diff options
Diffstat (limited to 'kexc25519.c')
| -rw-r--r-- | kexc25519.c | 199 |
1 files changed, 199 insertions, 0 deletions
diff --git a/kexc25519.c b/kexc25519.c new file mode 100644 index 0000000..f13d766 --- /dev/null +++ b/kexc25519.c @@ -0,0 +1,199 @@ +/* $OpenBSD: kexc25519.c,v 1.17 2019/01/21 10:40:11 djm Exp $ */ +/* + * Copyright (c) 2019 Markus Friedl. All rights reserved. + * Copyright (c) 2010 Damien Miller. All rights reserved. + * Copyright (c) 2013 Aris Adamantiadis. 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 <stdio.h> +#include <string.h> +#include <signal.h> + +#include "sshkey.h" +#include "kex.h" +#include "sshbuf.h" +#include "digest.h" +#include "ssherr.h" +#include "ssh2.h" + +extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE], + const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE]) + __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE))) + __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE))) + __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE))); + +void +kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE]) +{ + static const u_char basepoint[CURVE25519_SIZE] = {9}; + + arc4random_buf(key, CURVE25519_SIZE); + crypto_scalarmult_curve25519(pub, key, basepoint); +} + +int +kexc25519_shared_key_ext(const u_char key[CURVE25519_SIZE], + const u_char pub[CURVE25519_SIZE], struct sshbuf *out, int raw) +{ + u_char shared_key[CURVE25519_SIZE]; + u_char zero[CURVE25519_SIZE]; + int r; + + crypto_scalarmult_curve25519(shared_key, key, pub); + + /* Check for all-zero shared secret */ + explicit_bzero(zero, CURVE25519_SIZE); + if (timingsafe_bcmp(zero, shared_key, CURVE25519_SIZE) == 0) + return SSH_ERR_KEY_INVALID_EC_VALUE; + +#ifdef DEBUG_KEXECDH + dump_digest("shared secret", shared_key, CURVE25519_SIZE); +#endif + if (raw) + r = sshbuf_put(out, shared_key, CURVE25519_SIZE); + else + r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE); + explicit_bzero(shared_key, CURVE25519_SIZE); + return r; +} + +int +kexc25519_shared_key(const u_char key[CURVE25519_SIZE], + const u_char pub[CURVE25519_SIZE], struct sshbuf *out) +{ + return kexc25519_shared_key_ext(key, pub, out, 0); +} + +int +kex_c25519_keypair(struct kex *kex) +{ + struct sshbuf *buf = NULL; + u_char *cp = NULL; + int r; + + if ((buf = sshbuf_new()) == NULL) + return SSH_ERR_ALLOC_FAIL; + if ((r = sshbuf_reserve(buf, CURVE25519_SIZE, &cp)) != 0) + goto out; + kexc25519_keygen(kex->c25519_client_key, cp); +#ifdef DEBUG_KEXECDH + dump_digest("client public key c25519:", cp, CURVE25519_SIZE); +#endif + kex->client_pub = buf; + buf = NULL; + out: + sshbuf_free(buf); + return r; +} + +int +kex_c25519_enc(struct kex *kex, const struct sshbuf *client_blob, + struct sshbuf **server_blobp, struct sshbuf **shared_secretp) +{ + struct sshbuf *server_blob = NULL; + struct sshbuf *buf = NULL; + const u_char *client_pub; + u_char *server_pub; + u_char server_key[CURVE25519_SIZE]; + int r; + + *server_blobp = NULL; + *shared_secretp = NULL; + + if (sshbuf_len(client_blob) != CURVE25519_SIZE) { + r = SSH_ERR_SIGNATURE_INVALID; + goto out; + } + client_pub = sshbuf_ptr(client_blob); +#ifdef DEBUG_KEXECDH + dump_digest("client public key 25519:", client_pub, CURVE25519_SIZE); +#endif + /* allocate space for encrypted KEM key and ECDH pub key */ + if ((server_blob = sshbuf_new()) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + if ((r = sshbuf_reserve(server_blob, CURVE25519_SIZE, &server_pub)) != 0) + goto out; + kexc25519_keygen(server_key, server_pub); + /* allocate shared secret */ + if ((buf = sshbuf_new()) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 0)) < 0) + goto out; +#ifdef DEBUG_KEXECDH + dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE); + dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf)); +#endif + *server_blobp = server_blob; + *shared_secretp = buf; + server_blob = NULL; + buf = NULL; + out: + explicit_bzero(server_key, sizeof(server_key)); + sshbuf_free(server_blob); + sshbuf_free(buf); + return r; +} + +int +kex_c25519_dec(struct kex *kex, const struct sshbuf *server_blob, + struct sshbuf **shared_secretp) +{ + struct sshbuf *buf = NULL; + const u_char *server_pub; + int r; + + *shared_secretp = NULL; + + if (sshbuf_len(server_blob) != CURVE25519_SIZE) { + r = SSH_ERR_SIGNATURE_INVALID; + goto out; + } + server_pub = sshbuf_ptr(server_blob); +#ifdef DEBUG_KEXECDH + dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE); +#endif + /* shared secret */ + if ((buf = sshbuf_new()) == NULL) { + r = SSH_ERR_ALLOC_FAIL; + goto out; + } + if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub, + buf, 0)) < 0) + goto out; +#ifdef DEBUG_KEXECDH + dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf)); +#endif + *shared_secretp = buf; + buf = NULL; + out: + sshbuf_free(buf); + return r; +} |