, kex->max); 85 #endif 86 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, 87 &input_kex_dh_gex_group); 88 r = 0; 89 out: 90 return r; 91 } 92 93 static int 94 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh) 95 { 96 struct kex *kex = ssh->kex; 97 BIGNUM *p = NULL, *g = NULL; 98 const BIGNUM *pub_key; 99 int r, bits; 100 101 debug("got SSH2_MSG_KEX_DH_GEX_GROUP"); 102 103 if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 || 104 (r = sshpkt_get_bignum2(ssh, &g)) != 0 || 105 (r = sshpkt_get_end(ssh)) != 0) 106 goto out; 107 if ((bits = BN_num_bits(p)) < 0 || 108 (u_int)bits < kex->min || (u_int)bits > kex->max) { 109 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 110 goto out; 111 } 112 if ((kex->dh = dh_new_group(g, p)) == NULL) { 113 r = SSH_ERR_ALLOC_FAIL; 114 goto out; 115 } 116 p = g = NULL; /* belong to kex->dh now */ 117 118 /* generate and send 'e', client DH public key */ 119 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 120 goto out; 121 DH_get0_key(kex->dh, &pub_key, NULL); 122 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 || 123 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || 124 (r = sshpkt_send(ssh)) != 0) 125 goto out; 126 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 127 #ifdef DEBUG_KEXDH 128 DHparams_print_fp(stderr, kex->dh); 129 fprintf(stderr, "pub= "); 130 BN_print_fp(stderr, pub_key); 131 fprintf(stderr, "\n"); 132 #endif 133 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL); 134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply); 135 r = 0; 136 out: 137 BN_clear_free(p); 138 BN_clear_free(g); 139 return r; 140 } 141 142 static int 143 input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh) 144 { 145 struct kex *kex = ssh->kex; 146 BIGNUM *dh_server_pub = NULL; 147 const BIGNUM *pub_key, *dh_p, *dh_g; 148 struct sshbuf *shared_secret = NULL; 149 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; 150 struct sshkey *server_host_key = NULL; 151 u_char *signature = NULL; 152 u_char hash[SSH_DIGEST_MAX_LENGTH]; 153 size_t slen, hashlen; 154 int r; 155 156 debug("got SSH2_MSG_KEX_DH_GEX_REPLY"); 157 /* key, cert */ 158 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 159 goto out; 160 /* sshkey_fromb() consumes its buffer, so make a copy */ 161 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 162 r = SSH_ERR_ALLOC_FAIL; 163 goto out; 164 } 165 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 || 166 (r = kex_verify_host_key(ssh, server_host_key)) != 0) 167 goto out; 168 /* DH parameter f, server public DH key, signed H */ 169 if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 || 170 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 171 (r = sshpkt_get_end(ssh)) != 0) 172 goto out; 173 if ((shared_secret = sshbuf_new()) == NULL) { 174 r = SSH_ERR_ALLOC_FAIL; 175 goto out; 176 } 177 if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0) 178 goto out; 179 if (ssh->compat & SSH_OLD_DHGEX) 180 kex->min = kex->max = -1; 181 182 /* calc and verify H */ 183 DH_get0_key(kex->dh, &pub_key, NULL); 184 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 185 hashlen = sizeof(hash); 186 if ((r = kexgex_hash( 187 kex->hash_alg, 188 kex->client_version, 189 kex->server_version, 190 kex->my, 191 kex->peer, 192 server_host_key_blob, 193 kex->min, kex->nbits, kex->max, 194 dh_p, dh_g, 195 pub_key, 196 dh_server_pub, 197 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 198 hash, &hashlen)) != 0) 199 goto out; 200 201 if ((r = sshkey_verify(server_host_key, signature, slen, hash, 202 hashlen, kex->hostkey_alg, ssh->compat)) != 0) 203 goto out; 204 205 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 206 r = kex_send_newkeys(ssh); 207 out: 208 explicit_bzero(hash, sizeof(hash)); 209 DH_free(kex->dh); 210 kex->dh = NULL; 211 BN_clear_free(dh_server_pub); 212 sshbuf_free(shared_secret); 213 sshkey_free(server_host_key); 214 sshbuf_free(tmp); 215 sshbuf_free(server_host_key_blob); 216 free(signature); 217 return r; 218 } 219 #endif /* WITH_OPENSSL */ 220