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Damien Miller57c30112006-03-26 14:24:48 +11001/* $OpenBSD: deattack.c,v 1.26 2006/03/25 13:17:01 djm Exp $ */
Damien Millerd4a8b7e1999-10-27 13:42:43 +10002/*
Damien Millerd4a8b7e1999-10-27 13:42:43 +10003 * Cryptographic attack detector for ssh - source code
4 *
5 * Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
6 *
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.
10 *
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
15 * SOFTWARE.
16 *
17 * Ariel Futoransky <futo@core-sdi.com>
Damien Miller95def091999-11-25 00:26:21 +110018 * <http://www.core-sdi.com>
19 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100020
21#include "includes.h"
Ben Lindstrom05764b92002-03-05 01:53:02 +000022
Damien Millerd4a8b7e1999-10-27 13:42:43 +100023#include "deattack.h"
Ben Lindstrom226cfa02001-01-22 05:34:40 +000024#include "log.h"
Damien Millerd4a8b7e1999-10-27 13:42:43 +100025#include "crc32.h"
26#include "getput.h"
27#include "xmalloc.h"
28
29/* SSH Constants */
Damien Miller95def091999-11-25 00:26:21 +110030#define SSH_MAXBLOCKS (32 * 1024)
31#define SSH_BLOCKSIZE (8)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100032
33/* Hashing constants */
Damien Miller95def091999-11-25 00:26:21 +110034#define HASH_MINSIZE (8 * 1024)
35#define HASH_ENTRYSIZE (2)
36#define HASH_FACTOR(x) ((x)*3/2)
37#define HASH_UNUSEDCHAR (0xff)
38#define HASH_UNUSED (0xffff)
Damien Miller9f0f5c62001-12-21 14:45:46 +110039#define HASH_IV (0xfffe)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100040
Damien Miller95def091999-11-25 00:26:21 +110041#define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100042
43
44/* Hash function (Input keys are cipher results) */
Damien Miller95def091999-11-25 00:26:21 +110045#define HASH(x) GET_32BIT(x)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100046
Ben Lindstrom204e4882001-03-05 06:47:00 +000047#define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
Damien Millerd4a8b7e1999-10-27 13:42:43 +100048
Ben Lindstrombba81212001-06-25 05:01:22 +000049static void
Damien Miller95def091999-11-25 00:26:21 +110050crc_update(u_int32_t *a, u_int32_t b)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100051{
Damien Miller95def091999-11-25 00:26:21 +110052 b ^= *a;
Damien Miller2dbbf8e2006-03-26 00:11:46 +110053 *a = ssh_crc32((u_char *)&b, sizeof(b));
Damien Millerd4a8b7e1999-10-27 13:42:43 +100054}
55
Damien Miller95def091999-11-25 00:26:21 +110056/* detect if a block is used in a particular pattern */
Ben Lindstrombba81212001-06-25 05:01:22 +000057static int
Damien Miller2dbbf8e2006-03-26 00:11:46 +110058check_crc(u_char *S, u_char *buf, u_int32_t len)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100059{
Damien Miller95def091999-11-25 00:26:21 +110060 u_int32_t crc;
Ben Lindstrom46c16222000-12-22 01:43:59 +000061 u_char *c;
Damien Millerd4a8b7e1999-10-27 13:42:43 +100062
Damien Miller95def091999-11-25 00:26:21 +110063 crc = 0;
Damien Miller95def091999-11-25 00:26:21 +110064 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
65 if (!CMP(S, c)) {
66 crc_update(&crc, 1);
67 crc_update(&crc, 0);
68 } else {
69 crc_update(&crc, 0);
70 crc_update(&crc, 0);
71 }
72 }
73 return (crc == 0);
Damien Millerd4a8b7e1999-10-27 13:42:43 +100074}
75
76
Damien Miller95def091999-11-25 00:26:21 +110077/* Detect a crc32 compensation attack on a packet */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100078int
Damien Miller2dbbf8e2006-03-26 00:11:46 +110079detect_attack(u_char *buf, u_int32_t len)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100080{
Damien Miller95def091999-11-25 00:26:21 +110081 static u_int16_t *h = (u_int16_t *) NULL;
Ben Lindstromf2de06b2000-11-05 05:42:36 +000082 static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
Ben Lindstrom70a290c2001-12-06 16:39:56 +000083 u_int32_t i, j;
Damien Miller95def091999-11-25 00:26:21 +110084 u_int32_t l;
Ben Lindstrom70a290c2001-12-06 16:39:56 +000085 u_char *c;
Ben Lindstrom46c16222000-12-22 01:43:59 +000086 u_char *d;
Damien Millerd4a8b7e1999-10-27 13:42:43 +100087
Damien Miller95def091999-11-25 00:26:21 +110088 if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
89 len % SSH_BLOCKSIZE != 0) {
90 fatal("detect_attack: bad length %d", len);
Damien Millerd4a8b7e1999-10-27 13:42:43 +100091 }
Damien Miller95def091999-11-25 00:26:21 +110092 for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
93 ;
Damien Millerd4a8b7e1999-10-27 13:42:43 +100094
Damien Miller95def091999-11-25 00:26:21 +110095 if (h == NULL) {
96 debug("Installing crc compensation attack detector.");
Damien Miller07d86be2006-03-26 14:19:21 +110097 h = (u_int16_t *) xcalloc(l, HASH_ENTRYSIZE);
Damien Miller95def091999-11-25 00:26:21 +110098 n = l;
Damien Miller95def091999-11-25 00:26:21 +110099 } else {
100 if (l > n) {
Damien Miller36812092006-03-26 14:22:47 +1100101 h = (u_int16_t *)xrealloc(h, l, HASH_ENTRYSIZE);
Damien Miller95def091999-11-25 00:26:21 +1100102 n = l;
Damien Miller95def091999-11-25 00:26:21 +1100103 }
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000104 }
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000105
Damien Miller95def091999-11-25 00:26:21 +1100106 if (len <= HASH_MINBLOCKS) {
107 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
Damien Miller95def091999-11-25 00:26:21 +1100108 for (d = buf; d < c; d += SSH_BLOCKSIZE) {
109 if (!CMP(c, d)) {
Damien Miller2dbbf8e2006-03-26 00:11:46 +1100110 if ((check_crc(c, buf, len)))
Damien Miller95def091999-11-25 00:26:21 +1100111 return (DEATTACK_DETECTED);
112 else
113 break;
114 }
115 }
116 }
117 return (DEATTACK_OK);
118 }
119 memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
120
Damien Miller95def091999-11-25 00:26:21 +1100121 for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
122 for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
Damien Miller9f0f5c62001-12-21 14:45:46 +1100123 i = (i + 1) & (n - 1)) {
Damien Miller2dbbf8e2006-03-26 00:11:46 +1100124 if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
125 if (check_crc(c, buf, len))
Damien Miller95def091999-11-25 00:26:21 +1100126 return (DEATTACK_DETECTED);
127 else
128 break;
129 }
130 }
131 h[i] = j;
132 }
133 return (DEATTACK_OK);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000134}