Add the CRC32 compensation attack detector that all other SSH

[u/mdw/putty] / sshcrcda.c

diff --git a/sshcrcda.c b/sshcrcda.c
new file mode 100644 (file)
index 0000000..7b683be
--- /dev/null
+++ b/sshcrcda.c
@@ -0,0 +1,157 @@
+/*     $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>
+ * 
+ * Modified for use in PuTTY by Simon Tatham
+ */
+
+#include <assert.h>
+#include "misc.h"
+#include "ssh.h"
+
+typedef unsigned char uchar;
+typedef unsigned short uint16;
+
+/* SSH Constants */
+#define SSH_MAXBLOCKS  (32 * 1024)
+#define SSH_BLOCKSIZE  (8)
+
+/* Hashing constants */
+#define HASH_MINSIZE   (8 * 1024)
+#define HASH_ENTRYSIZE (sizeof(uint16))
+#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)
+
+#define GET_32BIT_MSB_FIRST(cp) \
+  (((unsigned long)(unsigned char)(cp)[0] << 24) | \
+  ((unsigned long)(unsigned char)(cp)[1] << 16) | \
+  ((unsigned long)(unsigned char)(cp)[2] << 8) | \
+  ((unsigned long)(unsigned char)(cp)[3]))
+
+/* Hash function (Input keys are cipher results) */
+#define HASH(x)                GET_32BIT_MSB_FIRST(x)
+
+#define CMP(a, b)      (memcmp(a, b, SSH_BLOCKSIZE))
+
+uchar ONE[4] = { 1, 0, 0, 0 };
+uchar ZERO[4] = { 0, 0, 0, 0 };
+
+static void crc_update(uint32 *a, void *b)
+{
+    *a = crc32_update(*a, b, 4);
+}
+
+/* detect if a block is used in a particular pattern */
+static int check_crc(uchar *S, uchar *buf, uint32 len, uchar *IV)
+{
+    uint32 crc;
+    uchar *c;
+
+    crc = 0;
+    if (IV && !CMP(S, IV)) {
+        crc_update(&crc, ONE);
+        crc_update(&crc, ZERO);
+    }
+    for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
+        if (!CMP(S, c)) {
+            crc_update(&crc, ONE);
+            crc_update(&crc, ZERO);
+        } else {
+            crc_update(&crc, ZERO);
+            crc_update(&crc, ZERO);
+        }
+    }
+    return (crc == 0);
+}
+
+/* Detect a crc32 compensation attack on a packet */
+int detect_attack(uchar *buf, uint32 len, uchar *IV)
+{
+    static uint16 *h = (uint16 *) NULL;
+    static uint32 n = HASH_MINSIZE / HASH_ENTRYSIZE;
+    register uint32 i, j;
+    uint32 l;
+    register uchar *c;
+    uchar *d;
+
+    assert(!(len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
+             len % SSH_BLOCKSIZE != 0));
+    for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
+        ;
+
+    if (h == NULL) {
+        logevent("Installing CRC compensation attack detector");
+        n = l;
+        h = (uint16 *) smalloc(n * HASH_ENTRYSIZE);
+    } else {
+        if (l > n) {
+            n = l;
+            h = (uint16 *) srealloc(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 1;          /* attack detected */
+                else
+                    break;
+            }
+            for (d = buf; d < c; d += SSH_BLOCKSIZE) {
+                if (!CMP(c, d)) {
+                    if ((check_crc(c, buf, len, IV)))
+                        return 1;      /* attack detected */
+                    else
+                        break;
+                }
+            }
+        }
+        return 0;                      /* 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 1;      /* attack detected */
+                    else
+                        break;
+                }
+            } else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
+                if (check_crc(c, buf, len, IV))
+                    return 1;          /* attack detected */
+                else
+                    break;
+            }
+        }
+        h[i] = j;
+    }
+    return 0;                          /* ok */
+}