projects / u / mdw / catacomb / blame
| Commit | Line | Data |
|---|---|---|
| c97fbcf9 MW |
1 | /* -*-c-*- |
| 2 | * | |
| 3 | * Useful functions for doing DSA | |
| 4 | * | |
| 5 | * (c) 2008 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 | /*----- Header files ------------------------------------------------------*/ | |
| 29 | ||
| 30 | #include "dsa.h" | |
| 31 | ||
| 32 | /*----- Main code ---------------------------------------------------------*/ | |
| 33 | ||
| 34 | /* --- @dsa_h2n@ --- * | |
| 35 | * | |
| 36 | * Arguments: @mp *d@ = destination integer | |
| 37 | * @mp *r@ = order of the DSA group | |
| 38 | * @const void *h@ = pointer to message hash | |
| 39 | * @size_t hsz@ = size (in bytes) of the hash output | |
| 40 | * | |
| 41 | * Returns: Resulting integer. | |
| 42 | * | |
| 43 | * Use: Converts a hash to an integer in the demented way necessary | |
| 44 | * for DSA/ECDSA. This is, of course, completely insane, but | |
| 45 | * there you go. | |
| 46 | */ | |
| 47 | ||
| 48 | mp *dsa_h2n(mp *d, mp *r, const void *h, size_t hsz) | |
| 49 | { | |
| 50 | size_t n = mp_bits(r); | |
| 51 | size_t l = hsz; | |
| 52 | size_t s = 0; | |
| 53 | ||
| 54 | if (n < 8*l) { | |
| 55 | l = (n + 7)/8; | |
| 56 | s = 8*l - n; | |
| 57 | } | |
| 58 | d = mp_loadb(d, h, l); | |
| 59 | if (s) | |
| 60 | d = mp_lsr(d, d, s); | |
| 61 | return (d); | |
| 62 | } | |
| 63 | ||
| 64 | /*----- That's all, folks -------------------------------------------------*/ |