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