Securing the Future of Smart Contracts

Securing the Future of Smart Contracts: EU Legislation Mandates Kill Switch Implementation

In a recent move aimed at increasing the security and control of smart contracts, the European Parliament has passed legislation requiring all smart contracts to include a kill switch. This development has sparked much debate and discussion within the blockchain and cryptocurrency communities.

Who passed the bill, when, and for what purpose?

The European Parliament passed the bill on March 10th, 2023, with the purpose of enhancing the security and stability of blockchain-based applications and digital assets. The lawmakers believe that this measure will protect users from potential exploitation by hackers or malicious actors while also providing a regulatory safeguard in case of unforeseen issues or disputes involving smart contracts.

“The smart contract shall include internal functions which can reset or instruct the contract to stop or interrupt the operation. […] Especially, it should be assessed under which conditions non-consensual termination or interruption should be permissible.”

The act also granted smart contracts equal protection when compared with other forms of contract.

“Including a kill switch undermines immutability guarantees and introduces a point of failure since someone needs to govern the use of such a kill switch. […] Many smart contracts such as Uniswap do not have this kill switch ability.”

The bill was passed by a margin of 500-23, with 110 abstentions. Parliament members will now negotiate the final form of the law with the European Council and individual member countries of the European Union.

What exactly is a kill switch and what code needs to be implemented?

A kill switch is a built-in mechanism that allows for the termination or suspension of a smart contract under specific conditions. This can be particularly useful in cases where a contract has been compromised, or if there is a need to halt its execution due to unforeseen circumstances or legal disputes.

To comply with the new legislation, developers will need to incorporate a kill switch into their smart contract code. This may include a combination of access controls, emergency stop functions, and time-locked actions that can be triggered by designated parties or under specific conditions. The exact implementation may vary depending on the blockchain platform and the nature of the smart contract.

Smart contract kill switch is simply a built-in mechanism within a smart contract that allows for its termination or suspension under specific conditions. This feature is designed to enhance the security and control of smart contracts by providing a way to halt their execution in case of unforeseen issues, disputes, or potential exploitation by hackers or malicious actors. The kill switch can be triggered by designated parties or under certain pre-defined conditions, depending on its implementation within the smart contract code.

In a Solidity smart contract, a kill switch can be implemented using a combination of modifiers, functions, and access controls. Here’s an example of how to implement a basic kill switch in a Solidity smart contract

pragma solidity ^0.8.0;
contract KillSwitchExample {
  address public owner;
  bool public isPaused;
  // Set the contract's owner as the deployer of the contract
  constructor() {
      owner = msg.sender;
  // Modifier to check if the contract is paused
  modifier whenNotPaused() {
      require(!isPaused, "Contract is paused");
  // Modifier to check if the caller is the owner
  modifier onlyOwner() {
      require(msg.sender == owner, "Caller is not the owner");
  // Function to pause or unpause the contract
  function setPaused(bool _isPaused) public onlyOwner {
      isPaused = _isPaused;
  // Example function that can only be called when the contract is not paused
  function doSomething() public whenNotPaused {
      // Your function logic here

In this example, the kill switch is implemented using the isPaused state variable and the whenNotPaused modifier. The setPaused function allows the contract owner to pause or unpause the contract. When the contract is paused, any function using the whenNotPaused modifier will not be executed, effectively suspending the smart contract’s operation.

This is a simple example, and depending on the complexity of your smart contract, you may need to customize the kill switch implementation to suit your specific requirements.

Does the passage of this bill make it illegal to use previously deployed contracts without a kill switch?

The new legislation does not make it illegal to use previously deployed smart contracts that do not have a kill switch. However, it does require developers to update their existing smart contracts to include a kill switch if they want to continue using them within the European Union. Failure to comply with the legislation may result in penalties or other legal consequences for the developers and users of non-compliant smart contracts.

Will companies and individuals who develop contracts without kill switches no longer be able to provide services to users in the EU?

Following the passage of this bill, companies and individuals developing smart contracts without kill switches will not be able to offer their services to users within the European Union. To continue providing services, they will need to ensure that their smart contracts are compliant with the new legislation. This may require making updates to their code, auditing their smart contracts for potential vulnerabilities, and seeking legal advice to ensure they are operating within the bounds of the new regulation.


In conclusion, the European Parliament’s legislation requiring smart contracts to include a kill switch is a significant development in the realm of blockchain technology and digital assets. While it may pose some challenges for developers and businesses, it also has the potential to increase the overall security and stability of smart contracts, providing greater protection for users and a safer environment for the growth of blockchain-based applications in the EU.

Share this article: