1 /* $OpenBSD: kexgexc.c,v 1.35 2019/11/25 00:51:37 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 <sys/types.h> 28 29 #include <openssl/dh.h> 30 31 #include <stdio.h> 32 #include <string.h> 33 #include <signal.h> 34 35 #include "sshkey.h" 36 #include "cipher.h" 37 #include "digest.h" 38 #include "kex.h" 39 #include "log.h" 40 #include "packet.h" 41 #include "dh.h" 42 #include "ssh2.h" 43 #include "compat.h" 44 #include "dispatch.h" 45 #include "ssherr.h" 46 #include "sshbuf.h" 47 #include "misc.h" 48 49 static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *); 50 static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *); 51 52 int 53 kexgex_client(struct ssh *ssh) 54 { 55 struct kex *kex = ssh->kex; 56 int r; 57 u_int nbits; 58 59 nbits = dh_estimate(kex->dh_need * 8); 60 61 kex->min = DH_GRP_MIN; 62 kex->max = DH_GRP_MAX; 63 kex->nbits = nbits; 64 if (datafellows & SSH_BUG_DHGEX_LARGE) 65 kex->nbits = MINIMUM(kex->nbits, 4096); 66 /* New GEX request */ 67 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 || 68 (r = sshpkt_put_u32(ssh, kex->min)) != 0 || 69 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 || 70 (r = sshpkt_put_u32(ssh, kex->max)) != 0 || 71 (r = sshpkt_send(ssh)) != 0) 72 goto out; 73 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent", 74 kex->min, kex->nbits, kex->max); 75 #ifdef DEBUG_KEXDH 76 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 77 kex->min, kex->nbits, kex->max); 78 #endif 79 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, 80 &input_kex_dh_gex_group); 81 r = 0; 82 out: 83 return r; 84 } 85 86 static int 87 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh) 88 { 89 struct kex *kex = ssh->kex; 90 BIGNUM *p = NULL, *g = NULL; 91 const BIGNUM *pub_key; 92 int r, bits; 93 94 debug("got SSH2_MSG_KEX_DH_GEX_GROUP"); 95 96 if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 || 97 (r = sshpkt_get_bignum2(ssh, &g)) != 0 || 98 (r = sshpkt_get_end(ssh)) != 0) 99 goto out; 100 if ((bits = BN_num_bits(p)) < 0 || 101 (u_int)bits < kex->min || (u_int)bits > kex->max) { 102 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 103 goto out; 104 } 105 if ((kex->dh = dh_new_group(g, p)) == NULL) { 106 r = SSH_ERR_ALLOC_FAIL; 107 goto out; 108 } 109 p = g = NULL; /* belong to kex->dh now */ 110 111 /* generate and send 'e', client DH public key */ 112 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 113 goto out; 114 DH_get0_key(kex->dh, &pub_key, NULL); 115 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 || 116 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || 117 (r = sshpkt_send(ssh)) != 0) 118 goto out; 119 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 120 #ifdef DEBUG_KEXDH 121 DHparams_print_fp(stderr, kex->dh); 122 fprintf(stderr, "pub= "); 123 BN_print_fp(stderr, pub_key); 124 fprintf(stderr, "\n"); 125 #endif 126 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL); 127 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply); 128 r = 0; 129 out: 130 BN_clear_free(p); 131 BN_clear_free(g); 132 return r; 133 } 134 135 static int 136 input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh) 137 { 138 struct kex *kex = ssh->kex; 139 BIGNUM *dh_server_pub = NULL; 140 const BIGNUM *pub_key, *dh_p, *dh_g; 141 struct sshbuf *shared_secret = NULL; 142 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; 143 struct sshkey *server_host_key = NULL; 144 u_char *signature = NULL; 145 u_char hash[SSH_DIGEST_MAX_LENGTH]; 146 size_t slen, hashlen; 147 int r; 148 149 debug("got SSH2_MSG_KEX_DH_GEX_REPLY"); 150 /* key, cert */ 151 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 152 goto out; 153 /* sshkey_fromb() consumes its buffer, so make a copy */ 154 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 155 r = SSH_ERR_ALLOC_FAIL; 156 goto out; 157 } 158 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 || 159 (r = kex_verify_host_key(ssh, server_host_key)) != 0) 160 goto out; 161 /* DH parameter f, server public DH key, signed H */ 162 if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 || 163 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 164 (r = sshpkt_get_end(ssh)) != 0) 165 goto out; 166 if ((shared_secret = sshbuf_new()) == NULL) { 167 r = SSH_ERR_ALLOC_FAIL; 168 goto out; 169 } 170 if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0) 171 goto out; 172 if (ssh->compat & SSH_OLD_DHGEX) 173 kex->min = kex->max = -1; 174 175 /* calc and verify H */ 176 DH_get0_key(kex->dh, &pub_key, NULL); 177 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 178 hashlen = sizeof(hash); 179 if ((r = kexgex_hash( 180 kex->hash_alg, 181 kex->client_version, 182 kex->server_version, 183 kex->my, 184 kex->peer, 185 server_host_key_blob, 186 kex->min, kex->nbits, kex->max, 187 dh_p, dh_g, 188 pub_key, 189 dh_server_pub, 190 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 191 hash, &hashlen)) != 0) 192 goto out; 193 194 if ((r = sshkey_verify(server_host_key, signature, slen, hash, 195 hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0) 196 goto out; 197 198 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 199 r = kex_send_newkeys(ssh); 200 out: 201 explicit_bzero(hash, sizeof(hash)); 202 DH_free(kex->dh); 203 kex->dh = NULL; 204 BN_clear_free(dh_server_pub); 205 sshbuf_free(shared_secret); 206 sshkey_free(server_host_key); 207 sshbuf_free(tmp); 208 sshbuf_free(server_host_key_blob); 209 free(signature); 210 return r; 211 } 212