mdw@git.distorted.org.uk Git - catacomb/blob - pub/x448.h

   1 /* -*-c-*-
   2  *
   3  * The X448 key-agreement algorithm
   4  *
   5  * (c) 2017 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 #ifndef CATACOMB_X448_H
  29 #define CATACOMB_X448_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Notes on the X448 key-agreement algorithm -------------------------*
  36  *
  37  * This is X448, as described in RFC7748, based on the elliptic curve defined
  38  * in Mike Hamburg, `Ed448-Goldilocks, a new elliptic curve', EUROCRYPT 2016,
  39  * https://eprint.iacr.org/2015/625/.  (The curve here is 4-isogenous to
  40  * Hamburg's curve.)
  41  *
  42  * The RFC-specified operation is simpler than the Diffie--Hellman function
  43  * described in Hamburg's paper, since it doesn't involve the `Decaf'
  44  * cofactor elimination procedure.  Indeed, it looks very much like X25519
  45  * with Hamburg's curve slotted in in place of Bernstein's.
  46  */
  47
  48 /*----- Header files ------------------------------------------------------*/
  49
  50 #include <mLib/bits.h>
  51
  52 #ifndef CATACOMB_KEY_H
  53 #  include "key.h"
  54 #endif
  55
  56 /*----- Key fetching ------------------------------------------------------*/
  57
  58 typedef struct x448_priv { key_bin priv, pub; } x448_priv;
  59 typedef struct x448_pub { key_bin pub; } x448_pub;
  60
  61 extern const key_fetchdef x448_pubfetch[], x448_privfetch[];
  62 #define X448_PUBFETCHSZ 3
  63 #define X448_PRIVFETCHSZ 6
  64
  65 /*----- Important constants -----------------------------------------------*/
  66
  67 #define X448_KEYSZ 56
  68 #define X448_PUBSZ 56
  69 #define X448_OUTSZ 56
  70
  71 extern const octet x448_base[56];
  72
  73 /*----- Functions provided ------------------------------------------------*/
  74
  75 /* --- @x448@ --- *
  76  *
  77  * Arguments:   @octet zz[X448_OUTSZ]@ = where to put the result
  78  *              @const octet k[X448_KEYSZ]@ = pointer to private key
  79  *              @const octet qx[X448_PUBSZ]@ = pointer to public value
  80  *
  81  * Returns:     ---
  82  *
  83  * Use:         Calculates X448 of @k@ and @qx@.
  84  */
  85
  86 extern void x448(octet /*zz*/[X448_OUTSZ],
  87                  const octet /*k*/[X448_KEYSZ],
  88                  const octet /*qx*/[X448_PUBSZ]);
  89
  90 /*----- That's all, folks -------------------------------------------------*/
  91
  92 #ifdef __cplusplus
  93   }
  94 #endif
  95
  96 #endif