| 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 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_X25519_H |
| 29 | #define CATACOMB_X25519_H |
| 30 | |
| 31 | #ifdef __cplusplus |
| 32 | extern "C" { |
| 33 | #endif |
| 34 | |
| 35 | /*----- Notes on the X25519 key-agreement algorithm -----------------------* |
| 36 | * |
| 37 | * This is X25519, as described in Daniel J. Bernstein, `Curve25519: new |
| 38 | * Diffie--Hellman speed records', PKC 2006, |
| 39 | * https://cr.yp.to/ecdh/curve25519-20060209.pdf |
| 40 | * |
| 41 | * Since then, the name `Curve25519' has shifted somewhat, to refer to the |
| 42 | * specific elliptic curve used, and the x-coordinate Diffie--Hellman |
| 43 | * operation is now named `X25519'. |
| 44 | */ |
| 45 | |
| 46 | /*----- Header files ------------------------------------------------------*/ |
| 47 | |
| 48 | #include <mLib/bits.h> |
| 49 | |
| 50 | #ifndef CATACOMB_KEY_H |
| 51 | # include "key.h" |
| 52 | #endif |
| 53 | |
| 54 | /*----- Important constants -----------------------------------------------*/ |
| 55 | |
| 56 | #define X25519_KEYSZ 32u |
| 57 | #define X25519_PUBSZ 32u |
| 58 | #define X25519_OUTSZ 32u |
| 59 | |
| 60 | extern const octet x25519_base[32]; |
| 61 | |
| 62 | /*----- Key fetching ------------------------------------------------------*/ |
| 63 | |
| 64 | typedef struct x25519_priv { key_bin priv, pub; } x25519_priv; |
| 65 | typedef struct x25519_pub { key_bin pub; } x25519_pub; |
| 66 | |
| 67 | extern const key_fetchdef x25519_pubfetch[], x25519_privfetch[]; |
| 68 | #define X25519_PUBFETCHSZ 3 |
| 69 | #define X25519_PRIVFETCHSZ 6 |
| 70 | |
| 71 | /*----- Functions provided ------------------------------------------------*/ |
| 72 | |
| 73 | /* --- @x25519@ --- * |
| 74 | * |
| 75 | * Arguments: @octet zz[X25519_OUTSZ]@ = where to put the result |
| 76 | * @const octet k[X25519_KEYSZ]@ = pointer to private key |
| 77 | * @const octet qx[X25519_PUBSZ]@ = pointer to public value |
| 78 | * |
| 79 | * Returns: --- |
| 80 | * |
| 81 | * Use: Calculates X25519 of @k@ and @qx@. |
| 82 | * |
| 83 | * Note that there is disagreement over whether the most |
| 84 | * significant bit of @qx@ (i.e., the value @qx[31]&0x80@) |
| 85 | * should be ignored or counted towards the represented value. |
| 86 | * Historically implementations respected the bit; later |
| 87 | * convention seems to be to ignore it. This implementation |
| 88 | * honours the bit: a caller who wants to ignore the bit can |
| 89 | * easily clear it, while caller who wants to respect it has a |
| 90 | * difficult job if this function ignores it. |
| 91 | */ |
| 92 | |
| 93 | extern void x25519(octet /*zz*/[X25519_OUTSZ], |
| 94 | const octet /*k*/[X25519_KEYSZ], |
| 95 | const octet /*qx*/[X25519_PUBSZ]); |
| 96 | |
| 97 | /*----- That's all, folks -------------------------------------------------*/ |
| 98 | |
| 99 | #ifdef __cplusplus |
| 100 | } |
| 101 | #endif |
| 102 | |
| 103 | #endif |