Put ssh back into the repository
Change-Id: I23324372188fa6ed3f93a32b84365f5df6367590
diff --git a/deattack.c b/deattack.c
new file mode 100644
index 0000000..1b37e4d
--- /dev/null
+++ b/deattack.c
@@ -0,0 +1,160 @@
+/* $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);
+}