2 * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
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.
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.
17 /* $OpenBSD: cipher-chachapoly.c,v 1.8 2016/08/03 05:41:57 djm Exp $ */
21 #include <sys/types.h>
22 #include <stdarg.h> /* needed for log.h */
24 #include <stdio.h> /* needed for misc.h */
29 #include "cipher-chachapoly.h"
32 chachapoly_init(struct chachapoly_ctx
*ctx
,
33 const u_char
*key
, u_int keylen
)
35 if (keylen
!= (32 + 32)) /* 2 x 256 bit keys */
36 return SSH_ERR_INVALID_ARGUMENT
;
37 chacha_keysetup(&ctx
->main_ctx
, key
, 256);
38 chacha_keysetup(&ctx
->header_ctx
, key
+ 32, 256);
43 * chachapoly_crypt() operates as following:
44 * En/decrypt with header key 'aadlen' bytes from 'src', storing result
45 * to 'dest'. The ciphertext here is treated as additional authenticated
46 * data for MAC calculation.
47 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
48 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
49 * tag. This tag is written on encryption and verified on decryption.
52 chachapoly_crypt(struct chachapoly_ctx
*ctx
, u_int seqnr
, u_char
*dest
,
53 const u_char
*src
, u_int len
, u_int aadlen
, u_int authlen
, int do_encrypt
)
56 const u_char one
[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
57 u_char expected_tag
[POLY1305_TAGLEN
], poly_key
[POLY1305_KEYLEN
];
58 int r
= SSH_ERR_INTERNAL_ERROR
;
61 * Run ChaCha20 once to generate the Poly1305 key. The IV is the
62 * packet sequence number.
64 memset(poly_key
, 0, sizeof(poly_key
));
65 POKE_U64(seqbuf
, seqnr
);
66 chacha_ivsetup(&ctx
->main_ctx
, seqbuf
, NULL
);
67 chacha_encrypt_bytes(&ctx
->main_ctx
,
68 poly_key
, poly_key
, sizeof(poly_key
));
70 /* If decrypting, check tag before anything else */
72 const u_char
*tag
= src
+ aadlen
+ len
;
74 poly1305_auth(expected_tag
, src
, aadlen
+ len
, poly_key
);
75 if (timingsafe_bcmp(expected_tag
, tag
, POLY1305_TAGLEN
) != 0) {
76 r
= SSH_ERR_MAC_INVALID
;
81 /* Crypt additional data */
83 chacha_ivsetup(&ctx
->header_ctx
, seqbuf
, NULL
);
84 chacha_encrypt_bytes(&ctx
->header_ctx
, src
, dest
, aadlen
);
87 /* Set Chacha's block counter to 1 */
88 chacha_ivsetup(&ctx
->main_ctx
, seqbuf
, one
);
89 chacha_encrypt_bytes(&ctx
->main_ctx
, src
+ aadlen
,
92 /* If encrypting, calculate and append tag */
94 poly1305_auth(dest
+ aadlen
+ len
, dest
, aadlen
+ len
,
99 explicit_bzero(expected_tag
, sizeof(expected_tag
));
100 explicit_bzero(seqbuf
, sizeof(seqbuf
));
101 explicit_bzero(poly_key
, sizeof(poly_key
));
105 /* Decrypt and extract the encrypted packet length */
107 chachapoly_get_length(struct chachapoly_ctx
*ctx
,
108 u_int
*plenp
, u_int seqnr
, const u_char
*cp
, u_int len
)
110 u_char buf
[4], seqbuf
[8];
113 return SSH_ERR_MESSAGE_INCOMPLETE
;
114 POKE_U64(seqbuf
, seqnr
);
115 chacha_ivsetup(&ctx
->header_ctx
, seqbuf
, NULL
);
116 chacha_encrypt_bytes(&ctx
->header_ctx
, cp
, buf
, 4);
117 *plenp
= PEEK_U32(buf
);