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Diffstat (limited to 'crypto/openssh/deattack.c')
| -rw-r--r-- | crypto/openssh/deattack.c | 160 |
1 files changed, 0 insertions, 160 deletions
diff --git a/crypto/openssh/deattack.c b/crypto/openssh/deattack.c deleted file mode 100644 index 1b37e4d..0000000 --- a/crypto/openssh/deattack.c +++ /dev/null @@ -1,160 +0,0 @@ -/* $OpenBSD: deattack.c,v 1.30 2006/09/16 19:53:37 djm Exp $ */ -/* - * Cryptographic attack detector for ssh - source code - * - * Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina. - * - * All rights reserved. Redistribution and use in source and binary - * forms, with or without modification, are permitted provided that - * this copyright notice is retained. - * - * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED - * WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE - * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR - * CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS - * SOFTWARE. - * - * Ariel Futoransky <futo@core-sdi.com> - * <http://www.core-sdi.com> - */ - -#include "includes.h" - -#include <sys/types.h> - -#include <string.h> -#include <stdio.h> -#include <stdarg.h> - -#include "xmalloc.h" -#include "deattack.h" -#include "log.h" -#include "crc32.h" -#include "misc.h" - -/* - * CRC attack detection has a worst-case behaviour that is O(N^3) over - * the number of identical blocks in a packet. This behaviour can be - * exploited to create a limited denial of service attack. - * - * However, because we are dealing with encrypted data, identical - * blocks should only occur every 2^35 maximally-sized packets or so. - * Consequently, we can detect this DoS by looking for identical blocks - * in a packet. - * - * The parameter below determines how many identical blocks we will - * accept in a single packet, trading off between attack detection and - * likelihood of terminating a legitimate connection. A value of 32 - * corresponds to an average of 2^40 messages before an attack is - * misdetected - */ -#define MAX_IDENTICAL 32 - -/* SSH Constants */ -#define SSH_MAXBLOCKS (32 * 1024) -#define SSH_BLOCKSIZE (8) - -/* Hashing constants */ -#define HASH_MINSIZE (8 * 1024) -#define HASH_ENTRYSIZE (2) -#define HASH_FACTOR(x) ((x)*3/2) -#define HASH_UNUSEDCHAR (0xff) -#define HASH_UNUSED (0xffff) -#define HASH_IV (0xfffe) - -#define HASH_MINBLOCKS (7*SSH_BLOCKSIZE) - - -/* Hash function (Input keys are cipher results) */ -#define HASH(x) get_u32(x) - -#define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE)) - -static void -crc_update(u_int32_t *a, u_int32_t b) -{ - b ^= *a; - *a = ssh_crc32((u_char *)&b, sizeof(b)); -} - -/* detect if a block is used in a particular pattern */ -static int -check_crc(u_char *S, u_char *buf, u_int32_t len) -{ - u_int32_t crc; - u_char *c; - - crc = 0; - for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { - if (!CMP(S, c)) { - crc_update(&crc, 1); - crc_update(&crc, 0); - } else { - crc_update(&crc, 0); - crc_update(&crc, 0); - } - } - return (crc == 0); -} - - -/* Detect a crc32 compensation attack on a packet */ -int -detect_attack(u_char *buf, u_int32_t len) -{ - static u_int16_t *h = (u_int16_t *) NULL; - static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE; - u_int32_t i, j; - u_int32_t l, same; - u_char *c; - u_char *d; - - if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) || - len % SSH_BLOCKSIZE != 0) { - fatal("detect_attack: bad length %d", len); - } - for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2) - ; - - if (h == NULL) { - debug("Installing crc compensation attack detector."); - h = (u_int16_t *) xcalloc(l, HASH_ENTRYSIZE); - n = l; - } else { - if (l > n) { - h = (u_int16_t *)xrealloc(h, l, HASH_ENTRYSIZE); - n = l; - } - } - - if (len <= HASH_MINBLOCKS) { - for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) { - for (d = buf; d < c; d += SSH_BLOCKSIZE) { - if (!CMP(c, d)) { - if ((check_crc(c, buf, len))) - return (DEATTACK_DETECTED); - else - break; - } - } - } - return (DEATTACK_OK); - } - memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE); - - for (c = buf, same = j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) { - for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED; - i = (i + 1) & (n - 1)) { - if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) { - if (++same > MAX_IDENTICAL) - return (DEATTACK_DOS_DETECTED); - if (check_crc(c, buf, len)) - return (DEATTACK_DETECTED); - else - break; - } - } - h[i] = j; - } - return (DEATTACK_OK); -} |
