1 /* $OpenBSD: kexgexs.c,v 1.46 2023/03/29 01:07:48 dtucker 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 32 #include <stdarg.h> 33 #include <stdio.h> 34 #include <string.h> 35 #include <signal.h> 36 37 #include <openssl/dh.h> 38 39 #include "openbsd-compat/openssl-compat.h" 40 41 #include "sshkey.h" 42 #include "cipher.h" 43 #include "digest.h" 44 #include "kex.h" 45 #include "log.h" 46 #include "packet.h" 47 #include "dh.h" 48 #include "ssh2.h" 49 #ifdef GSSAPI 50 #include "ssh-gss.h" 51 #endif 52 #include "monitor_wrap.h" 53 #include "dispatch.h" 54 #include "ssherr.h" 55 #include "sshbuf.h" 56 #include "misc.h" 57 58 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); 59 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 60 61 int 62 kexgex_server(struct ssh *ssh) 63 { 64 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 65 &input_kex_dh_gex_request); 66 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 67 return 0; 68 } 69 70 static int 71 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 72 { 73 struct kex *kex = ssh->kex; 74 int r; 75 u_int min = 0, max = 0, nbits = 0; 76 const BIGNUM *dh_p, *dh_g; 77 78 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 79 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error); 80 81 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 82 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 83 (r = sshpkt_get_u32(ssh, &max)) != 0 || 84 (r = sshpkt_get_end(ssh)) != 0) 85 goto out; 86 kex->nbits = nbits; 87 kex->min = min; 88 kex->max = max; 89 min = MAXIMUM(DH_GRP_MIN, min); 90 max = MINIMUM(DH_GRP_MAX, max); 91 nbits = MAXIMUM(DH_GRP_MIN, nbits); 92 nbits = MINIMUM(DH_GRP_MAX, nbits); 93 94 if (kex->max < kex->min || kex->nbits < kex->min || 95 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 96 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 97 goto out; 98 } 99 100 /* Contact privileged parent */ 101 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 102 if (kex->dh == NULL) { 103 (void)sshpkt_disconnect(ssh, "no matching DH grp found"); 104 r = SSH_ERR_ALLOC_FAIL; 105 goto out; 106 } 107 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 108 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 109 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 110 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || 111 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || 112 (r = sshpkt_send(ssh)) != 0) 113 goto out; 114 115 /* Compute our exchange value in parallel with the client */ 116 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 117 goto out; 118 119 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 120 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 121 r = 0; 122 out: 123 return r; 124 } 125 126 static int 127 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 128 { 129 struct kex *kex = ssh->kex; 130 BIGNUM *dh_client_pub = NULL; 131 const BIGNUM *pub_key, *dh_p, *dh_g; 132 struct sshbuf *shared_secret = NULL; 133 struct sshbuf *server_host_key_blob = NULL; 134 struct sshkey *server_host_public, *server_host_private; 135 u_char *signature = NULL; 136 u_char hash[SSH_DIGEST_MAX_LENGTH]; 137 size_t slen, hashlen; 138 int r; 139 140 debug("SSH2_MSG_KEX_DH_GEX_INIT received"); 141 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error); 142 143 if ((r = kex_load_hostkey(ssh, &server_host_private, 144 &server_host_public)) != 0) 145 goto out; 146 147 /* key, cert */ 148 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 || 149 (r = sshpkt_get_end(ssh)) != 0) 150 goto out; 151 if ((shared_secret = sshbuf_new()) == NULL) { 152 r = SSH_ERR_ALLOC_FAIL; 153 goto out; 154 } 155 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0) 156 goto out; 157 if ((server_host_key_blob = sshbuf_new()) == NULL) { 158 r = SSH_ERR_ALLOC_FAIL; 159 goto out; 160 } 161 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 162 goto out; 163 164 /* calc H */ 165 DH_get0_key(kex->dh, &pub_key, NULL); 166 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 167 hashlen = sizeof(hash); 168 if ((r = kexgex_hash( 169 kex->hash_alg, 170 kex->client_version, 171 kex->server_version, 172 kex->peer, 173 kex->my, 174 server_host_key_blob, 175 kex->min, kex->nbits, kex->max, 176 dh_p, dh_g, 177 dh_client_pub, 178 pub_key, 179 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 180 hash, &hashlen)) != 0) 181 goto out; 182 183 /* sign H */ 184 if ((r = kex->sign(ssh, server_host_private, server_host_public, 185 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0) 186 goto out; 187 188 /* send server hostkey, DH pubkey 'f' and signed H */ 189 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 190 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 191 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ 192 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 193 (r = sshpkt_send(ssh)) != 0) 194 goto out; 195 196 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 197 (r = kex_send_newkeys(ssh)) != 0) 198 goto out; 199 200 /* retain copy of hostkey used at initial KEX */ 201 if (kex->initial_hostkey == NULL && 202 (r = sshkey_from_private(server_host_public, 203 &kex->initial_hostkey)) != 0) 204 goto out; 205 /* success */ 206 out: 207 explicit_bzero(hash, sizeof(hash)); 208 DH_free(kex->dh); 209 kex->dh = NULL; 210 BN_clear_free(dh_client_pub); 211 sshbuf_free(shared_secret); 212 sshbuf_free(server_host_key_blob); 213 free(signature); 214 return r; 215 } 216 #endif /* WITH_OPENSSL */ 217