/* * 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("$OpenBSD: kexdh.c,v 1.17 2002/02/28 15:46:33 markus Exp $"); #include #include #include "xmalloc.h" #include "buffer.h" #include "bufaux.h" #include "key.h" #include "kex.h" #include "log.h" #include "packet.h" #include "dh.h" #include "ssh2.h" #include "monitor.h" #include "monitor_wrap.h" /* Imports */ extern int use_privsep; extern int mm_recvfd; static u_char * kex_dh_hash( char *client_version_string, char *server_version_string, char *ckexinit, int ckexinitlen, char *skexinit, int skexinitlen, u_char *serverhostkeyblob, int sbloblen, BIGNUM *client_dh_pub, BIGNUM *server_dh_pub, BIGNUM *shared_secret) { Buffer b; static u_char digest[EVP_MAX_MD_SIZE]; const EVP_MD *evp_md = EVP_sha1(); EVP_MD_CTX md; buffer_init(&b); buffer_put_cstring(&b, client_version_string); buffer_put_cstring(&b, server_version_string); /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ buffer_put_int(&b, ckexinitlen+1); buffer_put_char(&b, SSH2_MSG_KEXINIT); buffer_append(&b, ckexinit, ckexinitlen); buffer_put_int(&b, skexinitlen+1); buffer_put_char(&b, SSH2_MSG_KEXINIT); buffer_append(&b, skexinit, skexinitlen); buffer_put_string(&b, serverhostkeyblob, sbloblen); buffer_put_bignum2(&b, client_dh_pub); buffer_put_bignum2(&b, server_dh_pub); buffer_put_bignum2(&b, shared_secret); #ifdef DEBUG_KEX buffer_dump(&b); #endif EVP_DigestInit(&md, evp_md); EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); EVP_DigestFinal(&md, digest, NULL); buffer_free(&b); #ifdef DEBUG_KEX dump_digest("hash", digest, EVP_MD_size(evp_md)); #endif return digest; } /* client */ static void kexdh_client(Kex *kex) { BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; DH *dh; Key *server_host_key; u_char *server_host_key_blob = NULL, *signature = NULL; u_char *kbuf, *hash; u_int klen, kout, slen, sbloblen; /* generate and send 'e', client DH public key */ dh = dh_new_group1(); dh_gen_key(dh, kex->we_need * 8); packet_start(SSH2_MSG_KEXDH_INIT); packet_put_bignum2(dh->pub_key); packet_send(); debug("sending SSH2_MSG_KEXDH_INIT"); #ifdef DEBUG_KEXDH DHparams_print_fp(stderr, dh); fprintf(stderr, "pub= "); BN_print_fp(stderr, dh->pub_key); fprintf(stderr, "\n"); #endif debug("expecting SSH2_MSG_KEXDH_REPLY"); packet_read_expect(SSH2_MSG_KEXDH_REPLY); /* key, cert */ server_host_key_blob = packet_get_string(&sbloblen); server_host_key = key_from_blob(server_host_key_blob, sbloblen); if (server_host_key == NULL) fatal("cannot decode server_host_key_blob"); if (server_host_key->type != kex->hostkey_type) fatal("type mismatch for decoded server_host_key_blob"); if (kex->verify_host_key == NULL) fatal("cannot verify server_host_key"); if (kex->verify_host_key(server_host_key) == -1) fatal("server_host_key verification failed"); /* DH paramter f, server public DH key */ if ((dh_server_pub = BN_new()) == NULL) fatal("dh_server_pub == NULL"); packet_get_bignum2(dh_server_pub); #ifdef DEBUG_KEXDH fprintf(stderr, "dh_server_pub= "); BN_print_fp(stderr, dh_server_pub); fprintf(stderr, "\n"); debug("bits %d", BN_num_bits(dh_server_pub)); #endif /* signed H */ signature = packet_get_string(&slen); packet_check_eom(); if (!dh_pub_is_valid(dh, dh_server_pub)) packet_disconnect("bad server public DH value"); klen = DH_size(dh); kbuf = xmalloc(klen); kout = DH_compute_key(kbuf, dh_server_pub, dh); #ifdef DEBUG_KEXDH dump_digest("shared secret", kbuf, kout); #endif if ((shared_secret = BN_new()) == NULL) fatal("kexdh_client: BN_new failed"); BN_bin2bn(kbuf, kout, shared_secret); memset(kbuf, 0, klen); xfree(kbuf); /* calc and verify H */ hash = kex_dh_hash( kex->client_version_string, kex->server_version_string, buffer_ptr(&kex->my), buffer_len(&kex->my), buffer_ptr(&kex->peer), buffer_len(&kex->peer), server_host_key_blob, sbloblen, dh->pub_key, dh_server_pub, shared_secret ); xfree(server_host_key_blob); BN_clear_free(dh_server_pub); DH_free(dh); if (key_verify(server_host_key, signature, slen, hash, 20) != 1) fatal("key_verify failed for server_host_key"); key_free(server_host_key); xfree(signature); /* save session id */ if (kex->session_id == NULL) { kex->session_id_len = 20; kex->session_id = xmalloc(kex->session_id_len); memcpy(kex->session_id, hash, kex->session_id_len); } kex_derive_keys(kex, hash, shared_secret); BN_clear_free(shared_secret); kex_finish(kex); } /* server */ static void kexdh_server(Kex *kex) { BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; DH *dh; Key *server_host_key; u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; u_int sbloblen, klen, kout; u_int slen; /* generate server DH public key */ dh = dh_new_group1(); dh_gen_key(dh, kex->we_need * 8); debug("expecting SSH2_MSG_KEXDH_INIT"); packet_read_expect(SSH2_MSG_KEXDH_INIT); if (kex->load_host_key == NULL) fatal("Cannot load hostkey"); server_host_key = kex->load_host_key(kex->hostkey_type); if (server_host_key == NULL) fatal("Unsupported hostkey type %d", kex->hostkey_type); /* key, cert */ if ((dh_client_pub = BN_new()) == NULL) fatal("dh_client_pub == NULL"); packet_get_bignum2(dh_client_pub); packet_check_eom(); #ifdef DEBUG_KEXDH fprintf(stderr, "dh_client_pub= "); BN_print_fp(stderr, dh_client_pub); fprintf(stderr, "\n"); debug("bits %d", BN_num_bits(dh_client_pub)); #endif #ifdef DEBUG_KEXDH DHparams_print_fp(stderr, dh); fprintf(stderr, "pub= "); BN_print_fp(stderr, dh->pub_key); fprintf(stderr, "\n"); #endif if (!dh_pub_is_valid(dh, dh_client_pub)) packet_disconnect("bad client public DH value"); klen = DH_size(dh); kbuf = xmalloc(klen); kout = DH_compute_key(kbuf, dh_client_pub, dh); #ifdef DEBUG_KEXDH dump_digest("shared secret", kbuf, kout); #endif if ((shared_secret = BN_new()) == NULL) fatal("kexdh_server: BN_new failed"); BN_bin2bn(kbuf, kout, shared_secret); memset(kbuf, 0, klen); xfree(kbuf); key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); /* calc H */ hash = kex_dh_hash( kex->client_version_string, kex->server_version_string, buffer_ptr(&kex->peer), buffer_len(&kex->peer), buffer_ptr(&kex->my), buffer_len(&kex->my), server_host_key_blob, sbloblen, dh_client_pub, dh->pub_key, shared_secret ); BN_clear_free(dh_client_pub); /* save session id := H */ /* XXX hashlen depends on KEX */ if (kex->session_id == NULL) { kex->session_id_len = 20; kex->session_id = xmalloc(kex->session_id_len); memcpy(kex->session_id, hash, kex->session_id_len); } /* sign H */ /* XXX hashlen depends on KEX */ if (use_privsep) mm_key_sign(mm_recvfd, kex->host_key_index(server_host_key), &signature, &slen, hash, 20); else key_sign(server_host_key, &signature, &slen, hash, 20); /* destroy_sensitive_data(); */ /* send server hostkey, DH pubkey 'f' and singed H */ packet_start(SSH2_MSG_KEXDH_REPLY); packet_put_string(server_host_key_blob, sbloblen); packet_put_bignum2(dh->pub_key); /* f */ packet_put_string(signature, slen); packet_send(); xfree(signature); xfree(server_host_key_blob); /* have keys, free DH */ DH_free(dh); kex_derive_keys(kex, hash, shared_secret); BN_clear_free(shared_secret); kex_finish(kex); } void kexdh(Kex *kex) { if (kex->server) kexdh_server(kex); else kexdh_client(kex); }