Annotation of src/usr.bin/ssh/deattack.c, Revision 1.27
1.27 ! djm 1: /* $OpenBSD: deattack.c,v 1.26 2006/03/25 13:17:01 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"
1.18 stevesk 22:
1.1 dugsong 23: #include "deattack.h"
1.12 markus 24: #include "log.h"
1.3 markus 25: #include "crc32.h"
1.1 dugsong 26: #include "xmalloc.h"
1.27 ! djm 27: #include "misc.h"
1.1 dugsong 28:
29: /* SSH Constants */
1.5 markus 30: #define SSH_MAXBLOCKS (32 * 1024)
31: #define SSH_BLOCKSIZE (8)
1.1 dugsong 32:
33: /* Hashing constants */
1.5 markus 34: #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)
1.17 deraadt 39: #define HASH_IV (0xfffe)
1.1 dugsong 40:
1.5 markus 41: #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
1.1 dugsong 42:
43:
44: /* Hash function (Input keys are cipher results) */
1.27 ! djm 45: #define HASH(x) get_u32(x)
1.1 dugsong 46:
1.13 deraadt 47: #define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
1.1 dugsong 48:
1.14 itojun 49: static void
1.5 markus 50: crc_update(u_int32_t *a, u_int32_t b)
1.1 dugsong 51: {
1.5 markus 52: b ^= *a;
1.22 deraadt 53: *a = ssh_crc32((u_char *)&b, sizeof(b));
1.1 dugsong 54: }
55:
1.5 markus 56: /* detect if a block is used in a particular pattern */
1.14 itojun 57: static int
1.23 djm 58: check_crc(u_char *S, u_char *buf, u_int32_t len)
1.1 dugsong 59: {
1.5 markus 60: u_int32_t crc;
1.11 markus 61: u_char *c;
1.1 dugsong 62:
1.5 markus 63: crc = 0;
64: 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);
1.1 dugsong 74: }
75:
76:
1.5 markus 77: /* Detect a crc32 compensation attack on a packet */
1.1 dugsong 78: int
1.23 djm 79: detect_attack(u_char *buf, u_int32_t len)
1.1 dugsong 80: {
1.5 markus 81: static u_int16_t *h = (u_int16_t *) NULL;
1.10 markus 82: static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
1.15 mpech 83: u_int32_t i, j;
1.5 markus 84: u_int32_t l;
1.15 mpech 85: u_char *c;
1.11 markus 86: u_char *d;
1.5 markus 87:
88: if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
89: len % SSH_BLOCKSIZE != 0) {
90: fatal("detect_attack: bad length %d", len);
91: }
92: for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
93: ;
1.1 dugsong 94:
1.5 markus 95: if (h == NULL) {
96: debug("Installing crc compensation attack detector.");
1.24 djm 97: h = (u_int16_t *) xcalloc(l, HASH_ENTRYSIZE);
1.5 markus 98: n = l;
99: } else {
100: if (l > n) {
1.25 djm 101: h = (u_int16_t *)xrealloc(h, l, HASH_ENTRYSIZE);
1.5 markus 102: n = l;
103: }
104: }
105:
106: if (len <= HASH_MINBLOCKS) {
107: for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
108: for (d = buf; d < c; d += SSH_BLOCKSIZE) {
109: if (!CMP(c, d)) {
1.23 djm 110: if ((check_crc(c, buf, len)))
1.5 markus 111: return (DEATTACK_DETECTED);
112: else
113: break;
114: }
115: }
116: }
117: return (DEATTACK_OK);
118: }
119: memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
120:
121: for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
122: for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
1.17 deraadt 123: i = (i + 1) & (n - 1)) {
1.23 djm 124: if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
125: if (check_crc(c, buf, len))
1.5 markus 126: return (DEATTACK_DETECTED);
127: else
128: break;
129: }
130: }
131: h[i] = j;
132: }
133: return (DEATTACK_OK);
1.1 dugsong 134: }
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