Ethereum address from a signature.

Readme.md

This is an example of receiveing ethereum address from a secp256k1 private key.

Source: witnet/elliptic-curve-solidity#14 (comment)

ethereum_address.sol

pragma solidity ^0.6.0;

import "elliptic-curve-solidity/contracts/EllipticCurve.sol";


/**
 * @title Secp256k1 Elliptic Curve
 * @notice Example of particularization of Elliptic Curve for secp256k1 curve
 * @author Witnet Foundation
 */
contract Secp256k1 {

  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;

  /// @dev Public Key derivation from private key
  /// @param privKey The private key
  /// @return (qx, qy) The Public Key
  function derivePubKey(uint256 privKey) external pure returns (uint256, uint256) {
    return EllipticCurve.ecMul(
      privKey,
      GX,
      GY,
      AA,
      PP
    );
  }

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

    address addr;
    bytes32 hash = keccak256(encodePoint(qx,qy));
    assembly {
        mstore(0, hash)
        addr := mload(0)
    }

    return addr;
  }

  function encodePoint(uint256 _x, uint256 _y) internal pure returns (bytes memory) {
    uint8 prefix = uint8(2 + (_y % 2));

    return abi.encodePacked(prefix, _x);
  }
}