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+/* $OpenBSD: kexc25519.c,v 1.10 2016/05/02 08:49:03 djm Exp $ */
+/*
+ * Copyright (c) 2001, 2013 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 <signal.h>
+#include <string.h>
+
+#include <openssl/bn.h>
+#include <openssl/evp.h>
+
+#include "sshbuf.h"
+#include "ssh2.h"
+#include "sshkey.h"
+#include "cipher.h"
+#include "kex.h"
+#include "log.h"
+#include "digest.h"
+#include "ssherr.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(const u_char key[CURVE25519_SIZE],
+ const u_char pub[CURVE25519_SIZE], struct sshbuf *out)
+{
+ u_char shared_key[CURVE25519_SIZE];
+ int r;
+
+ /* Check for all-zero public key */
+ explicit_bzero(shared_key, CURVE25519_SIZE);
+ if (timingsafe_bcmp(pub, shared_key, CURVE25519_SIZE) == 0)
+ return SSH_ERR_KEY_INVALID_EC_VALUE;
+
+ crypto_scalarmult_curve25519(shared_key, key, pub);
+#ifdef DEBUG_KEXECDH
+ dump_digest("shared secret", shared_key, CURVE25519_SIZE);
+#endif
+ sshbuf_reset(out);
+ r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE);
+ explicit_bzero(shared_key, CURVE25519_SIZE);
+ return r;
+}
+
+int
+kex_c25519_hash(
+ int hash_alg,
+ const char *client_version_string,
+ const char *server_version_string,
+ const u_char *ckexinit, size_t ckexinitlen,
+ const u_char *skexinit, size_t skexinitlen,
+ const u_char *serverhostkeyblob, size_t sbloblen,
+ const u_char client_dh_pub[CURVE25519_SIZE],
+ const u_char server_dh_pub[CURVE25519_SIZE],
+ const u_char *shared_secret, size_t secretlen,
+ 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_cstring(b, client_version_string)) < 0 ||
+ (r = sshbuf_put_cstring(b, server_version_string)) < 0 ||
+ /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
+ (r = sshbuf_put_u32(b, ckexinitlen+1)) < 0 ||
+ (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
+ (r = sshbuf_put(b, ckexinit, ckexinitlen)) < 0 ||
+ (r = sshbuf_put_u32(b, skexinitlen+1)) < 0 ||
+ (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
+ (r = sshbuf_put(b, skexinit, skexinitlen)) < 0 ||
+ (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) < 0 ||
+ (r = sshbuf_put_string(b, client_dh_pub, CURVE25519_SIZE)) < 0 ||
+ (r = sshbuf_put_string(b, server_dh_pub, CURVE25519_SIZE)) < 0 ||
+ (r = sshbuf_put(b, shared_secret, secretlen)) < 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;
+}