Annotation of src/usr.bin/ssh/cipher-chachapoly.c, Revision 1.6
1.1 djm 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:
1.6 ! jsing 17: /* $OpenBSD: cipher-chachapoly.c,v 1.5 2014/06/24 01:13:21 djm Exp $ */
1.2 djm 18:
1.1 djm 19: #include <sys/types.h>
20: #include <stdarg.h> /* needed for log.h */
21: #include <string.h>
22: #include <stdio.h> /* needed for misc.h */
23:
24: #include "log.h"
1.5 djm 25: #include "sshbuf.h"
26: #include "ssherr.h"
1.1 djm 27: #include "cipher-chachapoly.h"
28:
1.5 djm 29: int chachapoly_init(struct chachapoly_ctx *ctx,
1.1 djm 30: const u_char *key, u_int keylen)
31: {
32: if (keylen != (32 + 32)) /* 2 x 256 bit keys */
1.5 djm 33: return SSH_ERR_INVALID_ARGUMENT;
1.1 djm 34: chacha_keysetup(&ctx->main_ctx, key, 256);
35: chacha_keysetup(&ctx->header_ctx, key + 32, 256);
1.5 djm 36: return 0;
1.1 djm 37: }
38:
39: /*
40: * chachapoly_crypt() operates as following:
1.3 djm 41: * En/decrypt with header key 'aadlen' bytes from 'src', storing result
42: * to 'dest'. The ciphertext here is treated as additional authenticated
43: * data for MAC calculation.
44: * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
45: * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
46: * tag. This tag is written on encryption and verified on decryption.
1.1 djm 47: */
48: int
49: chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
50: const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
51: {
52: u_char seqbuf[8];
1.3 djm 53: const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
1.1 djm 54: u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
1.5 djm 55: int r = SSH_ERR_INTERNAL_ERROR;
1.1 djm 56:
57: /*
58: * Run ChaCha20 once to generate the Poly1305 key. The IV is the
59: * packet sequence number.
60: */
1.4 tedu 61: memset(poly_key, 0, sizeof(poly_key));
1.5 djm 62: POKE_U64(seqbuf, seqnr);
1.1 djm 63: chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
64: chacha_encrypt_bytes(&ctx->main_ctx,
65: poly_key, poly_key, sizeof(poly_key));
66:
67: /* If decrypting, check tag before anything else */
68: if (!do_encrypt) {
69: const u_char *tag = src + aadlen + len;
70:
71: poly1305_auth(expected_tag, src, aadlen + len, poly_key);
1.5 djm 72: if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
73: r = SSH_ERR_MAC_INVALID;
1.1 djm 74: goto out;
1.5 djm 75: }
1.1 djm 76: }
1.6 ! jsing 77:
1.1 djm 78: /* Crypt additional data */
1.3 djm 79: if (aadlen) {
1.1 djm 80: chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
81: chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
82: }
1.6 ! jsing 83:
! 84: /* Set Chacha's block counter to 1 */
! 85: chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
1.1 djm 86: chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
87: dest + aadlen, len);
88:
89: /* If encrypting, calculate and append tag */
90: if (do_encrypt) {
91: poly1305_auth(dest + aadlen + len, dest, aadlen + len,
92: poly_key);
93: }
94: r = 0;
95: out:
1.4 tedu 96: explicit_bzero(expected_tag, sizeof(expected_tag));
97: explicit_bzero(seqbuf, sizeof(seqbuf));
98: explicit_bzero(poly_key, sizeof(poly_key));
1.1 djm 99: return r;
100: }
101:
1.3 djm 102: /* Decrypt and extract the encrypted packet length */
1.1 djm 103: int
104: chachapoly_get_length(struct chachapoly_ctx *ctx,
105: u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
106: {
107: u_char buf[4], seqbuf[8];
108:
109: if (len < 4)
1.5 djm 110: return SSH_ERR_MESSAGE_INCOMPLETE;
111: POKE_U64(seqbuf, seqnr);
1.1 djm 112: chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
113: chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
1.5 djm 114: *plenp = PEEK_U32(buf);
1.1 djm 115: return 0;
116: }
117: