Annotation of src/usr.bin/ssh/deattack.c, Revision 1.28
1.28 ! stevesk 1: /* $OpenBSD: deattack.c,v 1.27 2006/03/30 09:58:15 djm Exp $ */
1.1 dugsong 2: /*
1.2 dugsong 3: * 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>
1.6 deraadt 18: * <http://www.core-sdi.com>
19: */
1.1 dugsong 20:
21: #include "includes.h"
1.28 ! stevesk 22:
! 23: #include <string.h>
1.18 stevesk 24:
1.1 dugsong 25: #include "deattack.h"
1.12 markus 26: #include "log.h"
1.3 markus 27: #include "crc32.h"
1.1 dugsong 28: #include "xmalloc.h"
1.27 djm 29: #include "misc.h"
1.1 dugsong 30:
31: /* SSH Constants */
1.5 markus 32: #define SSH_MAXBLOCKS (32 * 1024)
33: #define SSH_BLOCKSIZE (8)
1.1 dugsong 34:
35: /* Hashing constants */
1.5 markus 36: #define HASH_MINSIZE (8 * 1024)
37: #define HASH_ENTRYSIZE (2)
38: #define HASH_FACTOR(x) ((x)*3/2)
39: #define HASH_UNUSEDCHAR (0xff)
40: #define HASH_UNUSED (0xffff)
1.17 deraadt 41: #define HASH_IV (0xfffe)
1.1 dugsong 42:
1.5 markus 43: #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
1.1 dugsong 44:
45:
46: /* Hash function (Input keys are cipher results) */
1.27 djm 47: #define HASH(x) get_u32(x)
1.1 dugsong 48:
1.13 deraadt 49: #define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
1.1 dugsong 50:
1.14 itojun 51: static void
1.5 markus 52: crc_update(u_int32_t *a, u_int32_t b)
1.1 dugsong 53: {
1.5 markus 54: b ^= *a;
1.22 deraadt 55: *a = ssh_crc32((u_char *)&b, sizeof(b));
1.1 dugsong 56: }
57:
1.5 markus 58: /* detect if a block is used in a particular pattern */
1.14 itojun 59: static int
1.23 djm 60: check_crc(u_char *S, u_char *buf, u_int32_t len)
1.1 dugsong 61: {
1.5 markus 62: u_int32_t crc;
1.11 markus 63: u_char *c;
1.1 dugsong 64:
1.5 markus 65: crc = 0;
66: for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
67: if (!CMP(S, c)) {
68: crc_update(&crc, 1);
69: crc_update(&crc, 0);
70: } else {
71: crc_update(&crc, 0);
72: crc_update(&crc, 0);
73: }
74: }
75: return (crc == 0);
1.1 dugsong 76: }
77:
78:
1.5 markus 79: /* Detect a crc32 compensation attack on a packet */
1.1 dugsong 80: int
1.23 djm 81: detect_attack(u_char *buf, u_int32_t len)
1.1 dugsong 82: {
1.5 markus 83: static u_int16_t *h = (u_int16_t *) NULL;
1.10 markus 84: static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
1.15 mpech 85: u_int32_t i, j;
1.5 markus 86: u_int32_t l;
1.15 mpech 87: u_char *c;
1.11 markus 88: u_char *d;
1.5 markus 89:
90: if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
91: len % SSH_BLOCKSIZE != 0) {
92: fatal("detect_attack: bad length %d", len);
93: }
94: for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
95: ;
1.1 dugsong 96:
1.5 markus 97: if (h == NULL) {
98: debug("Installing crc compensation attack detector.");
1.24 djm 99: h = (u_int16_t *) xcalloc(l, HASH_ENTRYSIZE);
1.5 markus 100: n = l;
101: } else {
102: if (l > n) {
1.25 djm 103: h = (u_int16_t *)xrealloc(h, l, HASH_ENTRYSIZE);
1.5 markus 104: n = l;
105: }
106: }
107:
108: if (len <= HASH_MINBLOCKS) {
109: for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
110: for (d = buf; d < c; d += SSH_BLOCKSIZE) {
111: if (!CMP(c, d)) {
1.23 djm 112: if ((check_crc(c, buf, len)))
1.5 markus 113: return (DEATTACK_DETECTED);
114: else
115: break;
116: }
117: }
118: }
119: return (DEATTACK_OK);
120: }
121: memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
122:
123: for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
124: for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
1.17 deraadt 125: i = (i + 1) & (n - 1)) {
1.23 djm 126: if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
127: if (check_crc(c, buf, len))
1.5 markus 128: return (DEATTACK_DETECTED);
129: else
130: break;
131: }
132: }
133: h[i] = j;
134: }
135: return (DEATTACK_OK);
1.1 dugsong 136: }
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