Introduce secp256k1_scalar_t for future constant-time mod order operations

src/scalar.h

@@ -0,0 +1,54 @@
+// Copyright (c) 2014 Pieter Wuille
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef _SECP256K1_SCALAR_
+#define _SECP256K1_SCALAR_
+
+#include "num.h"
+
+/** A scalar modulo the group order of the secp256k1 curve. */
+typedef struct {
+    secp256k1_num_t n;
+} secp256k1_scalar_t;
+
+/** Initialize a scalar. */
+void static secp256k1_scalar_init(secp256k1_scalar_t *r);
+
+/** Clear a scalar to prevent the leak of sensitive data. */
+void static secp256k1_scalar_clear(secp256k1_scalar_t *r);
+
+/** Free a scalar. */
+void static secp256k1_scalar_free(secp256k1_scalar_t *r);
+
+/** Access bits from a scalar. */
+int static secp256k1_scalar_get_bits(const secp256k1_scalar_t *a, int offset, int count);
+
+/** Set a scalar from a big endian byte array. */
+void static secp256k1_scalar_set_bin(secp256k1_scalar_t *r, const unsigned char *bin, int len, int *overflow);
+
+/** Convert a scalar to a byte array. */
+void static secp256k1_scalar_get_bin(unsigned char *bin, int len, const secp256k1_scalar_t* a);
+
+/** Add two scalars together (modulo the group order). */
+void static secp256k1_scalar_add(secp256k1_scalar_t *r, const secp256k1_scalar_t *a, const secp256k1_scalar_t *b);
+
+/** Multiply two scalars (modulo the group order). */
+void static secp256k1_scalar_mul(secp256k1_scalar_t *r, const secp256k1_scalar_t *a, const secp256k1_scalar_t *b);
+
+/** Compute the inverse of a scalar (modulo the group order). */
+void static secp256k1_scalar_inverse(secp256k1_scalar_t *r, const secp256k1_scalar_t *a);
+
+/** Compute the complement of a scalar (modulo the group order). */
+void static secp256k1_scalar_negate(secp256k1_scalar_t *r, const secp256k1_scalar_t *a);
+
+/** Check whether a scalar equals zero. */
+int static secp256k1_scalar_is_zero(const secp256k1_scalar_t *a);
+
+/** Check whether a scalar is higher than the group order divided by 2. */
+int static secp256k1_scalar_is_high(const secp256k1_scalar_t *a);
+
+/** Convert a scalar to a number. */
+void static secp256k1_scalar_get_num(secp256k1_num_t *r, const secp256k1_scalar_t *a);
+
+#endif