summaryrefslogtreecommitdiff
path: root/deattack.c
diff options
context:
space:
mode:
authorDamien Miller <djm@mindrot.org>1999-10-27 13:42:43 +1000
committerDamien Miller <djm@mindrot.org>1999-10-27 13:42:43 +1000
commitd4a8b7e34dd619a4debf9a206c81db26d1402ea6 (patch)
treea47d770a2f790f40d18b0982d4e55fa7cfb1fa3b /deattack.c
Initial revision
Diffstat (limited to 'deattack.c')
-rw-r--r--deattack.c180
1 files changed, 180 insertions, 0 deletions
diff --git a/deattack.c b/deattack.c
new file mode 100644
index 00000000..d5f8608c
--- /dev/null
+++ b/deattack.c
@@ -0,0 +1,180 @@
+/*
+ * $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);
+}