1 /* $NetBSD: cipher-chachapoly-libcrypto.c,v 1.3 2023/10/25 20:19:57 christos Exp $ */
2 /* $OpenBSD: cipher-chachapoly-libcrypto.c,v 1.2 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-libcrypto.c,v 1.3 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 <openssl/evp.h>
29
30 #include "log.h"
31 #include "sshbuf.h"
32 #include "ssherr.h"
33 #include "cipher-chachapoly.h"
34
35 struct chachapoly_ctx {
36 EVP_CIPHER_CTX *main_evp, *header_evp;
37 };
38
39 struct chachapoly_ctx *
chachapoly_new(const u_char * key,u_int keylen)40 chachapoly_new(const u_char *key, u_int keylen)
41 {
42 struct chachapoly_ctx *ctx;
43
44 if (keylen != (32 + 32)) /* 2 x 256 bit keys */
45 return NULL;
46 if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
47 return NULL;
48 if ((ctx->main_evp = EVP_CIPHER_CTX_new()) == NULL ||
49 (ctx->header_evp = EVP_CIPHER_CTX_new()) == NULL)
50 goto fail;
51 if (!EVP_CipherInit(ctx->main_evp, EVP_chacha20(), key, NULL, 1))
52 goto fail;
53 if (!EVP_CipherInit(ctx->header_evp, EVP_chacha20(), key + 32, NULL, 1))
54 goto fail;
55 if (EVP_CIPHER_CTX_iv_length(ctx->header_evp) != 16)
56 goto fail;
57 return ctx;
58 fail:
59 chachapoly_free(ctx);
60 return NULL;
61 }
62
63 void
chachapoly_free(struct chachapoly_ctx * cpctx)64 chachapoly_free(struct chachapoly_ctx *cpctx)
65 {
66 if (cpctx == NULL)
67 return;
68 EVP_CIPHER_CTX_free(cpctx->main_evp);
69 EVP_CIPHER_CTX_free(cpctx->header_evp);
70 freezero(cpctx, sizeof(*cpctx));
71 }
72
73 /*
74 * chachapoly_crypt() operates as following:
75 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
76 * to 'dest'. The ciphertext here is treated as additional authenticated
77 * data for MAC calculation.
78 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
79 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
80 * tag. This tag is written on encryption and verified on decryption.
81 */
82 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)83 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
84 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
85 {
86 u_char seqbuf[16]; /* layout: u64 counter || u64 seqno */
87 int r = SSH_ERR_INTERNAL_ERROR;
88 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
89
90 /*
91 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
92 * packet sequence number.
93 */
94 memset(seqbuf, 0, sizeof(seqbuf));
95 POKE_U64(seqbuf + 8, seqnr);
96 memset(poly_key, 0, sizeof(poly_key));
97 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
98 EVP_Cipher(ctx->main_evp, poly_key,
99 poly_key, sizeof(poly_key)) < 0) {
100 r = SSH_ERR_LIBCRYPTO_ERROR;
101 goto out;
102 }
103
104 /* If decrypting, check tag before anything else */
105 if (!do_encrypt) {
106 const u_char *tag = src + aadlen + len;
107
108 poly1305_auth(expected_tag, src, aadlen + len, poly_key);
109 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
110 r = SSH_ERR_MAC_INVALID;
111 goto out;
112 }
113 }
114
115 /* Crypt additional data */
116 if (aadlen) {
117 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 1) ||
118 EVP_Cipher(ctx->header_evp, dest, src, aadlen) < 0) {
119 r = SSH_ERR_LIBCRYPTO_ERROR;
120 goto out;
121 }
122 }
123
124 /* Set Chacha's block counter to 1 */
125 seqbuf[0] = 1;
126 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
127 EVP_Cipher(ctx->main_evp, dest + aadlen, src + aadlen, len) < 0) {
128 r = SSH_ERR_LIBCRYPTO_ERROR;
129 goto out;
130 }
131
132 /* If encrypting, calculate and append tag */
133 if (do_encrypt) {
134 poly1305_auth(dest + aadlen + len, dest, aadlen + len,
135 poly_key);
136 }
137 r = 0;
138 out:
139 explicit_bzero(expected_tag, sizeof(expected_tag));
140 explicit_bzero(seqbuf, sizeof(seqbuf));
141 explicit_bzero(poly_key, sizeof(poly_key));
142 return r;
143 }
144
145 /* Decrypt and extract the encrypted packet length */
146 int
chachapoly_get_length(struct chachapoly_ctx * ctx,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)147 chachapoly_get_length(struct chachapoly_ctx *ctx,
148 u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
149 {
150 u_char buf[4], seqbuf[16];
151
152 if (len < 4)
153 return SSH_ERR_MESSAGE_INCOMPLETE;
154 memset(seqbuf, 0, sizeof(seqbuf));
155 POKE_U64(seqbuf + 8, seqnr);
156 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 0))
157 return SSH_ERR_LIBCRYPTO_ERROR;
158 if (EVP_Cipher(ctx->header_evp, buf, (u_char *)cp, sizeof(buf)) < 0)
159 return SSH_ERR_LIBCRYPTO_ERROR;
160 *plenp = PEEK_U32(buf);
161 return 0;
162 }
163