Integrated ECDSA sign and verify functions.

1 files changed, 97 insertions, 0 deletions

diff --git a/ecc-ecdsa-sign.c b/ecc-ecdsa-sign.c
new file mode 100644
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+/* ecc-ecdsa-sign.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 <stdlib.h>
+
+#include "ecdsa.h"
+#include "ecc-internal.h"
+
+/* Low-level ECDSA signing */
+
+mp_size_t
+ecc_ecdsa_sign_itch (const struct ecc_curve *ecc)
+{
+  /* Needs 3*ecc->size + scratch for ecc_mul_g. */
+  return ECC_ECDSA_SIGN_ITCH (ecc->size);
+}
+
+/* NOTE: Caller should check if r or s is zero. */
+void
+ecc_ecdsa_sign (const struct ecc_curve *ecc,
+		const mp_limb_t *zp,
+		/* Random nonce, must be invertible mod ecc group
+		   order. */
+		const mp_limb_t *kp,
+		unsigned length, const uint8_t *digest,
+		mp_limb_t *rp, mp_limb_t *sp,
+		mp_limb_t *scratch)
+{
+  mp_limb_t cy;
+#define P	    scratch
+#define kinv	    scratch                /* Needs 5*ecc->size for computation */
+#define hp	    (scratch  + ecc->size) /* NOTE: ecc->size + 1 limbs! */
+#define tp	    (scratch + 2*ecc->size)
+  /* Procedure, according to RFC 6090, "KT-I". q denotes the group
+     order.
+
+     1. k <-- uniformly random, 0 < k < q
+
+     2. R <-- (r_x, r_y) = k g
+
+     3. s1 <-- r_x mod q
+
+     4. s2 <-- (h + z*s1)/k mod q.
+  */
+
+  ecc_mul_g (ecc, P, kp, P + 3*ecc->size);
+  /* x coordinate only */
+  ecc_j_to_a (ecc, 3, rp, P, P + 3*ecc->size);
+
+  /* We need to reduce x coordinate mod ecc->q. It should already
+     be < 2*ecc->q, so one subtraction should suffice. */
+  cy = mpn_sub_n (scratch, rp, ecc->q, ecc->size);
+  cnd_copy (cy == 0, rp, scratch, ecc->size);
+
+  /* Invert k, uses 5 * ecc->size including scratch */
+  mpn_copyi (hp, kp, ecc->size);
+  ecc_modq_inv (ecc, kinv, hp, tp);
+  
+  /* Process hash digest */
+  ecc_hash (ecc, hp, length, digest);
+
+  ecc_modq_mul (ecc, tp, zp, rp);
+  ecc_modq_add (ecc, hp, hp, tp);
+  ecc_modq_mul (ecc, tp, hp, kinv);
+
+  mpn_copyi (sp, tp, ecc->size);
+#undef P
+#undef hp
+#undef kinv
+#undef tp
+}