[Ethereum] How is the address of an Ethereum contract computed

addressescontract-deploymentcreatecreate2

How is the address of an Ethereum contract computed? What use cases are there for knowing a contract's address in advance?

Best Answer

EDIT April 2019: CREATE2 information added.

EDIT January 2022: Updated Solidity syntax to ^0.8.0.

The address for an Ethereum contract is deterministically computed from the address of its creator (sender) and how many transactions the creator has sent (nonce). The sender and nonce are RLP encoded and then hashed with Keccak-256.

From pyethereum:

def mk_contract_address(sender, nonce):
    return sha3(rlp.encode([normalize_address(sender), nonce]))[12:]

In Solidity:

nonce0= address(uint160(uint256(keccak256(abi.encodePacked(bytes1(0xd6), bytes1(0x94), _origin, bytes1(0x80))))));
nonce1= address(uint160(uint256(keccak256(abi.encodePacked(bytes1(0xd6), bytes1(0x94), _origin, bytes1(0x01))))));

Example with some discussion:

For sender 0x6ac7ea33f8831ea9dcc53393aaa88b25a785dbf0, the contract addresses that it will create are the following:

nonce0= "0xcd234a471b72ba2f1ccf0a70fcaba648a5eecd8d"
nonce1= "0x343c43a37d37dff08ae8c4a11544c718abb4fcf8"
nonce2= "0xf778b86fa74e846c4f0a1fbd1335fe81c00a0c91"
nonce3= "0xfffd933a0bc612844eaf0c6fe3e5b8e9b6c1d19c"

In Java with Web3j:

private String calculateContractAddress(String address, long nonce){
    byte[] addressAsBytes = Numeric.hexStringToByteArray(address);

    byte[] calculatedAddressAsBytes =
            Hash.sha3(RlpEncoder.encode(
                    new RlpList(
                            RlpString.create(addressAsBytes),
                            RlpString.create((nonce)))));

    calculatedAddressAsBytes = Arrays.copyOfRange(calculatedAddressAsBytes,
            12, calculatedAddressAsBytes.length);
    String calculatedAddressAsHex = Numeric.toHexString(calculatedAddressAsBytes);
    return calculatedAddressAsHex;
}

Note: As per EIP 161 A Specification contract accounts are initiated with nonce = 1 (in the mainnet). So the first contract address, created by another contract, will be computed with non-zero nonce.

CREATE2

A new opcode, CREATE2 was added in EIP-1014 that is another way that a contract can be created.

For contract created by CREATE2 its address will be:

keccak256( 0xff ++ senderAddress ++ salt ++ keccak256(init_code))[12:]

More information will be added here and for the meantime see EIP-1014.

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