Initial revision

1 files changed, 180 insertions, 0 deletions

diff --git a/deattack.c b/deattack.c
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+/*
+ * $Id: deattack.c,v 1.1 1999/10/27 03:42:44 damien 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 "deattack.h"
+#include "ssh.h"
+#include "crc32.h"
+#include "getput.h"
+#include "xmalloc.h"
+
+/* 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_32BIT(x)
+
+#define CMP(a,b) (memcmp(a, b, SSH_BLOCKSIZE))
+
+
+void
+crc_update(u_int32_t * a, u_int32_t b)
+{
+  b ^= *a;
+  *a = crc32((unsigned char *) &b, sizeof(b));
+}
+
+/*
+   check_crc
+   detects if a block is used in a particular pattern
+ */
+
+int
+check_crc(unsigned char *S, unsigned char *buf, u_int32_t len, unsigned char *IV)
+{
+  u_int32_t          crc;
+  unsigned char  *c;
+
+  crc = 0;
+  if (IV && !CMP(S, IV))
+  {
+    crc_update(&crc, 1);
+    crc_update(&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_attack
+   Detects a crc32 compensation attack on a packet
+ */
+int
+detect_attack(unsigned char *buf, u_int32_t len, unsigned char *IV)
+{
+  static u_int16_t  *h = (u_int16_t *) NULL;
+  static u_int16_t   n = HASH_MINSIZE / HASH_ENTRYSIZE;
+  register u_int32_t i, j;
+  u_int32_t          l;
+  register unsigned char *c;
+  unsigned char  *d;
+
+
+  assert(len <= (SSH_MAXBLOCKS * SSH_BLOCKSIZE));
+  assert(len % SSH_BLOCKSIZE == 0);
+
+  for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2);
+
+  if (h == NULL)
+  {
+    debug("Installing crc compensation attack detector.");
+    n = l;
+    h = (u_int16_t *) xmalloc(n * HASH_ENTRYSIZE);
+  } else
+  {
+    if (l > n)
+    {
+      n = l;
+      h = (u_int16_t *) xrealloc(h, n * HASH_ENTRYSIZE);
+    }
+  }
+
+
+  if (len <= HASH_MINBLOCKS)
+  {
+    for (c = buf; c < buf + len; c += SSH_BLOCKSIZE)
+    {
+      if (IV && (!CMP(c, IV)))
+      {
+	if ((check_crc(c, buf, len, IV)))
+	  return (DEATTACK_DETECTED);
+	else
+	  break;
+      }
+      for (d = buf; d < c; d += SSH_BLOCKSIZE)
+      {
+	if (!CMP(c, d))
+	{
+	  if ((check_crc(c, buf, len, IV)))
+	    return (DEATTACK_DETECTED);
+	  else
+	    break;
+	}
+      }
+    }
+    return (DEATTACK_OK);
+  }
+  memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
+
+  if (IV)
+    h[HASH(IV) & (n - 1)] = HASH_IV;
+
+
+  for (c = buf, 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 (h[i] == HASH_IV)
+      {
+	if (!CMP(c, IV))
+	{
+	  if (check_crc(c, buf, len, IV))
+	    return (DEATTACK_DETECTED);
+	  else
+	    break;
+	}
+      } else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE))
+      {
+	if (check_crc(c, buf, len, IV))
+	  return (DEATTACK_DETECTED);
+	else
+	  break;
+      }
+    }
+    h[i] = j;
+  }
+
+  return (DEATTACK_OK);
+}