1 /* $OpenBSD: cipher-chachapoly-libcrypto.c,v 1.2 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 <openssl/evp.h>
24
25 #include "log.h"
26 #include "sshbuf.h"
27 #include "ssherr.h"
28 #include "cipher-chachapoly.h"
29
30 struct chachapoly_ctx {
31 EVP_CIPHER_CTX *main_evp, *header_evp;
32 };
33
34 struct chachapoly_ctx *
chachapoly_new(const u_char * key,u_int keylen)35 chachapoly_new(const u_char *key, u_int keylen)
36 {
37 struct chachapoly_ctx *ctx;
38
39 if (keylen != (32 + 32)) /* 2 x 256 bit keys */
40 return NULL;
41 if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
42 return NULL;
43 if ((ctx->main_evp = EVP_CIPHER_CTX_new()) == NULL ||
44 (ctx->header_evp = EVP_CIPHER_CTX_new()) == NULL)
45 goto fail;
46 if (!EVP_CipherInit(ctx->main_evp, EVP_chacha20(), key, NULL, 1))
47 goto fail;
48 if (!EVP_CipherInit(ctx->header_evp, EVP_chacha20(), key + 32, NULL, 1))
49 goto fail;
50 if (EVP_CIPHER_CTX_iv_length(ctx->header_evp) != 16)
51 goto fail;
52 return ctx;
53 fail:
54 chachapoly_free(ctx);
55 return NULL;
56 }
57
58 void
chachapoly_free(struct chachapoly_ctx * cpctx)59 chachapoly_free(struct chachapoly_ctx *cpctx)
60 {
61 if (cpctx == NULL)
62 return;
63 EVP_CIPHER_CTX_free(cpctx->main_evp);
64 EVP_CIPHER_CTX_free(cpctx->header_evp);
65 freezero(cpctx, sizeof(*cpctx));
66 }
67
68 /*
69 * chachapoly_crypt() operates as following:
70 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
71 * to 'dest'. The ciphertext here is treated as additional authenticated
72 * data for MAC calculation.
73 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
74 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
75 * tag. This tag is written on encryption and verified on decryption.
76 */
77 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)78 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
79 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
80 {
81 u_char seqbuf[16]; /* layout: u64 counter || u64 seqno */
82 int r = SSH_ERR_INTERNAL_ERROR;
83 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
84
85 /*
86 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
87 * packet sequence number.
88 */
89 memset(seqbuf, 0, sizeof(seqbuf));
90 POKE_U64(seqbuf + 8, seqnr);
91 memset(poly_key, 0, sizeof(poly_key));
92 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
93 EVP_Cipher(ctx->main_evp, poly_key,
94 poly_key, sizeof(poly_key)) < 0) {
95 r = SSH_ERR_LIBCRYPTO_ERROR;
96 goto out;
97 }
98
99 /* If decrypting, check tag before anything else */
100 if (!do_encrypt) {
101 const u_char *tag = src + aadlen + len;
102
103 poly1305_auth(expected_tag, src, aadlen + len, poly_key);
104 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
105 r = SSH_ERR_MAC_INVALID;
106 goto out;
107 }
108 }
109
110 /* Crypt additional data */
111 if (aadlen) {
112 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 1) ||
113 EVP_Cipher(ctx->header_evp, dest, src, aadlen) < 0) {
114 r = SSH_ERR_LIBCRYPTO_ERROR;
115 goto out;
116 }
117 }
118
119 /* Set Chacha's block counter to 1 */
120 seqbuf[0] = 1;
121 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
122 EVP_Cipher(ctx->main_evp, dest + aadlen, src + aadlen, len) < 0) {
123 r = SSH_ERR_LIBCRYPTO_ERROR;
124 goto out;
125 }
126
127 /* If encrypting, calculate and append tag */
128 if (do_encrypt) {
129 poly1305_auth(dest + aadlen + len, dest, aadlen + len,
130 poly_key);
131 }
132 r = 0;
133 out:
134 explicit_bzero(expected_tag, sizeof(expected_tag));
135 explicit_bzero(seqbuf, sizeof(seqbuf));
136 explicit_bzero(poly_key, sizeof(poly_key));
137 return r;
138 }
139
140 /* Decrypt and extract the encrypted packet length */
141 int
chachapoly_get_length(struct chachapoly_ctx * ctx,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)142 chachapoly_get_length(struct chachapoly_ctx *ctx,
143 u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
144 {
145 u_char buf[4], seqbuf[16];
146
147 if (len < 4)
148 return SSH_ERR_MESSAGE_INCOMPLETE;
149 memset(seqbuf, 0, sizeof(seqbuf));
150 POKE_U64(seqbuf + 8, seqnr);
151 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 0))
152 return SSH_ERR_LIBCRYPTO_ERROR;
153 if (EVP_Cipher(ctx->header_evp, buf, (u_char *)cp, sizeof(buf)) < 0)
154 return SSH_ERR_LIBCRYPTO_ERROR;
155 *plenp = PEEK_U32(buf);
156 return 0;
157 }
158