3 * Useful functions for doing DSA
5 * (c) 2008 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
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.
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.
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,
28 /*----- Header files ------------------------------------------------------*/
32 /*----- Main code ---------------------------------------------------------*/
34 /* --- @dsa_h2n@ --- *
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
41 * Returns: Resulting integer.
43 * Use: Converts a hash to an integer in the demented way necessary
44 * for DSA/ECDSA. This is, of course, completely insane, but
48 mp *dsa_h2n(mp *d, mp *r, const void *h, size_t hsz)
50 size_t n = mp_bits(r);
58 d = mp_loadb(d, h, l);
64 /* --- @dsa_nonce@ --- *
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
75 * Use: Generates a nonce for use in DSA (or another Fiat--Shamir
79 mp *dsa_nonce(mp *d, mp *q, mp *x, const octet *m,
80 const gchash *ch, grand *r)
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";
91 if (r) grand_fill(r, rb, ch->hashsz);
94 for (j = 0; j < n; j += ch->hashsz) {
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);
105 d = mp_loadb(d, hb, n);
106 d = mp_lsr(d, d, 8*n - nb);
107 } while (MP_CMP(d, >=, q));
109 memset(b, 0, bsz); XS_FREE(b);
113 /*----- That's all, folks -------------------------------------------------*/