X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/ba6e6b64033b1f9de49feccb5c9cd438354481f7..0f00dc4c8eb47e67bc0f148c2dd109f73a451e0a:/pub/dsa-misc.c

diff --git a/pub/dsa-misc.c b/pub/dsa-misc.c
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+/* -*-c-*-
+ *
+ * Useful functions for doing DSA
+ *
+ * (c) 2008 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------*
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * Catacomb is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include "dsa.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @dsa_h2n@ --- *
+ *
+ * Arguments:	@mp *d@ = destination integer
+ *		@mp *r@ = order of the DSA group
+ *		@const void *h@ = pointer to message hash
+ *		@size_t hsz@ = size (in bytes) of the hash output
+ *
+ * Returns:	Resulting integer.
+ *
+ * Use:		Converts a hash to an integer in the demented way necessary
+ *		for DSA/ECDSA.  This is, of course, completely insane, but
+ *		there you go.
+ */
+
+mp *dsa_h2n(mp *d, mp *r, const void *h, size_t hsz)
+{
+  size_t n = mp_bits(r);
+  size_t l = hsz;
+  size_t s = 0;
+
+  if (n < 8*l) {
+    l = (n + 7)/8;
+    s = 8*l - n;
+  }
+  d = mp_loadb(d, h, l);
+  if (s)
+    d = mp_lsr(d, d, s);
+  return (d);
+}
+
+/*----- That's all, folks -------------------------------------------------*/