[ERC918] PoWの仕組みを利用してトークンの初期配布を行う仕組みを理解しよう！

interface ERC918  {
   
   function mint(uint256 nonce) public returns (bool success);

   function getAdjustmentInterval() public view returns (uint);

   function getChallengeNumber() public view returns (bytes32);

   function getMiningDifficulty() public view returns (uint);

   function getMiningTarget() public view returns (uint);

   function getMiningReward() public view returns (uint);
   
   function decimals() public view returns (uint8);

   event Mint(address indexed from, uint rewardAmount, uint epochCount, bytes32 newChallengeNumber);
}

bytes32 public adjustmentInterval;

bytes32 public challengeNumber;

uint public difficulty;

uint public tokensMinted;

uint public epochCount;

event Mint(address indexed from, uint rewardAmount, uint epochCount, bytes32 newChallengeNumber);

function mint(uint256 nonce) public returns (bool success);

function getAdjustmentInterval() public view returns (uint);

function getChallengeNumber() public view returns (bytes32);

function getMiningDifficulty() public view returns (uint);

function getMiningTarget() public view returns (uint);

function getMiningReward() public view returns (uint);

function decimals() public view returns (uint8);

contract AbstractERC918 is EIP918Interface {

    // the amount of time between difficulty adjustments
    uint public adjustmentInterval;
     
    // generate a new challenge number after a new reward is minted
    bytes32 public challengeNumber;
    
    // the current mining target
    uint public miningTarget;

    // cumulative counter of the total minted tokens
    uint public tokensMinted;

    // number of blocks per difficulty readjustment
    uint public blocksPerReadjustment;

    //number of 'blocks' mined
    uint public epochCount;
   
    /*
     * Externally facing mint function that is called by miners to validate challenge digests, calculate reward,
     * populate statistics, mutate epoch variables and adjust the solution difficulty as required. Once complete,
     * a Mint event is emitted before returning a success indicator.
     **/
    function mint(uint256 nonce) public returns (bool success) {
        require(msg.sender != address(0));

        // perform the hash function validation
        hash(nonce);
        
        // calculate the current reward
        uint rewardAmount = _reward();
        
        // increment the minted tokens amount
        tokensMinted += rewardAmount;
        
        epochCount = _epoch();

        //every so often, readjust difficulty. Don't readjust when deploying
        if(epochCount % blocksPerReadjustment == 0){
            _adjustDifficulty();
        }
       
        // send Mint event indicating a successful implementation
        emit Mint(msg.sender, rewardAmount, epochCount, challengeNumber);
        
        return true;
    }
}

uint public adjustmentInterval;

bytes32 public challengeNumber;

uint public miningTarget;

uint public tokensMinted;

uint public blocksPerReadjustment;

uint public epochCount;

event Mint(address indexed from, uint reward_amount, uint epochCount, bytes32 newChallengeNumber);

function mint(uint256 nonce) public returns (bool success);

function hash(uint256 nonce) public returns (bytes32 digest);

function _reward() internal returns (uint);

function _newEpoch(uint256 nonce) internal returns (uint);

function _adjustDifficulty() internal returns (uint);

function getAdjustmentInterval() public view returns (uint);

function getChallengeNumber() public view returns (bytes32);

function getMiningDifficulty() public view returns (uint);

function getMiningReward() public view returns (uint);

/**
 * @title ERC-918 Mineable Token Standard, optional merged mining functionality
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-918.md
 * 
 */
contract ERC918Merged is AbstractERC918 {
    /*
     * @notice Externally facing merge function that is called by miners to validate challenge digests, calculate reward,
     * populate statistics, mutate state variables and adjust the solution difficulty as required. Additionally, the
     * merge function takes an array of target token addresses to be used in merged rewards. Once complete,
     * a Mint event is emitted before returning a success indicator.
     *
     * @param _nonce the solution nonce
     **/
    function merge(uint256 _nonce, address[] _mineTokens) public returns (bool) {
      for (uint i = 0; i < _mineTokens.length; i++) {
        address tokenAddress = _mineTokens[i];
        ERC918Interface(tokenAddress).mint(_nonce);
      }
    }

    /*
     * @notice Externally facing merge function kept for backwards compatibility with previous definition
     *
     * @param _nonce the solution nonce
     * @param _challenge_digest the keccak256 encoded challenge number + message sender + solution nonce
     **/
     function merge(uint256 _nonce, bytes32 _challenge_digest, address[] _mineTokens) public returns (bool) {
       //the challenge digest must match the expected
       bytes32 digest = keccak256( abi.encodePacked(challengeNumber, msg.sender, _nonce) );
       require(digest == _challenge_digest, "Challenge digest does not match expected digest on token contract [ ERC918Merged.mint() ]");
       return merge(_nonce, _mineTokens);
     }
}

function merge(uint256 _nonce, address[] _mineTokens) public returns (bool)

function merge(uint256 _nonce, bytes32 _challenge_digest, address[] _mineTokens) public returns (bool)

import 'openzeppelin-solidity/contracts/contracts/cryptography/ECDSA.sol';

contract ERC918DelegatedMint is AbstractERC918, ECDSA {
   /**
     * @notice Hash (keccak256) of the payload used by delegatedMint
     * @param _nonce the golden nonce
     * @param _origin the original minter
     * @param _signature the original minter's elliptical curve signature
     */
    function delegatedMint(uint256 _nonce, address _origin, bytes _signature) public returns (bool success) {
        bytes32 hashedTx = delegatedMintHashing(_nonce, _origin);
        address minter = recover(hashedTx, _signature);
        require(minter == _origin, "Origin minter address does not match recovered signature address [ AbstractERC918.delegatedMint() ]");
        require(minter != address(0), "Invalid minter address recovered from signature [ ERC918DelegatedMint.delegatedMint() ]");
        success = mintInternal(_nonce, minter);
    }

    /**
     * @notice Hash (keccak256) of the payload used by delegatedMint
     * @param _nonce the golden nonce
     * @param _origin the original minter
     */
    function delegatedMintHashing(uint256 _nonce, address _origin) public pure returns (bytes32) {
        /* "0x7b36737a": delegatedMintHashing(uint256,address) */
        return toEthSignedMessageHash(keccak256(abi.encodePacked( bytes4(0x7b36737a), _nonce, _origin)));
    }
}

function delegatedMint(uint256 _nonce, address _origin, bytes _signature) public returns (bool success)

function delegatedMintHashing(uint256 _nonce, address _origin) public pure returns (bytes32)

{
  "nonce": "string",
  "origin": "string",
  "signature": "string"
}

/**
 * @title ERC-918 Mineable Token Standard, optional metadata extension
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-918.md
 * 
 */
interface ERC918Metadata is AbstractERC918 {
    /**
     * @notice A distinct Uniform Resource Identifier (URI) for a mineable asset.
     */
    function metadataURI() external view returns (string);
}

function metadataURI() external view returns (string);

{
    "title": "Mineable Token Metadata",
    "type": "object",
    "properties": {
        "symbol": {
            "type": "string",
            "description": "Identifies the Mineable Token's symbol",
        },
        "name": {
            "type": "string",
            "description": "Identifies the Mineable Token's name",
        },
        "description": {
            "type": "string",
            "description": "Identifies the Mineable Token's long description",
        },
        "website": {
            "type": "string",
            "description": "Identifies the Mineable Token's homepage URI",
        },
        "image": {
            "type": "string",
            "description": "Identifies the Mineable Token's image URI",
        },
        "type": {
            "type": "string",
            "description": "Identifies the Mineable Token's hash algorithm ( ie.keccak256 ) used to encode the solution",
        }
    }
}

/**
 * @title ERC-918 Mineable Token Standard, optional backwards compatibility function
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-918.md
 * 
 */
contract ERC918BackwardsCompatible is AbstractERC918 {

    /*
     * @notice Externally facing mint function kept for backwards compatibility with previous mint() definition
     * @param _nonce the solution nonce
     * @param _challenge_digest the keccak256 encoded challenge number + message sender + solution nonce
     **/
    function mint(uint256 _nonce, bytes32 _challenge_digest) public returns (bool success) {
        //the challenge digest must match the expected
        bytes32 digest = keccak256( abi.encodePacked(challengeNumber, msg.sender, _nonce) );
        require(digest == _challenge_digest, "Challenge digest does not match expected digest on token contract [ AbstractERC918.mint() ]");
        success = mint(_nonce);
    }
}