1 /* $NetBSD: cipher-chachapoly.c,v 1.7 2023/10/25 20:19:57 christos Exp $ */
2 /* $OpenBSD: cipher-chachapoly.c,v 1.10 2023/07/17 05:26:38 djm Exp $ */
3
4 /*
5 * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
6 *
7 * Permission to use, copy, modify, and distribute this software for any
8 * purpose with or without fee is hereby granted, provided that the above
9 * copyright notice and this permission notice appear in all copies.
10 *
11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18 */
19
20 #include "includes.h"
21 __RCSID("$NetBSD: cipher-chachapoly.c,v 1.7 2023/10/25 20:19:57 christos Exp $");
22
23 #include <sys/types.h>
24 #include <stdarg.h> /* needed for log.h */
25 #include <string.h>
26 #include <stdio.h> /* needed for misc.h */
27
28 #include "log.h"
29 #include "sshbuf.h"
30 #include "ssherr.h"
31 #include "cipher-chachapoly.h"
32
33 struct chachapoly_ctx {
34 struct chacha_ctx main_ctx, header_ctx;
35 };
36
37 struct chachapoly_ctx *
chachapoly_new(const u_char * key,u_int keylen)38 chachapoly_new(const u_char *key, u_int keylen)
39 {
40 struct chachapoly_ctx *ctx;
41
42 if (keylen != (32 + 32)) /* 2 x 256 bit keys */
43 return NULL;
44 if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
45 return NULL;
46 chacha_keysetup(&ctx->main_ctx, key, 256);
47 chacha_keysetup(&ctx->header_ctx, key + 32, 256);
48 return ctx;
49 }
50
51 void
chachapoly_free(struct chachapoly_ctx * cpctx)52 chachapoly_free(struct chachapoly_ctx *cpctx)
53 {
54 freezero(cpctx, sizeof(*cpctx));
55 }
56
57 /*
58 * chachapoly_crypt() operates as following:
59 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
60 * to 'dest'. The ciphertext here is treated as additional authenticated
61 * data for MAC calculation.
62 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
63 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
64 * tag. This tag is written on encryption and verified on decryption.
65 */
66 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)67 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
68 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
69 {
70 u_char seqbuf[8];
71 const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
72 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
73 int r = SSH_ERR_INTERNAL_ERROR;
74
75 /*
76 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
77 * packet sequence number.
78 */
79 memset(poly_key, 0, sizeof(poly_key));
80 POKE_U64(seqbuf, seqnr);
81 chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
82 chacha_encrypt_bytes(&ctx->main_ctx,
83 poly_key, poly_key, sizeof(poly_key));
84
85 /* If decrypting, check tag before anything else */
86 if (!do_encrypt) {
87 const u_char *tag = src + aadlen + len;
88
89 poly1305_auth(expected_tag, src, aadlen + len, poly_key);
90 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
91 r = SSH_ERR_MAC_INVALID;
92 goto out;
93 }
94 }
95
96 /* Crypt additional data */
97 if (aadlen) {
98 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
99 chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
100 }
101
102 /* Set Chacha's block counter to 1 */
103 chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
104 chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
105 dest + aadlen, len);
106
107 /* If encrypting, calculate and append tag */
108 if (do_encrypt) {
109 poly1305_auth(dest + aadlen + len, dest, aadlen + len,
110 poly_key);
111 }
112 r = 0;
113 out:
114 explicit_bzero(expected_tag, sizeof(expected_tag));
115 explicit_bzero(seqbuf, sizeof(seqbuf));
116 explicit_bzero(poly_key, sizeof(poly_key));
117 return r;
118 }
119
120 /* Decrypt and extract the encrypted packet length */
121 int
chachapoly_get_length(struct chachapoly_ctx * ctx,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)122 chachapoly_get_length(struct chachapoly_ctx *ctx,
123 u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
124 {
125 u_char buf[4], seqbuf[8];
126
127 if (len < 4)
128 return SSH_ERR_MESSAGE_INCOMPLETE;
129 POKE_U64(seqbuf, seqnr);
130 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
131 chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
132 *plenp = PEEK_U32(buf);
133 return 0;
134 }
135