mdw@git.distorted.org.uk Git - secnet/blob - x25519.h

   1 /* -*-c-*-
   2  *
   3  * The X25519 key-agreement algorithm
   4  *
   5  * (c) 2017 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of secnet.
  11  * See README for full list of copyright holders.
  12  *
  13  * secnet is free software; you can redistribute it and/or modify it
  14  * under the terms of the GNU General Public License as published by
  15  * the Free Software Foundation; either version d of the License, or
  16  * (at your option) any later version.
  17  *
  18  * secnet is distributed in the hope that it will be useful, but
  19  * WITHOUT ANY WARRANTY; without even the implied warranty of
  20  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  21  * General Public License for more details.
  22  *
  23  * You should have received a copy of the GNU General Public License
  24  * version 3 along with secnet; if not, see
  25  * https://www.gnu.org/licenses/gpl.html.
  26  *
  27  * This file was originally part of Catacomb, but has been automatically
  28  * modified for incorporation into secnet: see `import-catacomb-crypto'
  29  * for details.
  30  *
  31  * Catacomb is free software; you can redistribute it and/or modify
  32  * it under the terms of the GNU Library General Public License as
  33  * published by the Free Software Foundation; either version 2 of the
  34  * License, or (at your option) any later version.
  35  *
  36  * Catacomb is distributed in the hope that it will be useful,
  37  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  38  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  39  * GNU Library General Public License for more details.
  40  *
  41  * You should have received a copy of the GNU Library General Public
  42  * License along with Catacomb; if not, write to the Free
  43  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  44  * MA 02111-1307, USA.
  45  */
  46
  47 #ifndef CATACOMB_X25519_H
  48 #define CATACOMB_X25519_H
  49
  50 #ifdef __cplusplus
  51   extern "C" {
  52 #endif
  53
  54 /*----- Notes on the X25519 key-agreement algorithm -----------------------*
  55  *
  56  * This is X25519, as described in Daniel J. Bernstein, `Curve25519: new
  57  * Diffie--Hellman speed records', PKC 2006,
  58  * https://cr.yp.to/ecdh/curve25519-20060209.pdf
  59  *
  60  * Since then, the name `Curve25519' has shifted somewhat, to refer to the
  61  * specific elliptic curve used, and the x-coordinate Diffie--Hellman
  62  * operation is now named `X25519'.
  63  */
  64
  65 /*----- Header files ------------------------------------------------------*/
  66
  67 #include "fake-mLib-bits.h"
  68
  69 /*----- Important constants -----------------------------------------------*/
  70
  71 #define X25519_KEYSZ 32u
  72 #define X25519_PUBSZ 32u
  73 #define X25519_OUTSZ 32u
  74
  75 extern const octet x25519_base[32];
  76
  77 /*----- Functions provided ------------------------------------------------*/
  78
  79 /* --- @x25519@ --- *
  80  *
  81  * Arguments:   @octet zz[X25519_OUTSZ]@ = where to put the result
  82  *              @const octet k[X25519_KEYSZ]@ = pointer to private key
  83  *              @const octet qx[X25519_PUBSZ]@ = pointer to public value
  84  *
  85  * Returns:     ---
  86  *
  87  * Use:         Calculates X25519 of @k@ and @qx@.
  88  *
  89  *              Note that there is disagreement over whether the most
  90  *              significant bit of @qx@ (i.e., the value @qx[31]&0x80@)
  91  *              should be ignored or counted towards the represented value.
  92  *              Historically implementations respected the bit; later
  93  *              convention seems to be to ignore it.  This implementation
  94  *              honours the bit: a caller who wants to ignore the bit can
  95  *              easily clear it, while caller who wants to respect it has a
  96  *              difficult job if this function ignores it.
  97  */
  98
  99 extern void x25519(octet /*zz*/[X25519_OUTSZ],
 100                    const octet /*k*/[X25519_KEYSZ],
 101                    const octet /*qx*/[X25519_PUBSZ]);
 102
 103 /*----- That's all, folks -------------------------------------------------*/
 104
 105 #ifdef __cplusplus
 106   }
 107 #endif
 108
 109 #endif