Initial revision

[gssapi-openssh.git] / openssh / deattack.c

diff --git a/openssh/deattack.c b/openssh/deattack.c
new file mode 100644 (file)
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+++ b/openssh/deattack.c
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+/*     $OpenBSD: deattack.c,v 1.14 2001/06/23 15:12:18 itojun 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 "log.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))
+
+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_char *IV)
+{
+       u_int32_t crc;
+       u_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 a crc32 compensation attack on a packet */
+int
+detect_attack(u_char *buf, u_int32_t len, u_char *IV)
+{
+       static u_int16_t *h = (u_int16_t *) NULL;
+       static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
+       register u_int32_t i, j;
+       u_int32_t l;
+       register 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.");
+               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);
+}