1/* $OpenBSD: kexgexc.c,v 1.38 2021/12/19 22:08:06 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 56static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *); 57static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *); 58 59int 60kexgex_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 (ssh->compat & 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 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); 87 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, 88 &input_kex_dh_gex_group); 89 r = 0; 90 out: 91 return r; 92} 93 94static int 95input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh) 96{ 97 struct kex *kex = ssh->kex; 98 BIGNUM *p = NULL, *g = NULL; 99 const BIGNUM *pub_key; 100 int r, bits; 101 102 debug("SSH2_MSG_KEX_DH_GEX_GROUP received"); 103 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, &kex_protocol_error); 104 105 if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 || 106 (r = sshpkt_get_bignum2(ssh, &g)) != 0 || 107 (r = sshpkt_get_end(ssh)) != 0) 108 goto out; 109 if ((bits = BN_num_bits(p)) < 0 || 110 (u_int)bits < kex->min || (u_int)bits > kex->max) { 111 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 112 goto out; 113 } 114 if ((kex->dh = dh_new_group(g, p)) == NULL) { 115 r = SSH_ERR_ALLOC_FAIL; 116 goto out; 117 } 118 p = g = NULL; /* belong to kex->dh now */ 119 120 /* generate and send 'e', client DH public key */ 121 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 122 goto out; 123 DH_get0_key(kex->dh, &pub_key, NULL); 124 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 || 125 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || 126 (r = sshpkt_send(ssh)) != 0) 127 goto out; 128 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 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 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); 136 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply); 137 r = 0; 138out: 139 BN_clear_free(p); 140 BN_clear_free(g); 141 return r; 142} 143 144static int 145input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh) 146{ 147 struct kex *kex = ssh->kex; 148 BIGNUM *dh_server_pub = NULL; 149 const BIGNUM *pub_key, *dh_p, *dh_g; 150 struct sshbuf *shared_secret = NULL; 151 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; 152 struct sshkey *server_host_key = NULL; 153 u_char *signature = NULL; 154 u_char hash[SSH_DIGEST_MAX_LENGTH]; 155 size_t slen, hashlen; 156 int r; 157 158 debug("SSH2_MSG_KEX_DH_GEX_REPLY received"); 159 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &kex_protocol_error); 160 161 /* key, cert */ 162 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 163 goto out; 164 /* sshkey_fromb() consumes its buffer, so make a copy */ 165 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 166 r = SSH_ERR_ALLOC_FAIL; 167 goto out; 168 } 169 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 || 170 (r = kex_verify_host_key(ssh, server_host_key)) != 0) 171 goto out; 172 /* DH parameter f, server public DH key, signed H */ 173 if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 || 174 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 175 (r = sshpkt_get_end(ssh)) != 0) 176 goto out; 177 if ((shared_secret = sshbuf_new()) == NULL) { 178 r = SSH_ERR_ALLOC_FAIL; 179 goto out; 180 } 181 if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0) 182 goto out; 183 if (ssh->compat & SSH_OLD_DHGEX) 184 kex->min = kex->max = -1; 185 186 /* calc and verify H */ 187 DH_get0_key(kex->dh, &pub_key, NULL); 188 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 189 hashlen = sizeof(hash); 190 if ((r = kexgex_hash( 191 kex->hash_alg, 192 kex->client_version, 193 kex->server_version, 194 kex->my, 195 kex->peer, 196 server_host_key_blob, 197 kex->min, kex->nbits, kex->max, 198 dh_p, dh_g, 199 pub_key, 200 dh_server_pub, 201 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 202 hash, &hashlen)) != 0) 203 goto out; 204 205 if ((r = sshkey_verify(server_host_key, signature, slen, hash, 206 hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0) 207 goto out; 208 209 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 210 (r = kex_send_newkeys(ssh)) != 0) 211 goto out; 212 213 /* save initial signature and hostkey */ 214 if ((kex->flags & KEX_INITIAL) != 0) { 215 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) { 216 r = SSH_ERR_INTERNAL_ERROR; 217 goto out; 218 } 219 if ((kex->initial_sig = sshbuf_new()) == NULL) { 220 r = SSH_ERR_ALLOC_FAIL; 221 goto out; 222 } 223 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0) 224 goto out; 225 kex->initial_hostkey = server_host_key; 226 server_host_key = NULL; 227 } 228 /* success */ 229 out: 230 explicit_bzero(hash, sizeof(hash)); 231 DH_free(kex->dh); 232 kex->dh = NULL; 233 BN_clear_free(dh_server_pub); 234 sshbuf_free(shared_secret); 235 sshkey_free(server_host_key); 236 sshbuf_free(tmp); 237 sshbuf_free(server_host_key_blob); 238 free(signature); 239 return r; 240} 241#endif /* WITH_OPENSSL */ 242