Annotation of src/usr.bin/ssh/cipher-chachapoly.c, Revision 1.2
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:
1.2 ! djm 17: /* $OpenBSD$ */
! 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"
25: #include "misc.h"
26: #include "cipher-chachapoly.h"
27:
28: void chachapoly_init(struct chachapoly_ctx *ctx,
29: const u_char *key, u_int keylen)
30: {
31: if (keylen != (32 + 32)) /* 2 x 256 bit keys */
32: fatal("%s: invalid keylen %u", __func__, keylen);
33: chacha_keysetup(&ctx->main_ctx, key, 256);
34: chacha_keysetup(&ctx->header_ctx, key + 32, 256);
35: }
36:
37: /*
38: * chachapoly_crypt() operates as following:
39: * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
40: * Theses bytes are treated as additional authenticated data.
41: * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
42: * Use POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the
43: * authentication tag.
44: * This tag is written on encryption and verified on decryption.
45: * Both 'aadlen' and 'authlen' can be set to 0.
46: */
47: int
48: chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
49: const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
50: {
51: u_char seqbuf[8];
52: u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB. little-endian */
53: u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
54: int r = -1;
55:
56: /*
57: * Run ChaCha20 once to generate the Poly1305 key. The IV is the
58: * packet sequence number.
59: */
60: bzero(poly_key, sizeof(poly_key));
61: put_u64(seqbuf, seqnr);
62: chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
63: chacha_encrypt_bytes(&ctx->main_ctx,
64: poly_key, poly_key, sizeof(poly_key));
65: /* Set Chacha's block counter to 1 */
66: chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
67:
68: /* If decrypting, check tag before anything else */
69: if (!do_encrypt) {
70: const u_char *tag = src + aadlen + len;
71:
72: poly1305_auth(expected_tag, src, aadlen + len, poly_key);
73: if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0)
74: goto out;
75: }
76: /* Crypt additional data */
77: if (aadlen) {
78: chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
79: chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
80: }
81: chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
82: dest + aadlen, len);
83:
84: /* If encrypting, calculate and append tag */
85: if (do_encrypt) {
86: poly1305_auth(dest + aadlen + len, dest, aadlen + len,
87: poly_key);
88: }
89: r = 0;
90:
91: out:
92: bzero(expected_tag, sizeof(expected_tag));
93: bzero(seqbuf, sizeof(seqbuf));
94: bzero(poly_key, sizeof(poly_key));
95: return r;
96: }
97:
98: int
99: chachapoly_get_length(struct chachapoly_ctx *ctx,
100: u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
101: {
102: u_char buf[4], seqbuf[8];
103:
104: if (len < 4)
105: return -1; /* Insufficient length */
106: put_u64(seqbuf, seqnr);
107: chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
108: chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
109: *plenp = get_u32(buf);
110: return 0;
111: }
112: