Ben Lindstrom | 46c1622 | 2000-12-22 01:43:59 +0000 | [diff] [blame] | 1 | /* $OpenBSD: deattack.c,v 1.11 2000/12/19 23:17:56 markus Exp $ */ |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 2 | |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 3 | /* |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 4 | * Cryptographic attack detector for ssh - source code |
| 5 | * |
| 6 | * Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina. |
| 7 | * |
| 8 | * All rights reserved. Redistribution and use in source and binary |
| 9 | * forms, with or without modification, are permitted provided that |
| 10 | * this copyright notice is retained. |
| 11 | * |
| 12 | * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED |
| 13 | * WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE |
| 14 | * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR |
| 15 | * CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS |
| 16 | * SOFTWARE. |
| 17 | * |
| 18 | * Ariel Futoransky <futo@core-sdi.com> |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 19 | * <http://www.core-sdi.com> |
| 20 | */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 21 | |
| 22 | #include "includes.h" |
| 23 | #include "deattack.h" |
| 24 | #include "ssh.h" |
| 25 | #include "crc32.h" |
| 26 | #include "getput.h" |
| 27 | #include "xmalloc.h" |
| 28 | |
| 29 | /* SSH Constants */ |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 30 | #define SSH_MAXBLOCKS (32 * 1024) |
| 31 | #define SSH_BLOCKSIZE (8) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 32 | |
| 33 | /* Hashing constants */ |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 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) |
| 39 | #define HASH_IV (0xfffe) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 40 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 41 | #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 42 | |
| 43 | |
| 44 | /* Hash function (Input keys are cipher results) */ |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 45 | #define HASH(x) GET_32BIT(x) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 46 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 47 | #define CMP(a,b) (memcmp(a, b, SSH_BLOCKSIZE)) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 48 | |
| 49 | |
| 50 | void |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 51 | crc_update(u_int32_t *a, u_int32_t b) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 52 | { |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 53 | b ^= *a; |
Ben Lindstrom | 46c1622 | 2000-12-22 01:43:59 +0000 | [diff] [blame] | 54 | *a = ssh_crc32((u_char *) &b, sizeof(b)); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 55 | } |
| 56 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 57 | /* detect if a block is used in a particular pattern */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 58 | int |
Ben Lindstrom | 46c1622 | 2000-12-22 01:43:59 +0000 | [diff] [blame] | 59 | check_crc(u_char *S, u_char *buf, u_int32_t len, |
| 60 | u_char *IV) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 61 | { |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 62 | u_int32_t crc; |
Ben Lindstrom | 46c1622 | 2000-12-22 01:43:59 +0000 | [diff] [blame] | 63 | u_char *c; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 64 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 65 | crc = 0; |
| 66 | if (IV && !CMP(S, IV)) { |
| 67 | crc_update(&crc, 1); |
| 68 | crc_update(&crc, 0); |
| 69 | } |
| 70 | for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { |
| 71 | if (!CMP(S, c)) { |
| 72 | crc_update(&crc, 1); |
| 73 | crc_update(&crc, 0); |
| 74 | } else { |
| 75 | crc_update(&crc, 0); |
| 76 | crc_update(&crc, 0); |
| 77 | } |
| 78 | } |
| 79 | return (crc == 0); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 80 | } |
| 81 | |
| 82 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 83 | /* Detect a crc32 compensation attack on a packet */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 84 | int |
Ben Lindstrom | 46c1622 | 2000-12-22 01:43:59 +0000 | [diff] [blame] | 85 | detect_attack(u_char *buf, u_int32_t len, u_char *IV) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 86 | { |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 87 | static u_int16_t *h = (u_int16_t *) NULL; |
Ben Lindstrom | f2de06b | 2000-11-05 05:42:36 +0000 | [diff] [blame] | 88 | static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE; |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 89 | register u_int32_t i, j; |
| 90 | u_int32_t l; |
Ben Lindstrom | 46c1622 | 2000-12-22 01:43:59 +0000 | [diff] [blame] | 91 | register u_char *c; |
| 92 | u_char *d; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 93 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 94 | if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) || |
| 95 | len % SSH_BLOCKSIZE != 0) { |
| 96 | fatal("detect_attack: bad length %d", len); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 97 | } |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 98 | for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2) |
| 99 | ; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 100 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 101 | if (h == NULL) { |
| 102 | debug("Installing crc compensation attack detector."); |
| 103 | n = l; |
| 104 | h = (u_int16_t *) xmalloc(n * HASH_ENTRYSIZE); |
| 105 | } else { |
| 106 | if (l > n) { |
| 107 | n = l; |
| 108 | h = (u_int16_t *) xrealloc(h, n * HASH_ENTRYSIZE); |
| 109 | } |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 110 | } |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 111 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 112 | if (len <= HASH_MINBLOCKS) { |
| 113 | for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { |
| 114 | if (IV && (!CMP(c, IV))) { |
| 115 | if ((check_crc(c, buf, len, IV))) |
| 116 | return (DEATTACK_DETECTED); |
| 117 | else |
| 118 | break; |
| 119 | } |
| 120 | for (d = buf; d < c; d += SSH_BLOCKSIZE) { |
| 121 | if (!CMP(c, d)) { |
| 122 | if ((check_crc(c, buf, len, IV))) |
| 123 | return (DEATTACK_DETECTED); |
| 124 | else |
| 125 | break; |
| 126 | } |
| 127 | } |
| 128 | } |
| 129 | return (DEATTACK_OK); |
| 130 | } |
| 131 | memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE); |
| 132 | |
| 133 | if (IV) |
| 134 | h[HASH(IV) & (n - 1)] = HASH_IV; |
| 135 | |
| 136 | for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) { |
| 137 | for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED; |
| 138 | i = (i + 1) & (n - 1)) { |
| 139 | if (h[i] == HASH_IV) { |
| 140 | if (!CMP(c, IV)) { |
| 141 | if (check_crc(c, buf, len, IV)) |
| 142 | return (DEATTACK_DETECTED); |
| 143 | else |
| 144 | break; |
| 145 | } |
| 146 | } else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) { |
| 147 | if (check_crc(c, buf, len, IV)) |
| 148 | return (DEATTACK_DETECTED); |
| 149 | else |
| 150 | break; |
| 151 | } |
| 152 | } |
| 153 | h[i] = j; |
| 154 | } |
| 155 | return (DEATTACK_OK); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 156 | } |