- djm@cvs.openbsd.org 2013/11/21 00:45:44
[Makefile.in PROTOCOL PROTOCOL.chacha20poly1305 authfile.c chacha.c]
[chacha.h cipher-chachapoly.c cipher-chachapoly.h cipher.c cipher.h]
[dh.c myproposal.h packet.c poly1305.c poly1305.h servconf.c ssh.1]
[ssh.c ssh_config.5 sshd_config.5] Add a new protocol 2 transport
cipher "chacha20-poly1305@openssh.com" that combines Daniel
Bernstein's ChaCha20 stream cipher and Poly1305 MAC to build an
authenticated encryption mode.
Inspired by and similar to Adam Langley's proposal for TLS:
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
but differs in layout used for the MAC calculation and the use of a
second ChaCha20 instance to separately encrypt packet lengths.
Details are in the PROTOCOL.chacha20poly1305 file.
Feedback markus@, naddy@; manpage bits Loganden Velvindron @ AfriNIC
ok markus@ naddy@
diff --git a/cipher-chachapoly.c b/cipher-chachapoly.c
new file mode 100644
index 0000000..20628ab
--- /dev/null
+++ b/cipher-chachapoly.c
@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* $OpenBSD: cipher-chachapoly.c,v 1.2 2013/11/21 02:50:00 djm Exp $ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+#include <stdarg.h> /* needed for log.h */
+#include <string.h>
+#include <stdio.h> /* needed for misc.h */
+
+#include "log.h"
+#include "misc.h"
+#include "cipher-chachapoly.h"
+
+void chachapoly_init(struct chachapoly_ctx *ctx,
+ const u_char *key, u_int keylen)
+{
+ if (keylen != (32 + 32)) /* 2 x 256 bit keys */
+ fatal("%s: invalid keylen %u", __func__, keylen);
+ chacha_keysetup(&ctx->main_ctx, key, 256);
+ chacha_keysetup(&ctx->header_ctx, key + 32, 256);
+}
+
+/*
+ * chachapoly_crypt() operates as following:
+ * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
+ * Theses bytes are treated as additional authenticated data.
+ * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
+ * Use POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the
+ * authentication tag.
+ * This tag is written on encryption and verified on decryption.
+ * Both 'aadlen' and 'authlen' can be set to 0.
+ */
+int
+chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
+ const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
+{
+ u_char seqbuf[8];
+ u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB. little-endian */
+ u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
+ int r = -1;
+
+ /*
+ * Run ChaCha20 once to generate the Poly1305 key. The IV is the
+ * packet sequence number.
+ */
+ bzero(poly_key, sizeof(poly_key));
+ put_u64(seqbuf, seqnr);
+ chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
+ chacha_encrypt_bytes(&ctx->main_ctx,
+ poly_key, poly_key, sizeof(poly_key));
+ /* Set Chacha's block counter to 1 */
+ chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
+
+ /* If decrypting, check tag before anything else */
+ if (!do_encrypt) {
+ const u_char *tag = src + aadlen + len;
+
+ poly1305_auth(expected_tag, src, aadlen + len, poly_key);
+ if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0)
+ goto out;
+ }
+ /* Crypt additional data */
+ if (aadlen) {
+ chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
+ chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
+ }
+ chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
+ dest + aadlen, len);
+
+ /* If encrypting, calculate and append tag */
+ if (do_encrypt) {
+ poly1305_auth(dest + aadlen + len, dest, aadlen + len,
+ poly_key);
+ }
+ r = 0;
+
+ out:
+ bzero(expected_tag, sizeof(expected_tag));
+ bzero(seqbuf, sizeof(seqbuf));
+ bzero(poly_key, sizeof(poly_key));
+ return r;
+}
+
+int
+chachapoly_get_length(struct chachapoly_ctx *ctx,
+ u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
+{
+ u_char buf[4], seqbuf[8];
+
+ if (len < 4)
+ return -1; /* Insufficient length */
+ put_u64(seqbuf, seqnr);
+ chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
+ chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
+ *plenp = get_u32(buf);
+ return 0;
+}
+