Annotation of src/usr.bin/ssh/deattack.c, Revision 1.24
1.1 dugsong 1: /*
1.2 dugsong 2: * 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>
1.6 deraadt 17: * <http://www.core-sdi.com>
18: */
1.1 dugsong 19:
20: #include "includes.h"
1.18 stevesk 21:
1.1 dugsong 22: #include "deattack.h"
1.12 markus 23: #include "log.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)
1.17 deraadt 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:
1.13 deraadt 46: #define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
1.1 dugsong 47:
1.14 itojun 48: static void
1.5 markus 49: crc_update(u_int32_t *a, u_int32_t b)
1.1 dugsong 50: {
1.5 markus 51: b ^= *a;
1.22 deraadt 52: *a = ssh_crc32((u_char *)&b, sizeof(b));
1.1 dugsong 53: }
54:
1.5 markus 55: /* detect if a block is used in a particular pattern */
1.14 itojun 56: static int
1.23 djm 57: check_crc(u_char *S, u_char *buf, u_int32_t len)
1.1 dugsong 58: {
1.5 markus 59: u_int32_t crc;
1.11 markus 60: u_char *c;
1.1 dugsong 61:
1.5 markus 62: crc = 0;
63: 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);
1.1 dugsong 73: }
74:
75:
1.5 markus 76: /* Detect a crc32 compensation attack on a packet */
1.1 dugsong 77: int
1.23 djm 78: detect_attack(u_char *buf, u_int32_t len)
1.1 dugsong 79: {
1.5 markus 80: static u_int16_t *h = (u_int16_t *) NULL;
1.10 markus 81: static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
1.15 mpech 82: u_int32_t i, j;
1.5 markus 83: u_int32_t l;
1.15 mpech 84: u_char *c;
1.11 markus 85: u_char *d;
1.5 markus 86:
87: if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
88: len % SSH_BLOCKSIZE != 0) {
89: fatal("detect_attack: bad length %d", len);
90: }
91: for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
92: ;
1.1 dugsong 93:
1.5 markus 94: if (h == NULL) {
95: debug("Installing crc compensation attack detector.");
1.24 ! djm 96: h = (u_int16_t *) xcalloc(l, HASH_ENTRYSIZE);
1.5 markus 97: n = l;
98: } else {
99: if (l > n) {
1.19 markus 100: h = (u_int16_t *) xrealloc(h, l * HASH_ENTRYSIZE);
1.5 markus 101: n = l;
102: }
103: }
104:
105: if (len <= HASH_MINBLOCKS) {
106: for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
107: for (d = buf; d < c; d += SSH_BLOCKSIZE) {
108: if (!CMP(c, d)) {
1.23 djm 109: if ((check_crc(c, buf, len)))
1.5 markus 110: return (DEATTACK_DETECTED);
111: else
112: break;
113: }
114: }
115: }
116: return (DEATTACK_OK);
117: }
118: memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
119:
120: for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
121: for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
1.17 deraadt 122: i = (i + 1) & (n - 1)) {
1.23 djm 123: if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
124: if (check_crc(c, buf, len))
1.5 markus 125: return (DEATTACK_DETECTED);
126: else
127: break;
128: }
129: }
130: h[i] = j;
131: }
132: return (DEATTACK_OK);
1.1 dugsong 133: }
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