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8efc0c15 | 1 | /* |
8efc0c15 | 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> | |
5260325f | 17 | * <http://www.core-sdi.com> |
18 | */ | |
8efc0c15 | 19 | |
20 | #include "includes.h" | |
93c3b6de | 21 | |
8efc0c15 | 22 | #include "deattack.h" |
42f11eb2 | 23 | #include "log.h" |
8efc0c15 | 24 | #include "crc32.h" |
25 | #include "getput.h" | |
26 | #include "xmalloc.h" | |
27 | ||
28 | /* SSH Constants */ | |
5260325f | 29 | #define SSH_MAXBLOCKS (32 * 1024) |
30 | #define SSH_BLOCKSIZE (8) | |
8efc0c15 | 31 | |
32 | /* Hashing constants */ | |
5260325f | 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) | |
184eed6a | 38 | #define HASH_IV (0xfffe) |
8efc0c15 | 39 | |
5260325f | 40 | #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE) |
8efc0c15 | 41 | |
42 | ||
43 | /* Hash function (Input keys are cipher results) */ | |
5260325f | 44 | #define HASH(x) GET_32BIT(x) |
8efc0c15 | 45 | |
12bf85ed | 46 | #define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE)) |
8efc0c15 | 47 | |
396c147e | 48 | static void |
5260325f | 49 | crc_update(u_int32_t *a, u_int32_t b) |
8efc0c15 | 50 | { |
5260325f | 51 | b ^= *a; |
1e3b8b07 | 52 | *a = ssh_crc32((u_char *) &b, sizeof(b)); |
8efc0c15 | 53 | } |
54 | ||
5260325f | 55 | /* detect if a block is used in a particular pattern */ |
396c147e | 56 | static int |
1e3b8b07 | 57 | check_crc(u_char *S, u_char *buf, u_int32_t len, |
58 | u_char *IV) | |
8efc0c15 | 59 | { |
5260325f | 60 | u_int32_t crc; |
1e3b8b07 | 61 | u_char *c; |
5260325f | 62 | |
63 | crc = 0; | |
64 | if (IV && !CMP(S, IV)) { | |
65 | crc_update(&crc, 1); | |
66 | crc_update(&crc, 0); | |
67 | } | |
68 | for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { | |
69 | if (!CMP(S, c)) { | |
70 | crc_update(&crc, 1); | |
71 | crc_update(&crc, 0); | |
72 | } else { | |
73 | crc_update(&crc, 0); | |
74 | crc_update(&crc, 0); | |
75 | } | |
76 | } | |
77 | return (crc == 0); | |
8efc0c15 | 78 | } |
79 | ||
80 | ||
5260325f | 81 | /* Detect a crc32 compensation attack on a packet */ |
8efc0c15 | 82 | int |
1e3b8b07 | 83 | detect_attack(u_char *buf, u_int32_t len, u_char *IV) |
8efc0c15 | 84 | { |
5260325f | 85 | static u_int16_t *h = (u_int16_t *) NULL; |
b850ecd9 | 86 | static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE; |
44c2ab73 | 87 | u_int32_t i, j; |
5260325f | 88 | u_int32_t l; |
44c2ab73 | 89 | u_char *c; |
1e3b8b07 | 90 | u_char *d; |
5260325f | 91 | |
92 | if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) || | |
93 | len % SSH_BLOCKSIZE != 0) { | |
94 | fatal("detect_attack: bad length %d", len); | |
95 | } | |
96 | for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2) | |
97 | ; | |
98 | ||
99 | if (h == NULL) { | |
100 | debug("Installing crc compensation attack detector."); | |
c46e584f | 101 | h = (u_int16_t *) xmalloc(l * HASH_ENTRYSIZE); |
5260325f | 102 | n = l; |
5260325f | 103 | } else { |
104 | if (l > n) { | |
c46e584f | 105 | h = (u_int16_t *) xrealloc(h, l * HASH_ENTRYSIZE); |
5260325f | 106 | n = l; |
5260325f | 107 | } |
108 | } | |
109 | ||
110 | if (len <= HASH_MINBLOCKS) { | |
111 | for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { | |
112 | if (IV && (!CMP(c, IV))) { | |
113 | if ((check_crc(c, buf, len, IV))) | |
114 | return (DEATTACK_DETECTED); | |
115 | else | |
116 | break; | |
117 | } | |
118 | for (d = buf; d < c; d += SSH_BLOCKSIZE) { | |
119 | if (!CMP(c, d)) { | |
120 | if ((check_crc(c, buf, len, IV))) | |
121 | return (DEATTACK_DETECTED); | |
122 | else | |
123 | break; | |
124 | } | |
125 | } | |
126 | } | |
127 | return (DEATTACK_OK); | |
8efc0c15 | 128 | } |
5260325f | 129 | memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE); |
130 | ||
131 | if (IV) | |
132 | h[HASH(IV) & (n - 1)] = HASH_IV; | |
133 | ||
134 | for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) { | |
135 | for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED; | |
184eed6a | 136 | i = (i + 1) & (n - 1)) { |
5260325f | 137 | if (h[i] == HASH_IV) { |
138 | if (!CMP(c, IV)) { | |
139 | if (check_crc(c, buf, len, IV)) | |
140 | return (DEATTACK_DETECTED); | |
141 | else | |
142 | break; | |
143 | } | |
144 | } else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) { | |
145 | if (check_crc(c, buf, len, IV)) | |
146 | return (DEATTACK_DETECTED); | |
147 | else | |
148 | break; | |
149 | } | |
150 | } | |
151 | h[i] = j; | |
8efc0c15 | 152 | } |
5260325f | 153 | return (DEATTACK_OK); |
8efc0c15 | 154 | } |