cipher-chachapoly.c revision 323134 
1/*
2 * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
3 *
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
7 *
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 */
16
17/* $OpenBSD: cipher-chachapoly.c,v 1.8 2016/08/03 05:41:57 djm Exp $ */
18
19#include "includes.h"
20
21#include <sys/types.h>
22#include <stdarg.h> /* needed for log.h */
23#include <string.h>
24#include <stdio.h>  /* needed for misc.h */
25
26#include "log.h"
27#include "sshbuf.h"
28#include "ssherr.h"
29#include "cipher-chachapoly.h"
30
31int
32chachapoly_init(struct chachapoly_ctx *ctx,
33    const u_char *key, u_int keylen)
34{
35	if (keylen != (32 + 32)) /* 2 x 256 bit keys */
36		return SSH_ERR_INVALID_ARGUMENT;
37	chacha_keysetup(&ctx->main_ctx, key, 256);
38	chacha_keysetup(&ctx->header_ctx, key + 32, 256);
39	return 0;
40}
41
42/*
43 * chachapoly_crypt() operates as following:
44 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
45 * to 'dest'. The ciphertext here is treated as additional authenticated
46 * data for MAC calculation.
47 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
48 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
49 * tag. This tag is written on encryption and verified on decryption.
50 */
51int
52chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
53    const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
54{
55	u_char seqbuf[8];
56	const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
57	u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
58	int r = SSH_ERR_INTERNAL_ERROR;
59
60	/*
61	 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
62	 * packet sequence number.
63	 */
64	memset(poly_key, 0, sizeof(poly_key));
65	POKE_U64(seqbuf, seqnr);
66	chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
67	chacha_encrypt_bytes(&ctx->main_ctx,
68	    poly_key, poly_key, sizeof(poly_key));
69
70	/* If decrypting, check tag before anything else */
71	if (!do_encrypt) {
72		const u_char *tag = src + aadlen + len;
73
74		poly1305_auth(expected_tag, src, aadlen + len, poly_key);
75		if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
76			r = SSH_ERR_MAC_INVALID;
77			goto out;
78		}
79	}
80
81	/* Crypt additional data */
82	if (aadlen) {
83		chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
84		chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
85	}
86
87	/* Set Chacha's block counter to 1 */
88	chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
89	chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
90	    dest + aadlen, len);
91
92	/* If encrypting, calculate and append tag */
93	if (do_encrypt) {
94		poly1305_auth(dest + aadlen + len, dest, aadlen + len,
95		    poly_key);
96	}
97	r = 0;
98 out:
99	explicit_bzero(expected_tag, sizeof(expected_tag));
100	explicit_bzero(seqbuf, sizeof(seqbuf));
101	explicit_bzero(poly_key, sizeof(poly_key));
102	return r;
103}
104
105/* Decrypt and extract the encrypted packet length */
106int
107chachapoly_get_length(struct chachapoly_ctx *ctx,
108    u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
109{
110	u_char buf[4], seqbuf[8];
111
112	if (len < 4)
113		return SSH_ERR_MESSAGE_INCOMPLETE;
114	POKE_U64(seqbuf, seqnr);
115	chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
116	chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
117	*plenp = PEEK_U32(buf);
118	return 0;
119}
120