cipher-chachapoly.c revision 295367 
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 1.7 2015/01/14 10:24:42 markus 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 chachapoly_init(struct chachapoly_ctx *ctx,
32    const u_char *key, u_int keylen)
33{
34	if (keylen != (32 + 32)) /* 2 x 256 bit keys */
35		return SSH_ERR_INVALID_ARGUMENT;
36	chacha_keysetup(&ctx->main_ctx, key, 256);
37	chacha_keysetup(&ctx->header_ctx, key + 32, 256);
38	return 0;
39}
40
41/*
42 * chachapoly_crypt() operates as following:
43 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
44 * to 'dest'. The ciphertext here is treated as additional authenticated
45 * data for MAC calculation.
46 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
47 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
48 * tag. This tag is written on encryption and verified on decryption.
49 */
50int
51chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
52    const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
53{
54	u_char seqbuf[8];
55	const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
56	u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
57	int r = SSH_ERR_INTERNAL_ERROR;
58
59	/*
60	 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
61	 * packet sequence number.
62	 */
63	memset(poly_key, 0, sizeof(poly_key));
64	POKE_U64(seqbuf, seqnr);
65	chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
66	chacha_encrypt_bytes(&ctx->main_ctx,
67	    poly_key, poly_key, sizeof(poly_key));
68
69	/* If decrypting, check tag before anything else */
70	if (!do_encrypt) {
71		const u_char *tag = src + aadlen + len;
72
73		poly1305_auth(expected_tag, src, aadlen + len, poly_key);
74		if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
75			r = SSH_ERR_MAC_INVALID;
76			goto out;
77		}
78	}
79
80	/* Crypt additional data */
81	if (aadlen) {
82		chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
83		chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
84	}
85
86	/* Set Chacha's block counter to 1 */
87	chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
88	chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
89	    dest + aadlen, len);
90
91	/* If encrypting, calculate and append tag */
92	if (do_encrypt) {
93		poly1305_auth(dest + aadlen + len, dest, aadlen + len,
94		    poly_key);
95	}
96	r = 0;
97 out:
98	explicit_bzero(expected_tag, sizeof(expected_tag));
99	explicit_bzero(seqbuf, sizeof(seqbuf));
100	explicit_bzero(poly_key, sizeof(poly_key));
101	return r;
102}
103
104/* Decrypt and extract the encrypted packet length */
105int
106chachapoly_get_length(struct chachapoly_ctx *ctx,
107    u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
108{
109	u_char buf[4], seqbuf[8];
110
111	if (len < 4)
112		return SSH_ERR_MESSAGE_INCOMPLETE;
113	POKE_U64(seqbuf, seqnr);
114	chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
115	chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
116	*plenp = PEEK_U32(buf);
117	return 0;
118}
119