Table of Contents for What is keccak256

Intro - what is Keccak256 and why is it used in Solidity

keccak256 is a very commonly used hash function in the Solidity programming language. It returns a bytes32 value.

It is based on SHA-3 (although is not technically the exact same).

Note: if you use the web3 JS library’s web3.utils.soliditySha3() function, you might be surprised to learn you are actually running keccak256, and not SHA3.

How to compare values with keccak256

You can pass in any number of arguments to keccak256. It is often used to check if two values are equal (by passing in values from abi.encodePacked(...)).

You can check if two values are the same but comparing the keccak256 value of them. For example:

isTheSame = keccak256(abi.encodePacked(someVariable)) == 
            keccak256(abi.encodePacked(anotherVariable));

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