Mastering Blockchain Programming with Solidity

Cryptographic functions

Cryptographic functions can be used in contracts to calculate the sha256 and keccak256 hashes. The ecrecover function is used to verify that the hashes are signed by a specific address's private key:

• keccak256(bytes memory) returns (bytes32): This is also called Ethereum SHA3. This computes the Ethereum-SHA-3 (Keccak-256) hash of the tightly packed arguments and returns it as bytes32.
• sha256(bytes memory) returns (bytes32): This computes the SHA-256 hash of the input bytes and returns it as bytes32.
• ecrecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) returns (address): Recovers the address associated with the public key from an elliptic curve signature or returns 0 on error.

When using ecrecover always check for ...