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1.1 dugsong 1: /*
1.6 ! deraadt 2: * $Id: deattack.c,v 1.5 1999/11/23 22:25:53 markus Exp $
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"
22: #include "deattack.h"
23: #include "ssh.h"
1.3 markus 24: #include "crc32.h"
1.1 dugsong 25: #include "getput.h"
26: #include "xmalloc.h"
27:
28: /* SSH Constants */
1.5 markus 29: #define SSH_MAXBLOCKS (32 * 1024)
30: #define SSH_BLOCKSIZE (8)
1.1 dugsong 31:
32: /* Hashing constants */
1.5 markus 33: #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)
38: #define HASH_IV (0xfffe)
1.1 dugsong 39:
1.5 markus 40: #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
1.1 dugsong 41:
42:
43: /* Hash function (Input keys are cipher results) */
1.5 markus 44: #define HASH(x) GET_32BIT(x)
1.1 dugsong 45:
1.5 markus 46: #define CMP(a,b) (memcmp(a, b, SSH_BLOCKSIZE))
1.1 dugsong 47:
48:
49: 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;
53: *a = crc32((unsigned char *) &b, sizeof(b));
1.1 dugsong 54: }
55:
1.5 markus 56: /* detect if a block is used in a particular pattern */
1.1 dugsong 57: int
1.5 markus 58: check_crc(unsigned char *S, unsigned char *buf, u_int32_t len,
59: unsigned char *IV)
1.1 dugsong 60: {
1.5 markus 61: u_int32_t crc;
62: unsigned char *c;
1.1 dugsong 63:
1.5 markus 64: crc = 0;
65: if (IV && !CMP(S, IV)) {
66: crc_update(&crc, 1);
67: crc_update(&crc, 0);
68: }
69: for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
70: if (!CMP(S, c)) {
71: crc_update(&crc, 1);
72: crc_update(&crc, 0);
73: } else {
74: crc_update(&crc, 0);
75: crc_update(&crc, 0);
76: }
77: }
78: return (crc == 0);
1.1 dugsong 79: }
80:
81:
1.5 markus 82: /* Detect a crc32 compensation attack on a packet */
1.1 dugsong 83: int
84: detect_attack(unsigned char *buf, u_int32_t len, unsigned char *IV)
85: {
1.5 markus 86: static u_int16_t *h = (u_int16_t *) NULL;
87: static u_int16_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
88: register u_int32_t i, j;
89: u_int32_t l;
90: register unsigned char *c;
91: unsigned char *d;
92:
93: if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
94: len % SSH_BLOCKSIZE != 0) {
95: fatal("detect_attack: bad length %d", len);
96: }
97: for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
98: ;
1.1 dugsong 99:
1.5 markus 100: if (h == NULL) {
101: debug("Installing crc compensation attack detector.");
102: n = l;
103: h = (u_int16_t *) xmalloc(n * HASH_ENTRYSIZE);
104: } else {
105: if (l > n) {
106: n = l;
107: h = (u_int16_t *) xrealloc(h, n * HASH_ENTRYSIZE);
108: }
109: }
110:
111: if (len <= HASH_MINBLOCKS) {
112: for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
113: if (IV && (!CMP(c, IV))) {
114: if ((check_crc(c, buf, len, IV)))
115: return (DEATTACK_DETECTED);
116: else
117: break;
118: }
119: for (d = buf; d < c; d += SSH_BLOCKSIZE) {
120: if (!CMP(c, d)) {
121: if ((check_crc(c, buf, len, IV)))
122: return (DEATTACK_DETECTED);
123: else
124: break;
125: }
126: }
127: }
128: return (DEATTACK_OK);
129: }
130: memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
131:
132: if (IV)
133: h[HASH(IV) & (n - 1)] = HASH_IV;
134:
135: for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
136: for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
137: i = (i + 1) & (n - 1)) {
138: if (h[i] == HASH_IV) {
139: if (!CMP(c, IV)) {
140: if (check_crc(c, buf, len, IV))
141: return (DEATTACK_DETECTED);
142: else
143: break;
144: }
145: } else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
146: if (check_crc(c, buf, len, IV))
147: return (DEATTACK_DETECTED);
148: else
149: break;
150: }
151: }
152: h[i] = j;
153: }
154: return (DEATTACK_OK);
1.1 dugsong 155: }