diff --git a/contracts/GiftBucket.sol b/contracts/GiftBucket.sol
index db26803..d5834af 100644
--- a/contracts/GiftBucket.sol
+++ b/contracts/GiftBucket.sol
@@ -2,6 +2,7 @@ pragma solidity ^0.6.1;
 pragma experimental ABIEncoderV2;
 
 import "./erc20/IERC20.sol";
+import "./RedeemUtil.sol";
 
 contract GiftBucket {
 
@@ -23,17 +24,9 @@ contract GiftBucket {
 
   mapping(address => Gift) public gifts;
 
-  struct Redeem {
-    uint256 blockNumber;
-    bytes32 blockHash;
-    address receiver;
-    bytes32 code;
-  }
-
   uint256 public redeemableSupply;
 
   bytes32 constant EIP712DOMAIN_TYPEHASH = keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)");
-  bytes32 constant REDEEM_TYPEHASH = keccak256("Redeem(uint256 blockNumber,bytes32 blockHash,address receiver,bytes32 code)");
   bytes32 DOMAIN_SEPARATOR;
 
   modifier onlyOwner() {
@@ -48,7 +41,7 @@ contract GiftBucket {
   function initialize(address _tokenAddress, uint256 _expirationTime, address _owner) public {
     require(initialized == false, "already initialized");
 
-    require(_expirationTime > block.timestamp, "expiration can't be in the past");
+    RedeemUtil.validateExpiryDate(_expirationTime);
 
     tokenContract = IERC20(_tokenAddress);
     expirationTime = _expirationTime;
@@ -58,22 +51,13 @@ contract GiftBucket {
       EIP712DOMAIN_TYPEHASH,
       keccak256("KeycardGift"),
       keccak256("1"),
-      _getChainID(),
+      RedeemUtil.getChainID(),
       address(this)
     ));
 
     initialized = true;
   }
 
-  function _getChainID() internal pure returns (uint256) {
-    uint256 id;
-    assembly {
-      id := chainid()
-    }
-
-    return id;
-  }
-
   function totalSupply() public view returns(uint256) {
     return tokenContract.balanceOf(address(this));
   }
@@ -102,20 +86,15 @@ contract GiftBucket {
     redeemableSupply += amount;
   }
 
-  function redeem(Redeem calldata _redeem, bytes calldata sig) external {
-    require(_redeem.blockNumber < block.number, "transaction cannot be in the future");
-    require(_redeem.blockNumber >= (block.number - maxTxDelayInBlocks), "transaction too old");
-    require(_redeem.blockHash == blockhash(_redeem.blockNumber), "invalid block hash");
+  function redeem(RedeemUtil.Redeem calldata _redeem, bytes calldata _sig) external {
+    RedeemUtil.validateRedeem(_redeem, maxTxDelayInBlocks, expirationTime, 0);
 
-    require(block.timestamp < expirationTime, "expired gift");
-
-    address recipient = recoverSigner(_redeem, sig);
+    address recipient = RedeemUtil.recoverSigner(DOMAIN_SEPARATOR, _redeem, _sig);
 
     Gift storage gift = gifts[recipient];
     require(gift.recipient == recipient, "not found");
 
-    bytes32 codeHash = keccak256(abi.encodePacked(_redeem.code));
-    require(codeHash == gift.code, "invalid code");
+    RedeemUtil.validateCode(_redeem, gift.code);
 
     uint256 amount = gift.amount;
     require(redeemableSupply >= amount, "not enough redeemable supply");
@@ -127,49 +106,11 @@ contract GiftBucket {
   }
 
   function kill() external onlyOwner {
-    require(block.timestamp >= expirationTime, "not expired yet");
+    RedeemUtil.validateExpired(expirationTime);
 
     bool success = tokenContract.transfer(owner, this.totalSupply());
     assert(success);
 
     selfdestruct(owner);
   }
-
-  function hashRedeem(Redeem memory _redeem) internal pure returns (bytes32) {
-    return keccak256(abi.encode(
-      REDEEM_TYPEHASH,
-      _redeem.blockNumber,
-      _redeem.blockHash,
-      _redeem.receiver,
-      _redeem.code
-    ));
-  }
-
-  function recoverSigner(Redeem memory _redeem, bytes memory sig) internal view returns(address) {
-    require(sig.length == 65, "bad signature length");
-
-    bytes32 r;
-    bytes32 s;
-    uint8 v;
-
-    assembly {
-      r := mload(add(sig, 32))
-      s := mload(add(sig, 64))
-      v := byte(0, mload(add(sig, 96)))
-    }
-
-    if (v < 27) {
-      v += 27;
-    }
-
-    require(v == 27 || v == 28, "signature version doesn't match");
-
-    bytes32 digest = keccak256(abi.encodePacked(
-        "\x19\x01",
-        DOMAIN_SEPARATOR,
-        hashRedeem(_redeem)
-    ));
-
-    return ecrecover(digest, v, r, s);
-  }
 }
diff --git a/contracts/NFTBucket.sol b/contracts/NFTBucket.sol
index 83bad7a..3a669a7 100644
--- a/contracts/NFTBucket.sol
+++ b/contracts/NFTBucket.sol
@@ -4,9 +4,9 @@ pragma experimental ABIEncoderV2;
 import "./erc721/IERC721.sol";
 import "./erc721/IERC721Receiver.sol";
 import "./erc721/IERC165.sol";
+import "./RedeemUtil.sol";
 
 contract NFTBucket is IERC165, IERC721Receiver {
-
   bool initialized;
 
   address payable public owner;
@@ -25,17 +25,9 @@ contract NFTBucket is IERC165, IERC721Receiver {
 
   mapping(address => Gift) public gifts;
 
-  struct Redeem {
-    uint256 blockNumber;
-    bytes32 blockHash;
-    address receiver;
-    bytes32 code;
-  }
-
   bytes4 private constant _ERC721_RECEIVED = 0x150b7a02; //bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))
 
   bytes32 constant EIP712DOMAIN_TYPEHASH = keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)");
-  bytes32 constant REDEEM_TYPEHASH = keccak256("Redeem(uint256 blockNumber,bytes32 blockHash,address receiver,bytes32 code)");
   bytes32 DOMAIN_SEPARATOR;
 
   modifier onlyOwner() {
@@ -50,7 +42,7 @@ contract NFTBucket is IERC165, IERC721Receiver {
   function initialize(address _tokenAddress, uint256 _expirationTime, address _owner) public {
     require(initialized == false, "already initialized");
 
-    require(_expirationTime > block.timestamp, "expiration can't be in the past");
+    RedeemUtil.validateExpiryDate(_expirationTime);
 
     tokenContract = IERC721(_tokenAddress);
     expirationTime = _expirationTime;
@@ -60,42 +52,28 @@ contract NFTBucket is IERC165, IERC721Receiver {
       EIP712DOMAIN_TYPEHASH,
       keccak256("KeycardNFTGift"),
       keccak256("1"),
-      _getChainID(),
+      RedeemUtil.getChainID(),
       address(this)
     ));
 
     initialized = true;
   }
 
-  function _getChainID() internal pure returns (uint256) {
-    uint256 id;
-    assembly {
-      id := chainid()
-    }
+  function redeem(RedeemUtil.Redeem calldata _redeem, bytes calldata _sig) external {
+    RedeemUtil.validateRedeem(_redeem, maxTxDelayInBlocks, expirationTime, 0);
 
-    return id;
-  }
-
-  function redeem(Redeem calldata _redeem, bytes calldata sig) external {
-    require(_redeem.blockNumber < block.number, "transaction cannot be in the future");
-    require(_redeem.blockNumber >= (block.number - maxTxDelayInBlocks), "transaction too old");
-    require(_redeem.blockHash == blockhash(_redeem.blockNumber), "invalid block hash");
-
-    require(block.timestamp < expirationTime, "expired gift");
-
-    address recipient = recoverSigner(_redeem, sig);
+    address recipient = RedeemUtil.recoverSigner(DOMAIN_SEPARATOR, _redeem, _sig);
 
     Gift storage gift = gifts[recipient];
     require(gift.recipient == recipient, "not found");
 
-    bytes32 codeHash = keccak256(abi.encodePacked(_redeem.code));
-    require(codeHash == gift.code, "invalid code");
+    RedeemUtil.validateCode(_redeem, gift.code);
 
     tokenContract.safeTransferFrom(address(this), _redeem.receiver, gift.tokenID);
   }
 
   function kill() external onlyOwner {
-    require(block.timestamp >= expirationTime, "not expired yet");
+    RedeemUtil.validateExpired(expirationTime);
 
     tokenContract.setApprovalForAll(owner, true);
     assert(tokenContract.isApprovedForAll(address(this), owner));
@@ -103,44 +81,6 @@ contract NFTBucket is IERC165, IERC721Receiver {
     selfdestruct(owner);
   }
 
-  function hashRedeem(Redeem memory _redeem) internal pure returns (bytes32) {
-    return keccak256(abi.encode(
-      REDEEM_TYPEHASH,
-      _redeem.blockNumber,
-      _redeem.blockHash,
-      _redeem.receiver,
-      _redeem.code
-    ));
-  }
-
-  function recoverSigner(Redeem memory _redeem, bytes memory sig) internal view returns(address) {
-    require(sig.length == 65, "bad signature length");
-
-    bytes32 r;
-    bytes32 s;
-    uint8 v;
-
-    assembly {
-      r := mload(add(sig, 32))
-      s := mload(add(sig, 64))
-      v := byte(0, mload(add(sig, 96)))
-    }
-
-    if (v < 27) {
-      v += 27;
-    }
-
-    require(v == 27 || v == 28, "signature version doesn't match");
-
-    bytes32 digest = keccak256(abi.encodePacked(
-        "\x19\x01",
-        DOMAIN_SEPARATOR,
-        hashRedeem(_redeem)
-    ));
-
-    return ecrecover(digest, v, r, s);
-  }
-
   function supportsInterface(bytes4 interfaceID) external override(IERC165) view returns (bool) {
       return interfaceID == _ERC721_RECEIVED;
   }
diff --git a/contracts/RedeemUtil.sol b/contracts/RedeemUtil.sol
new file mode 100644
index 0000000..980a9e6
--- /dev/null
+++ b/contracts/RedeemUtil.sol
@@ -0,0 +1,82 @@
+pragma solidity ^0.6.1;
+pragma experimental ABIEncoderV2;
+
+library RedeemUtil {
+  struct Redeem {
+    uint256 blockNumber;
+    bytes32 blockHash;
+    address receiver;
+    bytes32 code;
+  }
+
+  bytes32 constant REDEEM_TYPEHASH = keccak256("Redeem(uint256 blockNumber,bytes32 blockHash,address receiver,bytes32 code)");
+
+  function getChainID() internal pure returns (uint256) {
+    uint256 id;
+    assembly {
+      id := chainid()
+    }
+
+    return id;
+  }
+
+  function validateExpiryDate(uint256 _expirationTime) internal view {
+    require(_expirationTime > block.timestamp, "expiration can't be in the past");
+  }
+
+  function validateExpired(uint256 _expirationTime) internal view {
+    require(block.timestamp >= _expirationTime, "not expired yet");
+  }
+
+  function validateRedeem(Redeem memory _redeem, uint256 _maxTxDelayInBlocks, uint256 _expirationTime, uint256 _startTime) internal view {
+    require(_redeem.blockNumber < block.number, "transaction cannot be in the future");
+    require(_redeem.blockNumber >= (block.number - _maxTxDelayInBlocks), "transaction too old");
+    require(_redeem.blockHash == blockhash(_redeem.blockNumber), "invalid block hash");
+
+    require(block.timestamp < _expirationTime, "expired gift");     
+    require(block.timestamp > _startTime, "reedeming not yet started");     
+  }
+
+  function hashRedeem(Redeem memory _redeem) internal pure returns (bytes32) {
+    return keccak256(abi.encode(
+      REDEEM_TYPEHASH,
+      _redeem.blockNumber,
+      _redeem.blockHash,
+      _redeem.receiver,
+      _redeem.code
+    ));
+  }
+
+  function recoverSigner(bytes32 _domainSeparator, Redeem memory _redeem, bytes memory _sig) internal pure returns(address) {
+    require(_sig.length == 65, "bad signature length");
+
+    bytes32 r;
+    bytes32 s;
+    uint8 v;
+
+    assembly {
+      r := mload(add(_sig, 32))
+      s := mload(add(_sig, 64))
+      v := byte(0, mload(add(_sig, 96)))
+    }
+
+    if (v < 27) {
+      v += 27;
+    }
+
+    require(v == 27 || v == 28, "signature version doesn't match");
+
+    bytes32 digest = keccak256(abi.encodePacked(
+        "\x19\x01",
+        _domainSeparator,
+        hashRedeem(_redeem)
+    ));
+
+    return ecrecover(digest, v, r, s);
+  }
+
+  function validateCode(Redeem memory _redeem, bytes32 _code) internal pure {
+    bytes32 codeHash = keccak256(abi.encodePacked(_redeem.code));
+    require(codeHash == _code, "invalid code");
+  }
+}
\ No newline at end of file