1 /* $OpenBSD: deattack.c,v 1.29 2006/08/03 03:34:42 deraadt Exp $ */
3 * Cryptographic attack detector for ssh - source code
5 * Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
7 * All rights reserved. Redistribution and use in source and binary
8 * forms, with or without modification, are permitted provided that
9 * this copyright notice is retained.
11 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
12 * WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE
13 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR
14 * CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS
17 * Ariel Futoransky <futo@core-sdi.com>
18 * <http://www.core-sdi.com>
23 #include <sys/types.h>
36 #define SSH_MAXBLOCKS (32 * 1024)
37 #define SSH_BLOCKSIZE (8)
39 /* Hashing constants */
40 #define HASH_MINSIZE (8 * 1024)
41 #define HASH_ENTRYSIZE (2)
42 #define HASH_FACTOR(x) ((x)*3/2)
43 #define HASH_UNUSEDCHAR (0xff)
44 #define HASH_UNUSED (0xffff)
45 #define HASH_IV (0xfffe)
47 #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
50 /* Hash function (Input keys are cipher results) */
51 #define HASH(x) get_u32(x)
53 #define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
56 crc_update(u_int32_t *a, u_int32_t b)
59 *a = ssh_crc32((u_char *)&b, sizeof(b));
62 /* detect if a block is used in a particular pattern */
64 check_crc(u_char *S, u_char *buf, u_int32_t len)
70 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
83 /* Detect a crc32 compensation attack on a packet */
85 detect_attack(u_char *buf, u_int32_t len)
87 static u_int16_t *h = (u_int16_t *) NULL;
88 static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
94 if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
95 len % SSH_BLOCKSIZE != 0) {
96 fatal("detect_attack: bad length %d", len);
98 for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
102 debug("Installing crc compensation attack detector.");
103 h = (u_int16_t *) xcalloc(l, HASH_ENTRYSIZE);
107 h = (u_int16_t *)xrealloc(h, l, HASH_ENTRYSIZE);
112 if (len <= HASH_MINBLOCKS) {
113 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
114 for (d = buf; d < c; d += SSH_BLOCKSIZE) {
116 if ((check_crc(c, buf, len)))
117 return (DEATTACK_DETECTED);
123 return (DEATTACK_OK);
125 memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
127 for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
128 for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
129 i = (i + 1) & (n - 1)) {
130 if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
131 if (check_crc(c, buf, len))
132 return (DEATTACK_DETECTED);
139 return (DEATTACK_OK);