/* $NetBSD: kexgexs.c,v 1.19.2.1 2023/12/25 12:31:04 martin Exp $ */ /* $OpenBSD: kexgexs.c,v 1.46 2023/03/29 01:07:48 dtucker Exp $ */ /* * Copyright (c) 2000 Niels Provos. All rights reserved. * Copyright (c) 2001 Markus Friedl. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "includes.h" __RCSID("$NetBSD: kexgexs.c,v 1.19.2.1 2023/12/25 12:31:04 martin Exp $"); #include /* MIN MAX */ #include #include #include #include #include "sshkey.h" #include "cipher.h" #include "digest.h" #include "kex.h" #include "log.h" #include "packet.h" #include "dh.h" #include "ssh2.h" #ifdef GSSAPI #include "ssh-gss.h" #endif #include "monitor_wrap.h" #include "dispatch.h" #include "ssherr.h" #include "sshbuf.h" #include "misc.h" static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); int kexgex_server(struct ssh *ssh) { ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &input_kex_dh_gex_request); debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); return 0; } static int input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) { struct kex *kex = ssh->kex; int r; u_int min = 0, max = 0, nbits = 0; const BIGNUM *dh_p, *dh_g; debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error); if ((r = sshpkt_get_u32(ssh, &min)) != 0 || (r = sshpkt_get_u32(ssh, &nbits)) != 0 || (r = sshpkt_get_u32(ssh, &max)) != 0 || (r = sshpkt_get_end(ssh)) != 0) goto out; kex->nbits = nbits; kex->min = min; kex->max = max; min = MAXIMUM(DH_GRP_MIN, min); max = MINIMUM(DH_GRP_MAX, max); nbits = MAXIMUM(DH_GRP_MIN, nbits); nbits = MINIMUM(DH_GRP_MAX, nbits); if (kex->max < kex->min || kex->nbits < kex->min || kex->max < kex->nbits || kex->max < DH_GRP_MIN) { r = SSH_ERR_DH_GEX_OUT_OF_RANGE; goto out; } /* Contact privileged parent */ kex->dh = PRIVSEP(choose_dh(min, nbits, max)); if (kex->dh == NULL) { (void)sshpkt_disconnect(ssh, "no matching DH grp found"); r = SSH_ERR_ALLOC_FAIL; goto out; } debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || (r = sshpkt_send(ssh)) != 0) goto out; /* Compute our exchange value in parallel with the client */ if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) goto out; debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); r = 0; out: return r; } static int input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) { struct kex *kex = ssh->kex; BIGNUM *dh_client_pub = NULL; const BIGNUM *pub_key, *dh_p, *dh_g; struct sshbuf *shared_secret = NULL; struct sshbuf *server_host_key_blob = NULL; struct sshkey *server_host_public, *server_host_private; u_char *signature = NULL; u_char hash[SSH_DIGEST_MAX_LENGTH]; size_t slen, hashlen; int r; debug("SSH2_MSG_KEX_DH_GEX_INIT received"); ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error); if ((r = kex_load_hostkey(ssh, &server_host_private, &server_host_public)) != 0) goto out; /* key, cert */ if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 || (r = sshpkt_get_end(ssh)) != 0) goto out; if ((shared_secret = sshbuf_new()) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto out; } if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0) goto out; if ((server_host_key_blob = sshbuf_new()) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto out; } if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) goto out; /* calc H */ DH_get0_key(kex->dh, &pub_key, NULL); DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); hashlen = sizeof(hash); if ((r = kexgex_hash( kex->hash_alg, kex->client_version, kex->server_version, kex->peer, kex->my, server_host_key_blob, kex->min, kex->nbits, kex->max, dh_p, dh_g, dh_client_pub, pub_key, sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), hash, &hashlen)) != 0) goto out; /* sign H */ if ((r = kex->sign(ssh, server_host_private, server_host_public, &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0) goto out; /* send server hostkey, DH pubkey 'f' and signed H */ if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ (r = sshpkt_put_string(ssh, signature, slen)) != 0 || (r = sshpkt_send(ssh)) != 0) goto out; if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || (r = kex_send_newkeys(ssh)) != 0) goto out; /* retain copy of hostkey used at initial KEX */ if (kex->initial_hostkey == NULL && (r = sshkey_from_private(server_host_public, &kex->initial_hostkey)) != 0) goto out; /* success */ out: explicit_bzero(hash, sizeof(hash)); DH_free(kex->dh); kex->dh = NULL; BN_clear_free(dh_client_pub); sshbuf_free(shared_secret); sshbuf_free(server_host_key_blob); free(signature); return r; }