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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 |