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 1.4 2014/01/31 16:39:19 tedu 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
chachapoly_init(struct chachapoly_ctx * ctx,const u_char * key,u_int keylen)30 void 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 */
48 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)49 chachapoly_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 memset(poly_key, 0, 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 explicit_bzero(expected_tag, sizeof(expected_tag));
94 explicit_bzero(seqbuf, sizeof(seqbuf));
95 explicit_bzero(poly_key, sizeof(poly_key));
96 return r;
97 }
98
99 /* Decrypt and extract the encrypted packet length */
100 int
chachapoly_get_length(struct chachapoly_ctx * ctx,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)101 chachapoly_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