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