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Diffstat (limited to '')
| -rw-r--r-- | kexgen.c | 371 |
1 files changed, 371 insertions, 0 deletions
diff --git a/kexgen.c b/kexgen.c new file mode 100644 index 0000000..20f3c57 --- /dev/null +++ b/kexgen.c @@ -0,0 +1,371 @@ +/* $OpenBSD: kexgen.c,v 1.8 2021/12/19 22:08:06 djm Exp $ */ +/* + * Copyright (c) 2019 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 <sys/types.h> + +#include <stdarg.h> +#include <stdio.h> +#include <string.h> +#include <signal.h> + +#include "sshkey.h" +#include "kex.h" +#include "log.h" +#include "packet.h" +#include "ssh2.h" +#include "sshbuf.h" +#include "digest.h" +#include "ssherr.h" + +static int input_kex_gen_init(int, u_int32_t, struct ssh *); +static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh); + +static int +kex_gen_hash( + int hash_alg, + const struct sshbuf *client_version, + const struct sshbuf *server_version, + const struct sshbuf *client_kexinit, + const struct sshbuf *server_kexinit, + const struct sshbuf *server_host_key_blob, + const struct sshbuf *client_pub, + const struct sshbuf *server_pub, + const struct sshbuf *shared_secret, + u_char *hash, size_t *hashlen) +{ + struct sshbuf *b; + int r; + + if (*hashlen < ssh_digest_bytes(hash_alg)) + return SSH_ERR_INVALID_ARGUMENT; + if ((b = sshbuf_new()) == NULL) + return SSH_ERR_ALLOC_FAIL; + if ((r = sshbuf_put_stringb(b, client_version)) != 0 || + (r = sshbuf_put_stringb(b, server_version)) != 0 || + /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ + (r = sshbuf_put_u32(b, sshbuf_len(client_kexinit) + 1)) != 0 || + (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 || + (r = sshbuf_putb(b, client_kexinit)) != 0 || + (r = sshbuf_put_u32(b, sshbuf_len(server_kexinit) + 1)) != 0 || + (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 || + (r = sshbuf_putb(b, server_kexinit)) != 0 || + (r = sshbuf_put_stringb(b, server_host_key_blob)) != 0 || + (r = sshbuf_put_stringb(b, client_pub)) != 0 || + (r = sshbuf_put_stringb(b, server_pub)) != 0 || + (r = sshbuf_putb(b, shared_secret)) != 0) { + sshbuf_free(b); + return r; + } +#ifdef DEBUG_KEX + sshbuf_dump(b, stderr); +#endif + if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) { + sshbuf_free(b); + return SSH_ERR_LIBCRYPTO_ERROR; + } + sshbuf_free(b); + *hashlen = ssh_digest_bytes(hash_alg); +#ifdef DEBUG_KEX + dump_digest("hash", hash, *hashlen); +#endif + return 0; +} + +int +kex_gen_client(struct ssh *ssh) +{ + struct kex *kex = ssh->kex; + int r; + + switch (kex->kex_type) { +#ifdef WITH_OPENSSL + case KEX_DH_GRP1_SHA1: + case KEX_DH_GRP14_SHA1: + case KEX_DH_GRP14_SHA256: + case KEX_DH_GRP16_SHA512: + case KEX_DH_GRP18_SHA512: + r = kex_dh_keypair(kex); + break; + case KEX_ECDH_SHA2: + r = kex_ecdh_keypair(kex); + break; +#endif + case KEX_C25519_SHA256: + r = kex_c25519_keypair(kex); + break; + case KEX_KEM_SNTRUP761X25519_SHA512: + r = kex_kem_sntrup761x25519_keypair(kex); + break; + default: + r = SSH_ERR_INVALID_ARGUMENT; + break; + } + if (r != 0) + return r; + if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 || + (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 || + (r = sshpkt_send(ssh)) != 0) + return r; + debug("expecting SSH2_MSG_KEX_ECDH_REPLY"); + ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply); + return 0; +} + +static int +input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh) +{ + struct kex *kex = ssh->kex; + struct sshkey *server_host_key = NULL; + struct sshbuf *shared_secret = NULL; + struct sshbuf *server_blob = NULL; + struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; + u_char *signature = NULL; + u_char hash[SSH_DIGEST_MAX_LENGTH]; + size_t slen, hashlen; + int r; + + debug("SSH2_MSG_KEX_ECDH_REPLY received"); + ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error); + + /* hostkey */ + if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) + goto out; + /* sshkey_fromb() consumes its buffer, so make a copy */ + if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + if ((r = sshkey_fromb(tmp, &server_host_key)) != 0) + goto out; + if ((r = kex_verify_host_key(ssh, server_host_key)) != 0) + goto out; + + /* Q_S, server public key */ + /* signed H */ + if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 || + (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || + (r = sshpkt_get_end(ssh)) != 0) + goto out; + + /* compute shared secret */ + switch (kex->kex_type) { +#ifdef WITH_OPENSSL + case KEX_DH_GRP1_SHA1: + case KEX_DH_GRP14_SHA1: + case KEX_DH_GRP14_SHA256: + case KEX_DH_GRP16_SHA512: + case KEX_DH_GRP18_SHA512: + r = kex_dh_dec(kex, server_blob, &shared_secret); + break; + case KEX_ECDH_SHA2: + r = kex_ecdh_dec(kex, server_blob, &shared_secret); + break; +#endif + case KEX_C25519_SHA256: + r = kex_c25519_dec(kex, server_blob, &shared_secret); + break; + case KEX_KEM_SNTRUP761X25519_SHA512: + r = kex_kem_sntrup761x25519_dec(kex, server_blob, + &shared_secret); + break; + default: + r = SSH_ERR_INVALID_ARGUMENT; + break; + } + if (r !=0 ) + goto out; + + /* calc and verify H */ + hashlen = sizeof(hash); + if ((r = kex_gen_hash( + kex->hash_alg, + kex->client_version, + kex->server_version, + kex->my, + kex->peer, + server_host_key_blob, + kex->client_pub, + server_blob, + shared_secret, + hash, &hashlen)) != 0) + goto out; + + if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen, + kex->hostkey_alg, ssh->compat, NULL)) != 0) + goto out; + + if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || + (r = kex_send_newkeys(ssh)) != 0) + goto out; + + /* save initial signature and hostkey */ + if ((kex->flags & KEX_INITIAL) != 0) { + if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) { + r = SSH_ERR_INTERNAL_ERROR; + goto out; + } + if ((kex->initial_sig = sshbuf_new()) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0) + goto out; + kex->initial_hostkey = server_host_key; + server_host_key = NULL; + } + /* success */ +out: + explicit_bzero(hash, sizeof(hash)); + explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); + explicit_bzero(kex->sntrup761_client_key, + sizeof(kex->sntrup761_client_key)); + sshbuf_free(server_host_key_blob); + free(signature); + sshbuf_free(tmp); + sshkey_free(server_host_key); + sshbuf_free(server_blob); + sshbuf_free(shared_secret); + sshbuf_free(kex->client_pub); + kex->client_pub = NULL; + return r; +} + +int +kex_gen_server(struct ssh *ssh) +{ + debug("expecting SSH2_MSG_KEX_ECDH_INIT"); + ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); + return 0; +} + +static int +input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) +{ + struct kex *kex = ssh->kex; + struct sshkey *server_host_private, *server_host_public; + struct sshbuf *shared_secret = NULL; + struct sshbuf *server_pubkey = NULL; + struct sshbuf *client_pubkey = NULL; + struct sshbuf *server_host_key_blob = NULL; + u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; + size_t slen, hashlen; + int r; + + debug("SSH2_MSG_KEX_ECDH_INIT received"); + ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error); + + if ((r = kex_load_hostkey(ssh, &server_host_private, + &server_host_public)) != 0) + goto out; + + if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || + (r = sshpkt_get_end(ssh)) != 0) + goto out; + + /* compute shared secret */ + switch (kex->kex_type) { +#ifdef WITH_OPENSSL + case KEX_DH_GRP1_SHA1: + case KEX_DH_GRP14_SHA1: + case KEX_DH_GRP14_SHA256: + case KEX_DH_GRP16_SHA512: + case KEX_DH_GRP18_SHA512: + r = kex_dh_enc(kex, client_pubkey, &server_pubkey, + &shared_secret); + break; + case KEX_ECDH_SHA2: + r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, + &shared_secret); + break; +#endif + case KEX_C25519_SHA256: + r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, + &shared_secret); + break; + case KEX_KEM_SNTRUP761X25519_SHA512: + r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, + &server_pubkey, &shared_secret); + break; + default: + r = SSH_ERR_INVALID_ARGUMENT; + break; + } + if (r !=0 ) + goto out; + + /* calc H */ + 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; + hashlen = sizeof(hash); + if ((r = kex_gen_hash( + kex->hash_alg, + kex->client_version, + kex->server_version, + kex->peer, + kex->my, + server_host_key_blob, + client_pubkey, + server_pubkey, + 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, ECDH pubkey 'Q_S' and signed H */ + if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || + (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || + (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || + (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)); + sshbuf_free(server_host_key_blob); + free(signature); + sshbuf_free(shared_secret); + sshbuf_free(client_pubkey); + sshbuf_free(server_pubkey); + return r; +} |