Do you know the offset of a parameter in the external function’s calldata area? In order to extract a parameter from the calldata area directly, you have to know the offset. It requires you to know about the layout of calldata.Calldata is a non-modifiable, non-persistent area where function arguments are stored, and behaves mostly like memory.In other words, ABI encoded function data exists in there.What is the rule to encode though?Contract ABI stands for: The Contract Application Binary Interface (ABI) is the standard way to interact with contracts in the Ethereum ecosystem, both from outside the blockchain and for contract-to-contract interaction. Data is encoded according to its type, as described in this specification. The encoding is not self describing and thus requires a schema in order to decode. We assume the interface functions of a contract are strongly typed, known at compilation time and static. We assume that all contracts will have the interface definitions of any contracts they call available at compile-time. You can understand the encoding rule of function parameters and use this knowledge to get the correct data offset you want to get in calldata.Here is a good Solidity wargame inspired by Ethernaut.Through that, you can practice calldata […]