external/openssh: update to 6.8p1.

In preparation for some updates to external/openssh to make it work with
BoringSSL, this change updates the code to a recent version. The current
version (5.9p1) is coming up on four years old now.

  * Confirmed that f5c67b478bef9992de9e9ec91ce10af4f6205e0d matches
    OpenSSH 5.9p1 exactly (save for the removal of the scard
    subdirectory).

  * Downloaded openssh-6.8p1.tar.gz (SHA256:
    3ff64ce73ee124480b5bf767b9830d7d3c03bbcb6abe716b78f0192c37ce160e)
    and verified with PGP signature. (I've verified Damien's key in
    person previously.)

  * Applied changes between f5c67b478bef9992de9e9ec91ce10af4f6205e0d and
    OpenSSH 5.9p1 to 6.8p1 and updated the build as best I can. The
    ugliest change is probably the duplication of umac.c to umac128.c
    because Android conditionally compiles that file twice. See the
    comment in those files.

Change-Id: I63cb07a8118afb5a377f116087a0882914cea486
diff --git a/kexc25519.c b/kexc25519.c
new file mode 100644
index 0000000..b6e6c40
--- /dev/null
+++ b/kexc25519.c
@@ -0,0 +1,128 @@
+/* $OpenBSD: kexc25519.c,v 1.8 2015/01/19 20:16:15 markus 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;
+
+	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 char *ckexinit, size_t ckexinitlen,
+    const 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;
+}