Introduction

Ethereum precompiles behave like smart contracts built into the Ethereum protocol. These operations are desirable enough to have gas-efficient mechanism for doing them. Implementing these algorithms in Solidity would be considerably less gas efficient.

The idea was that led to precompiles was solving the problem of allowing complex cryptographic computations to be usable in the EVM without having to deal with EVM overhead.

The utility of precompiles falls into four categories

• Elliptic curve digital signature recovery
• Hash methods to interact with bitcoin and zcash
• Memory copying
• Methods to enable elliptic curve math for zero knowledge proofs

Precompiles do not execute inside a smart contract (they are not EVM bytecode), they are part of the Ethereum execution client specification.

Call Precompiled Smart Contracts with Solidity

Most precompiles don’t have a solidity wrapper (with ecrecover being the sole exception). You’ll need to call the address directly with addressOfPrecompile.staticcall(…) or use assembly.

Example:

function recoverSignature(bytes32 hash, uint8 v, bytes32 r, bytes32 s) public view returns (address) {
        address r = ecrecover(hash, v, r, s);
        require(r != address(0), "signature is invalid");
}

Complete List of Precompiles

This is the snippet of code directly from Geth (go-ethereum), the most famous Ethereum execution client, developed by the Ethereum Foundation.

// PrecompiledContractsCancun contains the default set of pre-compiled Ethereum
// contracts used in the Cancun release.
var PrecompiledContractsCancun = map[common.Address]PrecompiledContract{
	common.BytesToAddress([]byte{1}):  &ecrecover{},
	common.BytesToAddress([]byte{2}):  &sha256hash{},
	common.BytesToAddress([]byte{3}):  &ripemd160hash{},
	common.BytesToAddress([]byte{4}):  &dataCopy{},
	common.BytesToAddress([]byte{5}):  &bigModExp{eip2565: true},
	common.BytesToAddress([]byte{6}):  &bn256AddIstanbul{},
	common.BytesToAddress([]byte{7}):  &bn256ScalarMulIstanbul{},
	common.BytesToAddress([]byte{8}):  &bn256PairingIstanbul{},
	common.BytesToAddress([]byte{9}):  &blake2F{},
	common.BytesToAddress([]byte{20}): &kzgPointEvaluation{},
}

You can already see the newest precompile kzgPointEvaluation that is going to be added in the Cancun release.

Implementation

As you can read from the comments, a precompile contract just needs to implement the PrecompiledContract interface (speaking of Geth).