1 /* $OpenBSD: kexgexs.c,v 1.42 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 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 #include "compat.h" 50 #ifdef GSSAPI 51 #include "ssh-gss.h" 52 #endif 53 #include "monitor_wrap.h" 54 #include "dispatch.h" 55 #include "ssherr.h" 56 #include "sshbuf.h" 57 #include "misc.h" 58 59 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); 60 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 61 62 int 63 kexgex_server(struct ssh *ssh) 64 { 65 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 66 &input_kex_dh_gex_request); 67 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 68 return 0; 69 } 70 71 static int 72 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 73 { 74 struct kex *kex = ssh->kex; 75 int r; 76 u_int min = 0, max = 0, nbits = 0; 77 const BIGNUM *dh_p, *dh_g; 78 79 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 80 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 81 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 82 (r = sshpkt_get_u32(ssh, &max)) != 0 || 83 (r = sshpkt_get_end(ssh)) != 0) 84 goto out; 85 kex->nbits = nbits; 86 kex->min = min; 87 kex->max = max; 88 min = MAXIMUM(DH_GRP_MIN, min); 89 max = MINIMUM(DH_GRP_MAX, max); 90 nbits = MAXIMUM(DH_GRP_MIN, nbits); 91 nbits = MINIMUM(DH_GRP_MAX, nbits); 92 93 if (kex->max < kex->min || kex->nbits < kex->min || 94 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 95 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 96 goto out; 97 } 98 99 /* Contact privileged parent */ 100 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 101 if (kex->dh == NULL) { 102 sshpkt_disconnect(ssh, "no matching DH grp found"); 103 r = SSH_ERR_ALLOC_FAIL; 104 goto out; 105 } 106 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 107 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 108 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 109 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || 110 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || 111 (r = sshpkt_send(ssh)) != 0) 112 goto out; 113 114 /* Compute our exchange value in parallel with the client */ 115 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 116 goto out; 117 118 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 119 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 120 r = 0; 121 out: 122 return r; 123 } 124 125 static int 126 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 127 { 128 struct kex *kex = ssh->kex; 129 BIGNUM *dh_client_pub = NULL; 130 const BIGNUM *pub_key, *dh_p, *dh_g; 131 struct sshbuf *shared_secret = NULL; 132 struct sshbuf *server_host_key_blob = NULL; 133 struct sshkey *server_host_public, *server_host_private; 134 u_char *signature = NULL; 135 u_char hash[SSH_DIGEST_MAX_LENGTH]; 136 size_t slen, hashlen; 137 int r; 138 139 if ((r = kex_load_hostkey(ssh, &server_host_private, 140 &server_host_public)) != 0) 141 goto out; 142 143 /* key, cert */ 144 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 || 145 (r = sshpkt_get_end(ssh)) != 0) 146 goto out; 147 if ((shared_secret = sshbuf_new()) == NULL) { 148 r = SSH_ERR_ALLOC_FAIL; 149 goto out; 150 } 151 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0) 152 goto out; 153 if ((server_host_key_blob = sshbuf_new()) == NULL) { 154 r = SSH_ERR_ALLOC_FAIL; 155 goto out; 156 } 157 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 158 goto out; 159 160 /* calc H */ 161 DH_get0_key(kex->dh, &pub_key, NULL); 162 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 163 hashlen = sizeof(hash); 164 if ((r = kexgex_hash( 165 kex->hash_alg, 166 kex->client_version, 167 kex->server_version, 168 kex->peer, 169 kex->my, 170 server_host_key_blob, 171 kex->min, kex->nbits, kex->max, 172 dh_p, dh_g, 173 dh_client_pub, 174 pub_key, 175 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 176 hash, &hashlen)) != 0) 177 goto out; 178 179 /* sign H */ 180 if ((r = kex->sign(ssh, server_host_private, server_host_public, 181 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0) 182 goto out; 183 184 /* send server hostkey, DH pubkey 'f' and signed H */ 185 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 186 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 187 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ 188 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 189 (r = sshpkt_send(ssh)) != 0) 190 goto out; 191 192 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 193 r = kex_send_newkeys(ssh); 194 out: 195 explicit_bzero(hash, sizeof(hash)); 196 DH_free(kex->dh); 197 kex->dh = NULL; 198 BN_clear_free(dh_client_pub); 199 sshbuf_free(shared_secret); 200 sshbuf_free(server_host_key_blob); 201 free(signature); 202 return r; 203 } 204 #endif /* WITH_OPENSSL */ 205