diff --git a/channel.sol b/channel.sol
index 8bdb7f6..d8e56ba 100644
--- a/channel.sol
+++ b/channel.sol
@@ -1,51 +1,58 @@
-pragma solidity ^0.4.0;
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
 
 contract Channel {
-
-	address public channelSender;
-	address public channelRecipient;
-	uint public startDate;
-	uint public channelTimeout;
-	mapping (bytes32 => address) signatures;
-
-	function Channel(address to, uint timeout) payable {
-		channelRecipient = to;
-		channelSender = msg.sender;
-		startDate = now;
-		channelTimeout = timeout;
-	}
-
-	function CloseChannel(bytes32 h, uint8 v, bytes32 r, bytes32 s, uint value){
-
-		address signer;
-		bytes32 proof;
-
-		// get signer from signature
-		signer = ecrecover(h, v, r, s);
-
-		// signature is invalid, throw
-		if (signer != channelSender && signer != channelRecipient) throw;
-
-		proof = sha3(this, value);
-
-		// signature is valid but doesn't match the data provided
-		if (proof != h) throw;
-
-		if (signatures[proof] == 0)
-			signatures[proof] = signer;
-		else if (signatures[proof] != signer){
-			// channel completed, both signatures provided
-			if (!channelRecipient.send(value)) throw;
-			selfdestruct(channelSender);
-		}
-
-	}
-
-	function ChannelTimeout(){
-		if (startDate + channelTimeout > now)
-			throw;
-
-		selfdestruct(channelSender);
-	}
-
+    address public channelSender;
+    address public channelRecipient;
+    uint public startDate;
+    uint public channelDuration;
+    uint public channelMargin;
+    bytes32 public channelTip;
+    bool public isActive;
+
+    constructor(address to, uint timeout, uint margin, bytes32 tip) payable {
+        channelRecipient = to;
+        channelSender = msg.sender;
+        startDate = block.timestamp;
+        channelDuration = timeout;
+        channelMargin = margin;
+        channelTip = tip;
+        isActive = true;
+    }
+
+    modifier onlyActive() {
+        require(isActive, "Channel is not active.");
+        _;
+    }
+
+    function closeChannel(bytes32 _word, uint8 _wordCount) public onlyActive {
+        require(msg.sender == channelRecipient, "Only the recipient can close the channel.");
+        bytes32 wordScratch = _word;
+        for (uint i = 1; i <= _wordCount; i++) {
+            wordScratch = keccak256(abi.encodePacked(wordScratch));
+        }
+
+        require(wordScratch == channelTip, "Invalid word or word count.");
+        (bool sent, ) = channelRecipient.call{value: _wordCount * channelMargin}("");
+        require(sent, "Failed to send Ether");
+        deactivate();
+    }
+
+    function expireChannel() public onlyActive {
+        require(block.timestamp >= startDate + channelDuration, "Channel timeout has not been reached.");
+        deactivate();
+    }
+
+    function deactivate() private {
+        isActive = false;
+        uint balance = address(this).balance;
+        if (balance > 0) {
+            (bool sent, ) = channelSender.call{value: balance}("");
+            require(sent, "Failed to return remaining Ether to sender");
+        }
+    }
+
+    receive() external payable {}
+
+    fallback() external payable {}
 }