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-libcrypto.c,v 1.1 2020/04/03 04:32:21 djm Exp $ */
18
19 #include "includes.h"
20 #ifdef WITH_OPENSSL
21 #include "openbsd-compat/openssl-compat.h"
22 #endif
23
24 #if defined(HAVE_EVP_CHACHA20) && !defined(HAVE_BROKEN_CHACHA20)
25
26 #include <sys/types.h>
27 #include <stdarg.h> /* needed for log.h */
28 #include <string.h>
29 #include <stdio.h> /* needed for misc.h */
30
31 #include <openssl/evp.h>
32
33 #include "log.h"
34 #include "sshbuf.h"
35 #include "ssherr.h"
36 #include "cipher-chachapoly.h"
37
38 struct chachapoly_ctx {
39 EVP_CIPHER_CTX *main_evp, *header_evp;
40 };
41
42 struct chachapoly_ctx *
chachapoly_new(const u_char * key,u_int keylen)43 chachapoly_new(const u_char *key, u_int keylen)
44 {
45 struct chachapoly_ctx *ctx;
46
47 if (keylen != (32 + 32)) /* 2 x 256 bit keys */
48 return NULL;
49 if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
50 return NULL;
51 if ((ctx->main_evp = EVP_CIPHER_CTX_new()) == NULL ||
52 (ctx->header_evp = EVP_CIPHER_CTX_new()) == NULL)
53 goto fail;
54 if (!EVP_CipherInit(ctx->main_evp, EVP_chacha20(), key, NULL, 1))
55 goto fail;
56 if (!EVP_CipherInit(ctx->header_evp, EVP_chacha20(), key + 32, NULL, 1))
57 goto fail;
58 if (EVP_CIPHER_CTX_iv_length(ctx->header_evp) != 16)
59 goto fail;
60 return ctx;
61 fail:
62 chachapoly_free(ctx);
63 return NULL;
64 }
65
66 void
chachapoly_free(struct chachapoly_ctx * cpctx)67 chachapoly_free(struct chachapoly_ctx *cpctx)
68 {
69 if (cpctx == NULL)
70 return;
71 EVP_CIPHER_CTX_free(cpctx->main_evp);
72 EVP_CIPHER_CTX_free(cpctx->header_evp);
73 freezero(cpctx, sizeof(*cpctx));
74 }
75
76 /*
77 * chachapoly_crypt() operates as following:
78 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
79 * to 'dest'. The ciphertext here is treated as additional authenticated
80 * data for MAC calculation.
81 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
82 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
83 * tag. This tag is written on encryption and verified on decryption.
84 */
85 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)86 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
87 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
88 {
89 u_char seqbuf[16]; /* layout: u64 counter || u64 seqno */
90 int r = SSH_ERR_INTERNAL_ERROR;
91 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
92
93 /*
94 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
95 * packet sequence number.
96 */
97 memset(seqbuf, 0, sizeof(seqbuf));
98 POKE_U64(seqbuf + 8, seqnr);
99 memset(poly_key, 0, sizeof(poly_key));
100 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
101 EVP_Cipher(ctx->main_evp, poly_key,
102 poly_key, sizeof(poly_key)) < 0) {
103 r = SSH_ERR_LIBCRYPTO_ERROR;
104 goto out;
105 }
106
107 /* If decrypting, check tag before anything else */
108 if (!do_encrypt) {
109 const u_char *tag = src + aadlen + len;
110
111 poly1305_auth(expected_tag, src, aadlen + len, poly_key);
112 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
113 r = SSH_ERR_MAC_INVALID;
114 goto out;
115 }
116 }
117
118 /* Crypt additional data */
119 if (aadlen) {
120 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 1) ||
121 EVP_Cipher(ctx->header_evp, dest, src, aadlen) < 0) {
122 r = SSH_ERR_LIBCRYPTO_ERROR;
123 goto out;
124 }
125 }
126
127 /* Set Chacha's block counter to 1 */
128 seqbuf[0] = 1;
129 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
130 EVP_Cipher(ctx->main_evp, dest + aadlen, src + aadlen, len) < 0) {
131 r = SSH_ERR_LIBCRYPTO_ERROR;
132 goto out;
133 }
134
135 /* If encrypting, calculate and append tag */
136 if (do_encrypt) {
137 poly1305_auth(dest + aadlen + len, dest, aadlen + len,
138 poly_key);
139 }
140 r = 0;
141 out:
142 explicit_bzero(expected_tag, sizeof(expected_tag));
143 explicit_bzero(seqbuf, sizeof(seqbuf));
144 explicit_bzero(poly_key, sizeof(poly_key));
145 return r;
146 }
147
148 /* Decrypt and extract the encrypted packet length */
149 int
chachapoly_get_length(struct chachapoly_ctx * ctx,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)150 chachapoly_get_length(struct chachapoly_ctx *ctx,
151 u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
152 {
153 u_char buf[4], seqbuf[16];
154
155 if (len < 4)
156 return SSH_ERR_MESSAGE_INCOMPLETE;
157 memset(seqbuf, 0, sizeof(seqbuf));
158 POKE_U64(seqbuf + 8, seqnr);
159 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 0))
160 return SSH_ERR_LIBCRYPTO_ERROR;
161 if (EVP_Cipher(ctx->header_evp, buf, (u_char *)cp, sizeof(buf)) < 0)
162 return SSH_ERR_LIBCRYPTO_ERROR;
163 *plenp = PEEK_U32(buf);
164 return 0;
165 }
166 #endif /* defined(HAVE_EVP_CHACHA20) && !defined(HAVE_BROKEN_CHACHA20) */
167