cipher-chachapoly.c revision 262566 
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 1.3 2013/12/15 21:42:35 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 "misc.h"
28#include "cipher-chachapoly.h"
29
30void chachapoly_init(struct chachapoly_ctx *ctx,
31    const u_char *key, u_int keylen)
32{
33	if (keylen != (32 + 32)) /* 2 x 256 bit keys */
34		fatal("%s: invalid keylen %u", __func__, keylen);
35	chacha_keysetup(&ctx->main_ctx, key, 256);
36	chacha_keysetup(&ctx->header_ctx, key + 32, 256);
37}
38
39/*
40 * chachapoly_crypt() operates as following:
41 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
42 * to 'dest'. The ciphertext here is treated as additional authenticated
43 * data for MAC calculation.
44 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
45 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
46 * tag. This tag is written on encryption and verified on decryption.
47 */
48int
49chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
50    const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
51{
52	u_char seqbuf[8];
53	const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
54	u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
55	int r = -1;
56
57	/*
58	 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
59	 * packet sequence number.
60	 */
61	bzero(poly_key, sizeof(poly_key));
62	put_u64(seqbuf, seqnr);
63	chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
64	chacha_encrypt_bytes(&ctx->main_ctx,
65	    poly_key, poly_key, sizeof(poly_key));
66	/* Set Chacha's block counter to 1 */
67	chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
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			goto out;
76	}
77	/* Crypt additional data */
78	if (aadlen) {
79		chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
80		chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
81	}
82	chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
83	    dest + aadlen, len);
84
85	/* If encrypting, calculate and append tag */
86	if (do_encrypt) {
87		poly1305_auth(dest + aadlen + len, dest, aadlen + len,
88		    poly_key);
89	}
90	r = 0;
91
92 out:
93	bzero(expected_tag, sizeof(expected_tag));
94	bzero(seqbuf, sizeof(seqbuf));
95	bzero(poly_key, sizeof(poly_key));
96	return r;
97}
98
99/* Decrypt and extract the encrypted packet length */
100int
101chachapoly_get_length(struct chachapoly_ctx *ctx,
102    u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
103{
104	u_char buf[4], seqbuf[8];
105
106	if (len < 4)
107		return -1; /* Insufficient length */
108	put_u64(seqbuf, seqnr);
109	chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
110	chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
111	*plenp = get_u32(buf);
112	return 0;
113}
114
115