// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

import "../contracts/EllipticCurve.sol";


/**
 * @title Secp256k1 Elliptic Curve Gas Helper
 * @notice Example of particularization of Elliptic Curve for secp256k1 curve with a non-pure function to analyze gas cost
 * @author Witnet Foundation
 */
contract Secp256k1GasHelper {

  uint256 public constant GX = 0x79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798;
  uint256 public constant GY = 0x483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8;
  uint256 public constant AA = 0;
  uint256 public constant BB = 7;
  uint256 public constant PP = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F;

  function derivePubKey(uint256 privKey) external returns(uint256 qx, uint256 qy) {
    (qx, qy) = EllipticCurve.ecMul(
      privKey,
      GX,
      GY,
      AA,
      PP
    );
  }
}