Chapter 9. Smart Contract Security

Security is one of the most important considerations when writing smart contracts. In the field of smart contract programming, mistakes are costly and easily exploited. In this chapter we will look at security best practices and design patterns, as well as “security antipatterns,” which are practices and patterns that can introduce vulnerabilities in our smart contracts.

As with other programs, a smart contract will execute exactly what is written, which is not always what the programmer intended. Furthermore, all smart contracts are public, and any user can interact with them simply by creating a transaction. Any vulnerability can be exploited, and losses are almost always impossible to recover. It is therefore critical to follow best practices and use well-tested design patterns.

Security Best Practices

Defensive programming is a style of programming that is particularly well suited to smart contracts. It emphasizes the following, all of which are best practices:


Complexity is the enemy of security. The simpler the code, and the less it does, the lower the chances are of a bug or unforeseen effect occurring. When first engaging in smart contract programming, developers are often tempted to try to write a lot of code. Instead, you should look through your smart contract code and try to find ways to do less, with fewer lines of code, less complexity, and fewer “features.” If someone tells you that their project has produced ...

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