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Damien Millerd4a8b7e1999-10-27 13:42:43 +10001/*
Damien Millerd4a8b7e1999-10-27 13:42:43 +10002 * Cryptographic attack detector for ssh - source code
3 *
4 * Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
5 *
6 * All rights reserved. Redistribution and use in source and binary
7 * forms, with or without modification, are permitted provided that
8 * this copyright notice is retained.
9 *
10 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
11 * WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE
12 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR
13 * CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS
14 * SOFTWARE.
15 *
16 * Ariel Futoransky <futo@core-sdi.com>
Damien Miller95def091999-11-25 00:26:21 +110017 * <http://www.core-sdi.com>
18 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100019
20#include "includes.h"
Ben Lindstrom05764b92002-03-05 01:53:02 +000021
Damien Millerd4a8b7e1999-10-27 13:42:43 +100022#include "deattack.h"
Ben Lindstrom226cfa02001-01-22 05:34:40 +000023#include "log.h"
Damien Millerd4a8b7e1999-10-27 13:42:43 +100024#include "crc32.h"
25#include "getput.h"
26#include "xmalloc.h"
27
28/* SSH Constants */
Damien Miller95def091999-11-25 00:26:21 +110029#define SSH_MAXBLOCKS (32 * 1024)
30#define SSH_BLOCKSIZE (8)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100031
32/* Hashing constants */
Damien Miller95def091999-11-25 00:26:21 +110033#define HASH_MINSIZE (8 * 1024)
34#define HASH_ENTRYSIZE (2)
35#define HASH_FACTOR(x) ((x)*3/2)
36#define HASH_UNUSEDCHAR (0xff)
37#define HASH_UNUSED (0xffff)
Damien Miller9f0f5c62001-12-21 14:45:46 +110038#define HASH_IV (0xfffe)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100039
Damien Miller95def091999-11-25 00:26:21 +110040#define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100041
42
43/* Hash function (Input keys are cipher results) */
Damien Miller95def091999-11-25 00:26:21 +110044#define HASH(x) GET_32BIT(x)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100045
Ben Lindstrom204e4882001-03-05 06:47:00 +000046#define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
Damien Millerd4a8b7e1999-10-27 13:42:43 +100047
Ben Lindstrombba81212001-06-25 05:01:22 +000048static void
Damien Miller95def091999-11-25 00:26:21 +110049crc_update(u_int32_t *a, u_int32_t b)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100050{
Damien Miller95def091999-11-25 00:26:21 +110051 b ^= *a;
Damien Miller2dbbf8e2006-03-26 00:11:46 +110052 *a = ssh_crc32((u_char *)&b, sizeof(b));
Damien Millerd4a8b7e1999-10-27 13:42:43 +100053}
54
Damien Miller95def091999-11-25 00:26:21 +110055/* detect if a block is used in a particular pattern */
Ben Lindstrombba81212001-06-25 05:01:22 +000056static int
Damien Miller2dbbf8e2006-03-26 00:11:46 +110057check_crc(u_char *S, u_char *buf, u_int32_t len)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100058{
Damien Miller95def091999-11-25 00:26:21 +110059 u_int32_t crc;
Ben Lindstrom46c16222000-12-22 01:43:59 +000060 u_char *c;
Damien Millerd4a8b7e1999-10-27 13:42:43 +100061
Damien Miller95def091999-11-25 00:26:21 +110062 crc = 0;
Damien Miller95def091999-11-25 00:26:21 +110063 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
64 if (!CMP(S, c)) {
65 crc_update(&crc, 1);
66 crc_update(&crc, 0);
67 } else {
68 crc_update(&crc, 0);
69 crc_update(&crc, 0);
70 }
71 }
72 return (crc == 0);
Damien Millerd4a8b7e1999-10-27 13:42:43 +100073}
74
75
Damien Miller95def091999-11-25 00:26:21 +110076/* Detect a crc32 compensation attack on a packet */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100077int
Damien Miller2dbbf8e2006-03-26 00:11:46 +110078detect_attack(u_char *buf, u_int32_t len)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100079{
Damien Miller95def091999-11-25 00:26:21 +110080 static u_int16_t *h = (u_int16_t *) NULL;
Ben Lindstromf2de06b2000-11-05 05:42:36 +000081 static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
Ben Lindstrom70a290c2001-12-06 16:39:56 +000082 u_int32_t i, j;
Damien Miller95def091999-11-25 00:26:21 +110083 u_int32_t l;
Ben Lindstrom70a290c2001-12-06 16:39:56 +000084 u_char *c;
Ben Lindstrom46c16222000-12-22 01:43:59 +000085 u_char *d;
Damien Millerd4a8b7e1999-10-27 13:42:43 +100086
Damien Miller95def091999-11-25 00:26:21 +110087 if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
88 len % SSH_BLOCKSIZE != 0) {
89 fatal("detect_attack: bad length %d", len);
Damien Millerd4a8b7e1999-10-27 13:42:43 +100090 }
Damien Miller95def091999-11-25 00:26:21 +110091 for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
92 ;
Damien Millerd4a8b7e1999-10-27 13:42:43 +100093
Damien Miller95def091999-11-25 00:26:21 +110094 if (h == NULL) {
95 debug("Installing crc compensation attack detector.");
Darren Tuckerfb16b242003-09-22 21:04:23 +100096 h = (u_int16_t *) xmalloc(l * HASH_ENTRYSIZE);
Damien Miller95def091999-11-25 00:26:21 +110097 n = l;
Damien Miller95def091999-11-25 00:26:21 +110098 } else {
99 if (l > n) {
Darren Tuckerfb16b242003-09-22 21:04:23 +1000100 h = (u_int16_t *) xrealloc(h, l * HASH_ENTRYSIZE);
Damien Miller95def091999-11-25 00:26:21 +1100101 n = l;
Damien Miller95def091999-11-25 00:26:21 +1100102 }
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000103 }
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000104
Damien Miller95def091999-11-25 00:26:21 +1100105 if (len <= HASH_MINBLOCKS) {
106 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
Damien Miller95def091999-11-25 00:26:21 +1100107 for (d = buf; d < c; d += SSH_BLOCKSIZE) {
108 if (!CMP(c, d)) {
Damien Miller2dbbf8e2006-03-26 00:11:46 +1100109 if ((check_crc(c, buf, len)))
Damien Miller95def091999-11-25 00:26:21 +1100110 return (DEATTACK_DETECTED);
111 else
112 break;
113 }
114 }
115 }
116 return (DEATTACK_OK);
117 }
118 memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
119
Damien Miller95def091999-11-25 00:26:21 +1100120 for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
121 for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
Damien Miller9f0f5c62001-12-21 14:45:46 +1100122 i = (i + 1) & (n - 1)) {
Damien Miller2dbbf8e2006-03-26 00:11:46 +1100123 if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
124 if (check_crc(c, buf, len))
Damien Miller95def091999-11-25 00:26:21 +1100125 return (DEATTACK_DETECTED);
126 else
127 break;
128 }
129 }
130 h[i] = j;
131 }
132 return (DEATTACK_OK);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000133}