The NSA's Skipjack block cipher.

[u/mdw/catacomb] / skipjack.h

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+/* -*-c-*-
+ *
+ * $Id: skipjack.h,v 1.1 2000/07/15 15:39:33 mdw Exp $
+ *
+ * The Skipjack block cipher
+ *
+ * (c) 2000 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------* 
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ * 
+ * Catacomb is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+/*----- Revision history --------------------------------------------------* 
+ *
+ * $Log: skipjack.h,v $
+ * Revision 1.1  2000/07/15 15:39:33  mdw
+ * The NSA's Skipjack block cipher.
+ *
+ */
+
+/*----- Notes on the Skipjack block cipher --------------------------------*
+ *
+ * Skipjack was designed by the NSA, as a type II algorithm to be used in the
+ * Clipper system.  It was initially classified, so that it couldn't be used
+ * without the key escrow feature, though a team of `respectable'
+ * cryptographers, including Dorothy Denning, had a quick look at it and
+ * pronounced it `good', as if this was meant to be convincing.  It is
+ * apparently a particular parameterization of a family which includes type I
+ * algorithms.  Since declassification, Biham has discovered a miss-in-the-
+ * middle attack which breaks Skipjack with 31 rounds faster than brute
+ * force.
+ *
+ * This implementation is provided for interest's sake, and possibly for
+ * interoperability, rather than as a good cipher to use.
+ */
+
+#ifndef CATACOMB_SKIPJACK_H
+#define CATACOMB_SKIPJACK_H
+
+#ifdef __cplusplus
+  extern "C" {
+#endif
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <stddef.h>
+
+#include <mLib/bits.h>
+
+/*----- Magical numbers ---------------------------------------------------*/
+
+#define SKIPJACK_BLKSZ 8
+#define SKIPJACK_KEYSZ 10
+#define SKIPJACK_CLASS (N, B, 64)
+
+extern const octet skipjack_keysz[];
+
+/*----- Data structures ---------------------------------------------------*/
+
+typedef struct skipjack_ctx {
+  octet k[10];
+} skipjack_ctx;
+
+/*----- Functions provided ------------------------------------------------*/
+
+/* --- @skipjack_init@ --- *
+ *
+ * Arguments:   @skipjack_ctx *k@ = pointer to key block
+ *              @const void *buf@ = pointer to key buffer
+ *              @size_t sz@ = size of key material
+ *
+ * Returns:     ---
+ *
+ * Use:         Initializes a Skipjack key buffer.  The key buffer must be
+ *             exactly 10 bytes long.
+ */
+
+extern void skipjack_init(skipjack_ctx */*k*/,
+                         const void */*buf*/, size_t /*sz*/);
+
+/* --- @skipjack_eblk@, @skipjack_dblk@ --- *
+ *
+ * Arguments:   @const skipjack_ctx *k@ = pointer to key block
+ *              @const uint32 s[2]@ = pointer to source block
+ *              @uint32 d[2]@ = pointer to skipjacktination block
+ *
+ * Returns:     ---
+ *
+ * Use:         Low-level block encryption and decryption.
+ */
+
+extern void skipjack_eblk(const skipjack_ctx */*k*/,
+                         const uint32 */*s*/, uint32 */*d*/);
+extern void skipjack_dblk(const skipjack_ctx */*k*/,
+                         const uint32 */*s*/, uint32 */*d*/);
+
+/*----- That's all, folks -------------------------------------------------*/
+
+#ifdef __cplusplus
+  }
+#endif
+
+#endif