/* $NetBSD: kexgen.c,v 1.2.4.1 2023/12/25 12:31:04 martin Exp $ */ /* $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" __RCSID("$NetBSD"); #include #include #include #include #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 /* WITH_OPENSSL */ 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 /* WITH_OPENSSL */ 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 /* WITH_OPENSSL */ 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; }