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+/* -*-c-*-
+ *
+ * The X448 key-agreement algorithm
+ *
+ * (c) 2017 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.
+ */
+
+#ifndef CATACOMB_X448_H
+#define CATACOMB_X448_H
+
+#ifdef __cplusplus
+  extern "C" {
+#endif
+
+/*----- Notes on the X448 key-agreement algorithm -------------------------*
+ *
+ * This is X448, as described in RFC7748, based on the elliptic curve defined
+ * in Mike Hamburg, `Ed448-Goldilocks, a new elliptic curve', EUROCRYPT 2016,
+ * https://eprint.iacr.org/2015/625/.
+ *
+ * The RFC-specified operation is simpler than the Diffie--Hellman function
+ * described in Hamburg's paper, since it doesn't involve the `Decaf'
+ * cofactor elimination procedure.  Indeed, it looks very much like X25519
+ * with Hamburg's curve slotted in in place of Bernstein's.
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <mLib/bits.h>
+
+#ifndef CATACOMB_KEY_H
+#  include "key.h"
+#endif
+
+/*----- Key fetching ------------------------------------------------------*/
+
+typedef struct x448_priv { key_bin priv, pub; } x448_priv;
+typedef struct x448_pub { key_bin pub; } x448_pub;
+
+extern const key_fetchdef x448_pubfetch[], x448_privfetch[];
+#define X448_PUBFETCHSZ 3
+#define X448_PRIVFETCHSZ 6
+
+/*----- Important constants -----------------------------------------------*/
+
+#define X448_KEYSZ 56
+#define X448_PUBSZ 56
+#define X448_OUTSZ 56
+
+extern const octet x448_base[56];
+
+/*----- Functions provided ------------------------------------------------*/
+
+/* --- @x448@ --- *
+ *
+ * Arguments:	@octet zz[X448_OUTSZ]@ = where to put the result
+ *		@const octet k[X448_KEYSZ]@ = pointer to private key
+ *		@const octet qx[X448_PUBSZ]@ = pointer to public value
+ *
+ * Returns:	---
+ *
+ * Use:		Calculates X448 of @k@ and @qx@.
+ */
+
+extern void x448(octet /*zz*/[X448_OUTSZ],
+		 const octet /*k*/[X448_KEYSZ],
+		 const octet /*qx*/[X448_PUBSZ]);
+
+/*----- That's all, folks -------------------------------------------------*/
+
+#ifdef __cplusplus
+  }
+#endif
+
+#endif