Smart Contract Safety: Best Practices & Design Patterns

Blockchain technology is still a highly experimental technology. Things move fast and you should expect constant changes in the security landscape, as new bugs and security risks are discovered and new best practices are developed. Following the security practices described in this article will help you better understand how to design flawless Ethereum smart contracts.

Developing with a security mindset is extremely important as the cost of failure can be high and change can be difficult. A basic defence mechanism against known vulnerabilities is therefore not enough. It’s recommended to use secure design patterns like rate limiters, exit strategies or circuit breakers to protect your contract against unexpected events.

Prepare For Failure

Any non-trivial contract will have errors in it. Your code must, therefore, be able to respond to bugs and vulnerabilities gracefully. When writing code, bear in mind the following security design patterns.

Checks-Effects-Interaction Pattern

This is the general guideline when coding any smart contract as it describes how to build up a function. You start with validating all the arguments and throwing appropriate errors when the args do not apply with the expected input. Next, you can make changes to the smart contract’s state and finally interact with other smart contracts.

Interacting with other contracts should always be the last step in your function as this mostly includes handing over the control to another contract. So, when we are handing over the control, it’s crucial that the current contract has finished its functionality and does not depend on the execution of the other contract. Here’s an example that comes from an Auction contract to set the end of the auction using a boolean.

Circuit Breaker

A circuit breaker, also referred to as an emergency stop, is capable of stopping the execution of functions inside the smart contract. A circuit breaker can be triggered manually by trusted parties included in the contract like the contract admin or by using programmatic rules that automatically trigger the circuit breaker when the defined conditions are met. The most common usage of a circuit breaker is when a bug is discovered.

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