1/* $OpenBSD: kexgexs.c,v 1.47 2024/05/17 00:30:23 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 28#include <stdio.h> 29#include <string.h> 30#include <signal.h> 31 32#include <openssl/dh.h> 33 34#include "sshkey.h" 35#include "cipher.h" 36#include "digest.h" 37#include "kex.h" 38#include "log.h" 39#include "packet.h" 40#include "dh.h" 41#include "ssh2.h" 42#ifdef GSSAPI 43#include "ssh-gss.h" 44#endif 45#include "monitor_wrap.h" 46#include "dispatch.h" 47#include "ssherr.h" 48#include "sshbuf.h" 49#include "misc.h" 50 51static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); 52static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 53 54int 55kexgex_server(struct ssh *ssh) 56{ 57 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 58 &input_kex_dh_gex_request); 59 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 60 return 0; 61} 62 63static int 64input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 65{ 66 struct kex *kex = ssh->kex; 67 int r; 68 u_int min = 0, max = 0, nbits = 0; 69 const BIGNUM *dh_p, *dh_g; 70 71 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 72 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error); 73 74 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 75 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 76 (r = sshpkt_get_u32(ssh, &max)) != 0 || 77 (r = sshpkt_get_end(ssh)) != 0) 78 goto out; 79 kex->nbits = nbits; 80 kex->min = min; 81 kex->max = max; 82 min = MAXIMUM(DH_GRP_MIN, min); 83 max = MINIMUM(DH_GRP_MAX, max); 84 nbits = MAXIMUM(DH_GRP_MIN, nbits); 85 nbits = MINIMUM(DH_GRP_MAX, nbits); 86 87 if (kex->max < kex->min || kex->nbits < kex->min || 88 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 89 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 90 goto out; 91 } 92 93 /* Contact privileged parent */ 94 kex->dh = mm_choose_dh(min, nbits, max); 95 if (kex->dh == NULL) { 96 (void)sshpkt_disconnect(ssh, "no matching DH grp found"); 97 r = SSH_ERR_ALLOC_FAIL; 98 goto out; 99 } 100 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 101 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 102 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 103 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || 104 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || 105 (r = sshpkt_send(ssh)) != 0) 106 goto out; 107 108 /* Compute our exchange value in parallel with the client */ 109 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 110 goto out; 111 112 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 113 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 114 r = 0; 115 out: 116 return r; 117} 118 119static int 120input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 121{ 122 struct kex *kex = ssh->kex; 123 BIGNUM *dh_client_pub = NULL; 124 const BIGNUM *pub_key, *dh_p, *dh_g; 125 struct sshbuf *shared_secret = NULL; 126 struct sshbuf *server_host_key_blob = NULL; 127 struct sshkey *server_host_public, *server_host_private; 128 u_char *signature = NULL; 129 u_char hash[SSH_DIGEST_MAX_LENGTH]; 130 size_t slen, hashlen; 131 int r; 132 133 debug("SSH2_MSG_KEX_DH_GEX_INIT received"); 134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error); 135 136 if ((r = kex_load_hostkey(ssh, &server_host_private, 137 &server_host_public)) != 0) 138 goto out; 139 140 /* key, cert */ 141 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 || 142 (r = sshpkt_get_end(ssh)) != 0) 143 goto out; 144 if ((shared_secret = sshbuf_new()) == NULL) { 145 r = SSH_ERR_ALLOC_FAIL; 146 goto out; 147 } 148 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0) 149 goto out; 150 if ((server_host_key_blob = sshbuf_new()) == NULL) { 151 r = SSH_ERR_ALLOC_FAIL; 152 goto out; 153 } 154 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 155 goto out; 156 157 /* calc H */ 158 DH_get0_key(kex->dh, &pub_key, NULL); 159 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 160 hashlen = sizeof(hash); 161 if ((r = kexgex_hash( 162 kex->hash_alg, 163 kex->client_version, 164 kex->server_version, 165 kex->peer, 166 kex->my, 167 server_host_key_blob, 168 kex->min, kex->nbits, kex->max, 169 dh_p, dh_g, 170 dh_client_pub, 171 pub_key, 172 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 173 hash, &hashlen)) != 0) 174 goto out; 175 176 /* sign H */ 177 if ((r = kex->sign(ssh, server_host_private, server_host_public, 178 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0) 179 goto out; 180 181 /* send server hostkey, DH pubkey 'f' and signed H */ 182 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 183 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 184 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ 185 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 186 (r = sshpkt_send(ssh)) != 0) 187 goto out; 188 189 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 190 (r = kex_send_newkeys(ssh)) != 0) 191 goto out; 192 193 /* retain copy of hostkey used at initial KEX */ 194 if (kex->initial_hostkey == NULL && 195 (r = sshkey_from_private(server_host_public, 196 &kex->initial_hostkey)) != 0) 197 goto out; 198 /* success */ 199 out: 200 explicit_bzero(hash, sizeof(hash)); 201 DH_free(kex->dh); 202 kex->dh = NULL; 203 BN_clear_free(dh_client_pub); 204 sshbuf_free(shared_secret); 205 sshbuf_free(server_host_key_blob); 206 free(signature); 207 return r; 208} 209