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- /* $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;
- }
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