| 1 | /* $OpenBSD: deattack.c,v 1.14 2001/06/23 15:12:18 itojun Exp $ */ |
| 2 | |
| 3 | /* |
| 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> |
| 19 | * <http://www.core-sdi.com> |
| 20 | * |
| 21 | * Modified for use in PuTTY by Simon Tatham |
| 22 | */ |
| 23 | |
| 24 | #include <assert.h> |
| 25 | #include "misc.h" |
| 26 | #include "ssh.h" |
| 27 | |
| 28 | typedef unsigned char uchar; |
| 29 | typedef unsigned short uint16; |
| 30 | |
| 31 | /* SSH Constants */ |
| 32 | #define SSH_MAXBLOCKS (32 * 1024) |
| 33 | #define SSH_BLOCKSIZE (8) |
| 34 | |
| 35 | /* Hashing constants */ |
| 36 | #define HASH_MINSIZE (8 * 1024) |
| 37 | #define HASH_ENTRYSIZE (sizeof(uint16)) |
| 38 | #define HASH_FACTOR(x) ((x)*3/2) |
| 39 | #define HASH_UNUSEDCHAR (0xff) |
| 40 | #define HASH_UNUSED (0xffff) |
| 41 | #define HASH_IV (0xfffe) |
| 42 | |
| 43 | #define HASH_MINBLOCKS (7*SSH_BLOCKSIZE) |
| 44 | |
| 45 | /* Hash function (Input keys are cipher results) */ |
| 46 | #define HASH(x) GET_32BIT_MSB_FIRST(x) |
| 47 | |
| 48 | #define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE)) |
| 49 | |
| 50 | uchar ONE[4] = { 1, 0, 0, 0 }; |
| 51 | uchar ZERO[4] = { 0, 0, 0, 0 }; |
| 52 | |
| 53 | struct crcda_ctx { |
| 54 | uint16 *h; |
| 55 | uint32 n; |
| 56 | }; |
| 57 | |
| 58 | void *crcda_make_context(void) |
| 59 | { |
| 60 | struct crcda_ctx *ret = snew(struct crcda_ctx); |
| 61 | ret->h = NULL; |
| 62 | ret->n = HASH_MINSIZE / HASH_ENTRYSIZE; |
| 63 | return ret; |
| 64 | } |
| 65 | |
| 66 | void crcda_free_context(void *handle) |
| 67 | { |
| 68 | struct crcda_ctx *ctx = (struct crcda_ctx *)handle; |
| 69 | if (ctx) { |
| 70 | sfree(ctx->h); |
| 71 | ctx->h = NULL; |
| 72 | sfree(ctx); |
| 73 | } |
| 74 | } |
| 75 | |
| 76 | static void crc_update(uint32 *a, void *b) |
| 77 | { |
| 78 | *a = crc32_update(*a, b, 4); |
| 79 | } |
| 80 | |
| 81 | /* detect if a block is used in a particular pattern */ |
| 82 | static int check_crc(uchar *S, uchar *buf, uint32 len, uchar *IV) |
| 83 | { |
| 84 | uint32 crc; |
| 85 | uchar *c; |
| 86 | |
| 87 | crc = 0; |
| 88 | if (IV && !CMP(S, IV)) { |
| 89 | crc_update(&crc, ONE); |
| 90 | crc_update(&crc, ZERO); |
| 91 | } |
| 92 | for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { |
| 93 | if (!CMP(S, c)) { |
| 94 | crc_update(&crc, ONE); |
| 95 | crc_update(&crc, ZERO); |
| 96 | } else { |
| 97 | crc_update(&crc, ZERO); |
| 98 | crc_update(&crc, ZERO); |
| 99 | } |
| 100 | } |
| 101 | return (crc == 0); |
| 102 | } |
| 103 | |
| 104 | /* Detect a crc32 compensation attack on a packet */ |
| 105 | int detect_attack(void *handle, uchar *buf, uint32 len, uchar *IV) |
| 106 | { |
| 107 | struct crcda_ctx *ctx = (struct crcda_ctx *)handle; |
| 108 | register uint32 i, j; |
| 109 | uint32 l; |
| 110 | register uchar *c; |
| 111 | uchar *d; |
| 112 | |
| 113 | assert(!(len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) || |
| 114 | len % SSH_BLOCKSIZE != 0)); |
| 115 | for (l = ctx->n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2) |
| 116 | ; |
| 117 | |
| 118 | if (ctx->h == NULL) { |
| 119 | ctx->n = l; |
| 120 | ctx->h = snewn(ctx->n, uint16); |
| 121 | } else { |
| 122 | if (l > ctx->n) { |
| 123 | ctx->n = l; |
| 124 | ctx->h = sresize(ctx->h, ctx->n, uint16); |
| 125 | } |
| 126 | } |
| 127 | |
| 128 | if (len <= HASH_MINBLOCKS) { |
| 129 | for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { |
| 130 | if (IV && (!CMP(c, IV))) { |
| 131 | if ((check_crc(c, buf, len, IV))) |
| 132 | return 1; /* attack detected */ |
| 133 | else |
| 134 | break; |
| 135 | } |
| 136 | for (d = buf; d < c; d += SSH_BLOCKSIZE) { |
| 137 | if (!CMP(c, d)) { |
| 138 | if ((check_crc(c, buf, len, IV))) |
| 139 | return 1; /* attack detected */ |
| 140 | else |
| 141 | break; |
| 142 | } |
| 143 | } |
| 144 | } |
| 145 | return 0; /* ok */ |
| 146 | } |
| 147 | memset(ctx->h, HASH_UNUSEDCHAR, ctx->n * HASH_ENTRYSIZE); |
| 148 | |
| 149 | if (IV) |
| 150 | ctx->h[HASH(IV) & (ctx->n - 1)] = HASH_IV; |
| 151 | |
| 152 | for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) { |
| 153 | for (i = HASH(c) & (ctx->n - 1); ctx->h[i] != HASH_UNUSED; |
| 154 | i = (i + 1) & (ctx->n - 1)) { |
| 155 | if (ctx->h[i] == HASH_IV) { |
| 156 | if (!CMP(c, IV)) { |
| 157 | if (check_crc(c, buf, len, IV)) |
| 158 | return 1; /* attack detected */ |
| 159 | else |
| 160 | break; |
| 161 | } |
| 162 | } else if (!CMP(c, buf + ctx->h[i] * SSH_BLOCKSIZE)) { |
| 163 | if (check_crc(c, buf, len, IV)) |
| 164 | return 1; /* attack detected */ |
| 165 | else |
| 166 | break; |
| 167 | } |
| 168 | } |
| 169 | ctx->h[i] = j; |
| 170 | } |
| 171 | return 0; /* ok */ |
| 172 | } |