PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
-2)
- The 32-bit CRC compensation attack detector in deattack.c was
- contributed by CORE SDI S.A. under a BSD-style license.
-
- * 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>
-
3)
ssh-keyscan was contributed by David Mazieres under a BSD-style
license.
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
------
-$OpenBSD: LICENCE,v 1.19 2004/08/30 09:18:08 markus Exp $
+$OpenBSD: LICENCE,v 1.20 2017/04/30 23:26:16 djm Exp $
-/* $OpenBSD: deattack.c,v 1.32 2015/01/20 23:14:00 deraadt 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 <string.h>
-#include <stdio.h>
-#include <stdlib.h>
-
-#include "deattack.h"
-#include "crc32.h"
-#include "sshbuf.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) PEEK_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(const u_char *S, const u_char *buf, u_int32_t len)
-{
- u_int32_t crc;
- const 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;
-}
-
-void
-deattack_init(struct deattack_ctx *dctx)
-{
- bzero(dctx, sizeof(*dctx));
- dctx->n = HASH_MINSIZE / HASH_ENTRYSIZE;
-}
-
-/* Detect a crc32 compensation attack on a packet */
-int
-detect_attack(struct deattack_ctx *dctx, const u_char *buf, u_int32_t len)
-{
- u_int32_t i, j, l, same;
- u_int16_t *tmp;
- const u_char *c, *d;
-
- if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
- len % SSH_BLOCKSIZE != 0)
- return DEATTACK_ERROR;
- for (l = dctx->n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
- ;
-
- if (dctx->h == NULL) {
- if ((dctx->h = calloc(l, HASH_ENTRYSIZE)) == NULL)
- return DEATTACK_ERROR;
- dctx->n = l;
- } else {
- if (l > dctx->n) {
- if ((tmp = reallocarray(dctx->h, l, HASH_ENTRYSIZE))
- == NULL) {
- free(dctx->h);
- dctx->h = NULL;
- return DEATTACK_ERROR;
- }
- dctx->h = tmp;
- dctx->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(dctx->h, HASH_UNUSEDCHAR, dctx->n * HASH_ENTRYSIZE);
-
- for (c = buf, same = j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
- for (i = HASH(c) & (dctx->n - 1); dctx->h[i] != HASH_UNUSED;
- i = (i + 1) & (dctx->n - 1)) {
- if (!CMP(c, buf + dctx->h[i] * SSH_BLOCKSIZE)) {
- if (++same > MAX_IDENTICAL)
- return DEATTACK_DOS_DETECTED;
- if (check_crc(c, buf, len))
- return DEATTACK_DETECTED;
- else
- break;
- }
- }
- dctx->h[i] = j;
- }
- return DEATTACK_OK;
-}
-/* $OpenBSD: deattack.h,v 1.11 2015/01/19 19:52:16 markus Exp $ */
-
-/*
- * Cryptographic attack detector for ssh - Header file
- *
- * 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>
- */
-
-#ifndef _DEATTACK_H
-#define _DEATTACK_H
-
-/* Return codes */
-#define DEATTACK_OK 0
-#define DEATTACK_DETECTED 1
-#define DEATTACK_DOS_DETECTED 2
-#define DEATTACK_ERROR 3
-
-struct deattack_ctx {
- u_int16_t *h;
- u_int32_t n;
-};
-
-void deattack_init(struct deattack_ctx *);
-int detect_attack(struct deattack_ctx *, const u_char *, u_int32_t);
-#endif
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