Integrated ECDSA sign and verify functions.

1 files changed, 90 insertions, 0 deletions

diff --git a/ecc-random.c b/ecc-random.c
new file mode 100644
index 00000000..acffb573
--- /dev/null
+++ b/ecc-random.c
@@ -0,0 +1,90 @@
+/* ecc-random.c */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2013 Niels Möller
+ *  
+ * The nettle library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or (at your
+ * option) any later version.
+ * 
+ * The nettle library 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 Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with the nettle library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02111-1301, USA.
+ */
+
+/* Development of Nettle's ECC support was funded by Internetfonden. */
+
+#if HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <assert.h>
+
+#include "ecc.h"
+#include "ecc-internal.h"
+#include "gmp-glue.h"
+#include "nettle-internal.h"
+
+static int
+zero_p (const struct ecc_curve *ecc,
+	const mp_limb_t *xp)
+{
+  mp_limb_t t;
+  mp_size_t i;
+
+  for (i = t = 0; i < ecc->size; i++)
+    t |= xp[i];
+
+  return t == 0;
+}
+
+static int
+ecdsa_in_range (const struct ecc_curve *ecc,
+		const mp_limb_t *xp, mp_limb_t *scratch)
+{
+  /* Check if 0 < x < q, with data independent timing. */
+  return !zero_p (ecc, xp)
+    & (mpn_sub_n (scratch, xp, ecc->q, ecc->size) != 0);
+}
+
+void
+ecc_modq_random (const struct ecc_curve *ecc, mp_limb_t *xp,
+		 void *ctx, nettle_random_func *random, mp_limb_t *scratch)
+{
+  uint8_t *buf = (uint8_t *) scratch;
+  unsigned nbytes = (ecc->bit_size + 7)/8;
+
+  /* The bytes ought to fit in the scratch area, unless we have very
+     unusual limb and byte sizes. */
+  assert (nbytes <= ecc->size * sizeof (mp_limb_t));
+
+  do
+    {
+      /* q and p are of the same bitsize. */
+      random (ctx, nbytes, buf);
+      buf[0] &= 0xff >> (nbytes * 8 - ecc->bit_size);
+
+      _mpn_set_base256 (xp, ecc->size, buf, nbytes);
+    }
+  while (!ecdsa_in_range (ecc, xp, scratch));
+}
+
+void
+ecc_scalar_random (struct ecc_scalar *x,
+		   void *random_ctx, nettle_random_func *random)
+{
+  TMP_DECL (scratch, mp_limb_t, ECC_MODQ_RANDOM_ITCH (ECC_MAX_SIZE));
+  TMP_ALLOC (scratch, ECC_MODQ_RANDOM_ITCH (x->ecc->size));
+
+  ecc_modq_random (x->ecc, x->p, random_ctx, random, scratch);
+}
+
+