xref: /openssh-portable/cipher-chachapoly.c (revision 8461a5b3)
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.c,v 1.9 2020/04/03 04:27:03 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 "log.h"
32 #include "sshbuf.h"
33 #include "ssherr.h"
34 #include "cipher-chachapoly.h"
35 
36 struct chachapoly_ctx {
37 	struct chacha_ctx main_ctx, header_ctx;
38 };
39 
40 struct chachapoly_ctx *
chachapoly_new(const u_char * key,u_int keylen)41 chachapoly_new(const u_char *key, u_int keylen)
42 {
43 	struct chachapoly_ctx *ctx;
44 
45 	if (keylen != (32 + 32)) /* 2 x 256 bit keys */
46 		return NULL;
47 	if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
48 		return NULL;
49 	chacha_keysetup(&ctx->main_ctx, key, 256);
50 	chacha_keysetup(&ctx->header_ctx, key + 32, 256);
51 	return ctx;
52 }
53 
54 void
chachapoly_free(struct chachapoly_ctx * cpctx)55 chachapoly_free(struct chachapoly_ctx *cpctx)
56 {
57 	freezero(cpctx, sizeof(*cpctx));
58 }
59 
60 /*
61  * chachapoly_crypt() operates as following:
62  * En/decrypt with header key 'aadlen' bytes from 'src', storing result
63  * to 'dest'. The ciphertext here is treated as additional authenticated
64  * data for MAC calculation.
65  * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
66  * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
67  * tag. This tag is written on encryption and verified on decryption.
68  */
69 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)70 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
71     const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
72 {
73 	u_char seqbuf[8];
74 	const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
75 	u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
76 	int r = SSH_ERR_INTERNAL_ERROR;
77 
78 	/*
79 	 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
80 	 * packet sequence number.
81 	 */
82 	memset(poly_key, 0, sizeof(poly_key));
83 	POKE_U64(seqbuf, seqnr);
84 	chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
85 	chacha_encrypt_bytes(&ctx->main_ctx,
86 	    poly_key, poly_key, sizeof(poly_key));
87 
88 	/* If decrypting, check tag before anything else */
89 	if (!do_encrypt) {
90 		const u_char *tag = src + aadlen + len;
91 
92 		poly1305_auth(expected_tag, src, aadlen + len, poly_key);
93 		if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
94 			r = SSH_ERR_MAC_INVALID;
95 			goto out;
96 		}
97 	}
98 
99 	/* Crypt additional data */
100 	if (aadlen) {
101 		chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
102 		chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
103 	}
104 
105 	/* Set Chacha's block counter to 1 */
106 	chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
107 	chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
108 	    dest + aadlen, len);
109 
110 	/* If encrypting, calculate and append tag */
111 	if (do_encrypt) {
112 		poly1305_auth(dest + aadlen + len, dest, aadlen + len,
113 		    poly_key);
114 	}
115 	r = 0;
116  out:
117 	explicit_bzero(expected_tag, sizeof(expected_tag));
118 	explicit_bzero(seqbuf, sizeof(seqbuf));
119 	explicit_bzero(poly_key, sizeof(poly_key));
120 	return r;
121 }
122 
123 /* Decrypt and extract the encrypted packet length */
124 int
chachapoly_get_length(struct chachapoly_ctx * ctx,u_int * plenp,u_int seqnr,const u_char * cp,u_int len)125 chachapoly_get_length(struct chachapoly_ctx *ctx,
126     u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
127 {
128 	u_char buf[4], seqbuf[8];
129 
130 	if (len < 4)
131 		return SSH_ERR_MESSAGE_INCOMPLETE;
132 	POKE_U64(seqbuf, seqnr);
133 	chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
134 	chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
135 	*plenp = PEEK_U32(buf);
136 	return 0;
137 }
138 
139 #endif /* !defined(HAVE_EVP_CHACHA20) || defined(HAVE_BROKEN_CHACHA20) */
140