/* $OpenBSD: kex.c,v 1.98 2014/02/02 03:44:31 djm Exp $ */ /* $FreeBSD$ */ /* * Copyright (c) 2000, 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" #include #include #include #include #include #include #include #include "xmalloc.h" #include "ssh2.h" #include "buffer.h" #include "packet.h" #include "compat.h" #include "cipher.h" #include "key.h" #include "kex.h" #include "log.h" #include "mac.h" #include "match.h" #include "dispatch.h" #include "monitor.h" #include "roaming.h" #include "digest.h" #if OPENSSL_VERSION_NUMBER >= 0x00907000L # if defined(HAVE_EVP_SHA256) # define evp_ssh_sha256 EVP_sha256 # else extern const EVP_MD *evp_ssh_sha256(void); # endif #endif /* prototype */ static void kex_kexinit_finish(Kex *); static void kex_choose_conf(Kex *); struct kexalg { char *name; int type; int ec_nid; int hash_alg; }; static const struct kexalg kexalgs[] = { { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 }, { KEX_DH14, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 }, { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 }, #ifdef HAVE_EVP_SHA256 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 }, #endif #ifdef OPENSSL_HAS_ECC { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2, NID_X9_62_prime256v1, SSH_DIGEST_SHA256 }, { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1, SSH_DIGEST_SHA384 }, # ifdef OPENSSL_HAS_NISTP521 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1, SSH_DIGEST_SHA512 }, # endif #endif { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 }, #ifdef HAVE_EVP_SHA256 { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 }, #endif { NULL, -1, -1, -1}, }; char * kex_alg_list(char sep) { char *ret = NULL; size_t nlen, rlen = 0; const struct kexalg *k; for (k = kexalgs; k->name != NULL; k++) { if (ret != NULL) ret[rlen++] = sep; nlen = strlen(k->name); ret = xrealloc(ret, 1, rlen + nlen + 2); memcpy(ret + rlen, k->name, nlen + 1); rlen += nlen; } return ret; } static const struct kexalg * kex_alg_by_name(const char *name) { const struct kexalg *k; for (k = kexalgs; k->name != NULL; k++) { if (strcmp(k->name, name) == 0) return k; } return NULL; } /* Validate KEX method name list */ int kex_names_valid(const char *names) { char *s, *cp, *p; if (names == NULL || strcmp(names, "") == 0) return 0; s = cp = xstrdup(names); for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) { if (kex_alg_by_name(p) == NULL) { error("Unsupported KEX algorithm \"%.100s\"", p); free(s); return 0; } } debug3("kex names ok: [%s]", names); free(s); return 1; } /* put algorithm proposal into buffer. */ #ifndef NONE_CIPHER_ENABLED static void #else /* Also used in sshconnect2.c. */ void #endif kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) { u_int i; buffer_clear(b); /* * add a dummy cookie, the cookie will be overwritten by * kex_send_kexinit(), each time a kexinit is set */ for (i = 0; i < KEX_COOKIE_LEN; i++) buffer_put_char(b, 0); for (i = 0; i < PROPOSAL_MAX; i++) buffer_put_cstring(b, proposal[i]); buffer_put_char(b, 0); /* first_kex_packet_follows */ buffer_put_int(b, 0); /* uint32 reserved */ } /* parse buffer and return algorithm proposal */ static char ** kex_buf2prop(Buffer *raw, int *first_kex_follows) { Buffer b; u_int i; char **proposal; proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); buffer_init(&b); buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); /* skip cookie */ for (i = 0; i < KEX_COOKIE_LEN; i++) buffer_get_char(&b); /* extract kex init proposal strings */ for (i = 0; i < PROPOSAL_MAX; i++) { proposal[i] = buffer_get_cstring(&b,NULL); debug2("kex_parse_kexinit: %s", proposal[i]); } /* first kex follows / reserved */ i = buffer_get_char(&b); if (first_kex_follows != NULL) *first_kex_follows = i; debug2("kex_parse_kexinit: first_kex_follows %d ", i); i = buffer_get_int(&b); debug2("kex_parse_kexinit: reserved %u ", i); buffer_free(&b); return proposal; } static void kex_prop_free(char **proposal) { u_int i; for (i = 0; i < PROPOSAL_MAX; i++) free(proposal[i]); free(proposal); } /* ARGSUSED */ static void kex_protocol_error(int type, u_int32_t seq, void *ctxt) { error("Hm, kex protocol error: type %d seq %u", type, seq); } static void kex_reset_dispatch(void) { dispatch_range(SSH2_MSG_TRANSPORT_MIN, SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); } void kex_finish(Kex *kex) { kex_reset_dispatch(); packet_start(SSH2_MSG_NEWKEYS); packet_send(); /* packet_write_wait(); */ debug("SSH2_MSG_NEWKEYS sent"); debug("expecting SSH2_MSG_NEWKEYS"); packet_read_expect(SSH2_MSG_NEWKEYS); packet_check_eom(); debug("SSH2_MSG_NEWKEYS received"); kex->done = 1; buffer_clear(&kex->peer); /* buffer_clear(&kex->my); */ kex->flags &= ~KEX_INIT_SENT; free(kex->name); kex->name = NULL; } void kex_send_kexinit(Kex *kex) { u_int32_t rnd = 0; u_char *cookie; u_int i; if (kex == NULL) { error("kex_send_kexinit: no kex, cannot rekey"); return; } if (kex->flags & KEX_INIT_SENT) { debug("KEX_INIT_SENT"); return; } kex->done = 0; /* generate a random cookie */ if (buffer_len(&kex->my) < KEX_COOKIE_LEN) fatal("kex_send_kexinit: kex proposal too short"); cookie = buffer_ptr(&kex->my); for (i = 0; i < KEX_COOKIE_LEN; i++) { if (i % 4 == 0) rnd = arc4random(); cookie[i] = rnd; rnd >>= 8; } packet_start(SSH2_MSG_KEXINIT); packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); packet_send(); debug("SSH2_MSG_KEXINIT sent"); kex->flags |= KEX_INIT_SENT; } /* ARGSUSED */ void kex_input_kexinit(int type, u_int32_t seq, void *ctxt) { char *ptr; u_int i, dlen; Kex *kex = (Kex *)ctxt; debug("SSH2_MSG_KEXINIT received"); if (kex == NULL) fatal("kex_input_kexinit: no kex, cannot rekey"); ptr = packet_get_raw(&dlen); buffer_append(&kex->peer, ptr, dlen); /* discard packet */ for (i = 0; i < KEX_COOKIE_LEN; i++) packet_get_char(); for (i = 0; i < PROPOSAL_MAX; i++) free(packet_get_string(NULL)); /* * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported * KEX method has the server move first, but a server might be using * a custom method or one that we otherwise don't support. We should * be prepared to remember first_kex_follows here so we can eat a * packet later. * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means * for cases where the server *doesn't* go first. I guess we should * ignore it when it is set for these cases, which is what we do now. */ (void) packet_get_char(); /* first_kex_follows */ (void) packet_get_int(); /* reserved */ packet_check_eom(); kex_kexinit_finish(kex); } Kex * kex_setup(char *proposal[PROPOSAL_MAX]) { Kex *kex; kex = xcalloc(1, sizeof(*kex)); buffer_init(&kex->peer); buffer_init(&kex->my); kex_prop2buf(&kex->my, proposal); kex->done = 0; kex_send_kexinit(kex); /* we start */ kex_reset_dispatch(); return kex; } static void kex_kexinit_finish(Kex *kex) { if (!(kex->flags & KEX_INIT_SENT)) kex_send_kexinit(kex); kex_choose_conf(kex); if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL) { (kex->kex[kex->kex_type])(kex); } else { fatal("Unsupported key exchange %d", kex->kex_type); } } static void choose_enc(Enc *enc, char *client, char *server) { char *name = match_list(client, server, NULL); if (name == NULL) fatal("no matching cipher found: client %s server %s", client, server); if ((enc->cipher = cipher_by_name(name)) == NULL) fatal("matching cipher is not supported: %s", name); enc->name = name; enc->enabled = 0; enc->iv = NULL; enc->iv_len = cipher_ivlen(enc->cipher); enc->key = NULL; enc->key_len = cipher_keylen(enc->cipher); enc->block_size = cipher_blocksize(enc->cipher); } static void choose_mac(Mac *mac, char *client, char *server) { char *name = match_list(client, server, NULL); if (name == NULL) fatal("no matching mac found: client %s server %s", client, server); if (mac_setup(mac, name) < 0) fatal("unsupported mac %s", name); /* truncate the key */ if (datafellows & SSH_BUG_HMAC) mac->key_len = 16; mac->name = name; mac->key = NULL; mac->enabled = 0; } static void choose_comp(Comp *comp, char *client, char *server) { char *name = match_list(client, server, NULL); if (name == NULL) fatal("no matching comp found: client %s server %s", client, server); if (strcmp(name, "zlib@openssh.com") == 0) { comp->type = COMP_DELAYED; } else if (strcmp(name, "zlib") == 0) { comp->type = COMP_ZLIB; } else if (strcmp(name, "none") == 0) { comp->type = COMP_NONE; } else { fatal("unsupported comp %s", name); } comp->name = name; } static void choose_kex(Kex *k, char *client, char *server) { const struct kexalg *kexalg; k->name = match_list(client, server, NULL); if (k->name == NULL) fatal("Unable to negotiate a key exchange method"); if ((kexalg = kex_alg_by_name(k->name)) == NULL) fatal("unsupported kex alg %s", k->name); k->kex_type = kexalg->type; k->hash_alg = kexalg->hash_alg; k->ec_nid = kexalg->ec_nid; } static void choose_hostkeyalg(Kex *k, char *client, char *server) { char *hostkeyalg = match_list(client, server, NULL); if (hostkeyalg == NULL) fatal("no hostkey alg"); k->hostkey_type = key_type_from_name(hostkeyalg); if (k->hostkey_type == KEY_UNSPEC) fatal("bad hostkey alg '%s'", hostkeyalg); free(hostkeyalg); } static int proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) { static int check[] = { PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 }; int *idx; char *p; for (idx = &check[0]; *idx != -1; idx++) { if ((p = strchr(my[*idx], ',')) != NULL) *p = '\0'; if ((p = strchr(peer[*idx], ',')) != NULL) *p = '\0'; if (strcmp(my[*idx], peer[*idx]) != 0) { debug2("proposal mismatch: my %s peer %s", my[*idx], peer[*idx]); return (0); } } debug2("proposals match"); return (1); } static void kex_choose_conf(Kex *kex) { Newkeys *newkeys; char **my, **peer; char **cprop, **sprop; int nenc, nmac, ncomp; u_int mode, ctos, need, dh_need, authlen; int first_kex_follows, type; #ifdef NONE_CIPHER_ENABLED int auth_flag; #endif my = kex_buf2prop(&kex->my, NULL); peer = kex_buf2prop(&kex->peer, &first_kex_follows); if (kex->server) { cprop=peer; sprop=my; } else { cprop=my; sprop=peer; } /* Check whether server offers roaming */ if (!kex->server) { char *roaming; roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); if (roaming) { kex->roaming = 1; free(roaming); } } /* Algorithm Negotiation */ #ifdef NONE_CIPHER_ENABLED auth_flag = packet_get_authentication_state(); debug ("AUTH STATE is %d", auth_flag); #endif for (mode = 0; mode < MODE_MAX; mode++) { newkeys = xcalloc(1, sizeof(*newkeys)); kex->newkeys[mode] = newkeys; ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc]); /* ignore mac for authenticated encryption */ authlen = cipher_authlen(newkeys->enc.cipher); if (authlen == 0) choose_mac(&newkeys->mac, cprop[nmac], sprop[nmac]); choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); #ifdef NONE_CIPHER_ENABLED debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name); if (strcmp(newkeys->enc.name, "none") == 0) { debug("Requesting NONE. Authflag is %d", auth_flag); if (auth_flag == 1) debug("None requested post authentication."); else fatal("Pre-authentication none cipher requests " "are not allowed."); } #endif debug("kex: %s %s %s %s", ctos ? "client->server" : "server->client", newkeys->enc.name, authlen == 0 ? newkeys->mac.name : "", newkeys->comp.name); } choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); need = dh_need = 0; for (mode = 0; mode < MODE_MAX; mode++) { newkeys = kex->newkeys[mode]; need = MAX(need, newkeys->enc.key_len); need = MAX(need, newkeys->enc.block_size); need = MAX(need, newkeys->enc.iv_len); need = MAX(need, newkeys->mac.key_len); dh_need = MAX(dh_need, cipher_seclen(newkeys->enc.cipher)); dh_need = MAX(dh_need, newkeys->enc.block_size); dh_need = MAX(dh_need, newkeys->enc.iv_len); dh_need = MAX(dh_need, newkeys->mac.key_len); } /* XXX need runden? */ kex->we_need = need; kex->dh_need = dh_need; /* ignore the next message if the proposals do not match */ if (first_kex_follows && !proposals_match(my, peer) && !(datafellows & SSH_BUG_FIRSTKEX)) { type = packet_read(); debug2("skipping next packet (type %u)", type); } kex_prop_free(my); kex_prop_free(peer); } static u_char * derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, const u_char *shared_secret, u_int slen) { Buffer b; struct ssh_digest_ctx *hashctx; char c = id; u_int have; size_t mdsz; u_char *digest; if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0) fatal("bad kex md size %zu", mdsz); digest = xmalloc(roundup(need, mdsz)); buffer_init(&b); buffer_append(&b, shared_secret, slen); /* K1 = HASH(K || H || "A" || session_id) */ if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL) fatal("%s: ssh_digest_start failed", __func__); if (ssh_digest_update_buffer(hashctx, &b) != 0 || ssh_digest_update(hashctx, hash, hashlen) != 0 || ssh_digest_update(hashctx, &c, 1) != 0 || ssh_digest_update(hashctx, kex->session_id, kex->session_id_len) != 0) fatal("%s: ssh_digest_update failed", __func__); if (ssh_digest_final(hashctx, digest, mdsz) != 0) fatal("%s: ssh_digest_final failed", __func__); ssh_digest_free(hashctx); /* * expand key: * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) * Key = K1 || K2 || ... || Kn */ for (have = mdsz; need > have; have += mdsz) { if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL) fatal("%s: ssh_digest_start failed", __func__); if (ssh_digest_update_buffer(hashctx, &b) != 0 || ssh_digest_update(hashctx, hash, hashlen) != 0 || ssh_digest_update(hashctx, digest, have) != 0) fatal("%s: ssh_digest_update failed", __func__); if (ssh_digest_final(hashctx, digest + have, mdsz) != 0) fatal("%s: ssh_digest_final failed", __func__); ssh_digest_free(hashctx); } buffer_free(&b); #ifdef DEBUG_KEX fprintf(stderr, "key '%c'== ", c); dump_digest("key", digest, need); #endif return digest; } Newkeys *current_keys[MODE_MAX]; #define NKEYS 6 void kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, const u_char *shared_secret, u_int slen) { u_char *keys[NKEYS]; u_int i, mode, ctos; for (i = 0; i < NKEYS; i++) { keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, shared_secret, slen); } debug2("kex_derive_keys"); for (mode = 0; mode < MODE_MAX; mode++) { current_keys[mode] = kex->newkeys[mode]; kex->newkeys[mode] = NULL; ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; } } void kex_derive_keys_bn(Kex *kex, u_char *hash, u_int hashlen, const BIGNUM *secret) { Buffer shared_secret; buffer_init(&shared_secret); buffer_put_bignum2(&shared_secret, secret); kex_derive_keys(kex, hash, hashlen, buffer_ptr(&shared_secret), buffer_len(&shared_secret)); buffer_free(&shared_secret); } Newkeys * kex_get_newkeys(int mode) { Newkeys *ret; ret = current_keys[mode]; current_keys[mode] = NULL; return ret; } void derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, u_int8_t cookie[8], u_int8_t id[16]) { u_int8_t nbuf[2048], obuf[SSH_DIGEST_MAX_LENGTH]; int len; struct ssh_digest_ctx *hashctx; if ((hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL) fatal("%s: ssh_digest_start", __func__); len = BN_num_bytes(host_modulus); if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) fatal("%s: bad host modulus (len %d)", __func__, len); BN_bn2bin(host_modulus, nbuf); if (ssh_digest_update(hashctx, nbuf, len) != 0) fatal("%s: ssh_digest_update failed", __func__); len = BN_num_bytes(server_modulus); if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) fatal("%s: bad server modulus (len %d)", __func__, len); BN_bn2bin(server_modulus, nbuf); if (ssh_digest_update(hashctx, nbuf, len) != 0 || ssh_digest_update(hashctx, cookie, 8) != 0) fatal("%s: ssh_digest_update failed", __func__); if (ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0) fatal("%s: ssh_digest_final failed", __func__); memcpy(id, obuf, ssh_digest_bytes(SSH_DIGEST_MD5)); explicit_bzero(nbuf, sizeof(nbuf)); explicit_bzero(obuf, sizeof(obuf)); } #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH) void dump_digest(char *msg, u_char *digest, int len) { int i; fprintf(stderr, "%s\n", msg); for (i = 0; i < len; i++) { fprintf(stderr, "%02x", digest[i]); if (i%32 == 31) fprintf(stderr, "\n"); else if (i%8 == 7) fprintf(stderr, " "); } fprintf(stderr, "\n"); } #endif