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
31 int
chachapoly_init(struct chachapoly_ctx * ctx,const u_char * key,u_int keylen)32 chachapoly_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 */
51 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)52 chachapoly_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 */
106 int
chachapoly_get_length(struct chachapoly_ctx * ctx,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)107 chachapoly_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