| 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 | /* --- @dsa_nonce@ --- * |
| 65 | * |
| 66 | * Arguments: @mp *d@ = destination integer |
| 67 | * @mp *q@ = order of the DSA group |
| 68 | * @mp *x@ = secret key |
| 69 | * @const octet *m@ = message hash |
| 70 | * @const gchash *ch@ = hash class |
| 71 | * @grand *r@ = random bit source, or null |
| 72 | * |
| 73 | * Returns: A nonce. |
| 74 | * |
| 75 | * Use: Generates a nonce for use in DSA (or another Fiat--Shamir |
| 76 | * signature scheme). |
| 77 | */ |
| 78 | |
| 79 | mp *dsa_nonce(mp *d, mp *q, mp *x, const octet *m, |
| 80 | const gchash *ch, grand *r) |
| 81 | { |
| 82 | uint32 i = 0; |
| 83 | size_t nb = mp_bits(q), n = (nb + 7)/8, j; |
| 84 | size_t bsz = 2*n + 2*ch->hashsz; |
| 85 | octet *b = XS_ALLOC(bsz); |
| 86 | octet *kb = b, *rb = kb + n, *hb = rb + ch->hashsz; |
| 87 | static const char prefix[] = "catacomb-dsa-nonce"; |
| 88 | ghash *h; |
| 89 | |
| 90 | mp_storeb(x, kb, n); |
| 91 | if (r) grand_fill(r, rb, ch->hashsz); |
| 92 | |
| 93 | do { |
| 94 | for (j = 0; j < n; j += ch->hashsz) { |
| 95 | h = GH_INIT(ch); |
| 96 | GH_HASH(h, prefix, sizeof(prefix)); |
| 97 | GH_HASHBUF32(h, kb, n); |
| 98 | GH_HASHBUF32(h, m, ch->hashsz); |
| 99 | if (r) GH_HASHBUF32(h, rb, ch->hashsz); |
| 100 | GH_HASHU32(h, i); |
| 101 | GH_DONE(h, hb + j); |
| 102 | GH_DESTROY(h); |
| 103 | i++; |
| 104 | } |
| 105 | d = mp_loadb(d, hb, n); |
| 106 | d = mp_lsr(d, d, 8*n - nb); |
| 107 | } while (MP_CMP(d, >=, q)); |
| 108 | |
| 109 | memset(b, 0, bsz); XS_FREE(b); |
| 110 | return (d); |
| 111 | } |
| 112 | |
| 113 | /*----- That's all, folks -------------------------------------------------*/ |