3 * Cryptographic attack detector for ssh - source code
5 * Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
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.
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
17 * Ariel Futoransky <futo@core-sdi.com>
18 * <http://www.core-sdi.com> */
28 #define SSH_MAXBLOCKS (32 * 1024)
29 #define SSH_BLOCKSIZE (8)
31 /* Hashing constants */
32 #define HASH_MINSIZE (8 * 1024)
33 #define HASH_ENTRYSIZE (2)
34 #define HASH_FACTOR(x) ((x)*3/2)
35 #define HASH_UNUSEDCHAR (0xff)
36 #define HASH_UNUSED (0xffff)
37 #define HASH_IV (0xfffe)
39 #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
42 /* Hash function (Input keys are cipher results) */
43 #define HASH(x) GET_32BIT(x)
45 #define CMP(a,b) (memcmp(a, b, SSH_BLOCKSIZE))
49 crc_update(u_int32_t * a, u_int32_t b)
52 *a = crc32((unsigned char *) &b, sizeof(b));
57 detects if a block is used in a particular pattern
61 check_crc(unsigned char *S, unsigned char *buf, u_int32_t len, unsigned char *IV)
67 if (IV && !CMP(S, IV))
72 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE)
91 Detects a crc32 compensation attack on a packet
94 detect_attack(unsigned char *buf, u_int32_t len, unsigned char *IV)
96 static u_int16_t *h = (u_int16_t *) NULL;
97 static u_int16_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
98 register u_int32_t i, j;
100 register unsigned char *c;
104 assert(len <= (SSH_MAXBLOCKS * SSH_BLOCKSIZE));
105 assert(len % SSH_BLOCKSIZE == 0);
107 for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2);
111 debug("Installing crc compensation attack detector.");
113 h = (u_int16_t *) xmalloc(n * HASH_ENTRYSIZE);
119 h = (u_int16_t *) xrealloc(h, n * HASH_ENTRYSIZE);
124 if (len <= HASH_MINBLOCKS)
126 for (c = buf; c < buf + len; c += SSH_BLOCKSIZE)
128 if (IV && (!CMP(c, IV)))
130 if ((check_crc(c, buf, len, IV)))
131 return (DEATTACK_DETECTED);
135 for (d = buf; d < c; d += SSH_BLOCKSIZE)
139 if ((check_crc(c, buf, len, IV)))
140 return (DEATTACK_DETECTED);
146 return (DEATTACK_OK);
148 memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
151 h[HASH(IV) & (n - 1)] = HASH_IV;
154 for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++)
156 for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
157 i = (i + 1) & (n - 1))
163 if (check_crc(c, buf, len, IV))
164 return (DEATTACK_DETECTED);
168 } else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE))
170 if (check_crc(c, buf, len, IV))
171 return (DEATTACK_DETECTED);
179 return (DEATTACK_OK);