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Simple Summary

A new contract creation function called CREATE2.

Abstract

A new method of creating a contract is proposed where the resulting address can be determined by parties ahead of time.

Motivation

Allows interactions to (actually or counterfactually in channels) be made with addresses that do not exist yet on-chain but can be relied on to only possibly eventually contain code that has been created by a particular piece of init code. Important for state-channel use cases that involve counterfactual interactions with contracts.

Specification

Adds a new opcode at 0xf5, which takes 4 stack arguments: endowment, memory_start, memory_length, salt. Behaves identically to CREATE, except using addressPrefix ++ keccak256(address ++ salt ++ keccak256(init_code))[12:] to create a new contract address. addressPrefix is 0x41 forT The CREATE2 has the same engery schema as CREATE, but also an extra hashcost of GSHA3WORD * ceil(len(init_code) / 32), to account for the hashing that must be performed. The hashcost is deducted at the same time as memory-expansion engery and Create is deducted: before evaluation of the resulting address and the execution of ``.

  • address is always 21 bytes,
  • salt is always 32 bytes (a stack item).
  • keccak256(init_code) 32 bytes

The preimage for the final hashing round is thus always exactly 85 bytes long.

Rationale

Address formula

  • Because instruction CREATE mainly depends on trxHash, the CREATE2 addresses will not collide with CREATE addresses.
    • Deploy contract: addressPrefix ++ keccak256(trxHash ++ txOwnerAddress)[12:]
    • in internal transaction: addressPrefix ++ keccak256(trxHash ++ nonce)[12:]
  • Ensures that the hash preimage has a fixed size,

Engery cost Since address calculation depends on hashing the init_code, it would leave clients open to DoS attacks if executions could repeatedly cause hashing of large pieces of init_code, since expansion of memory is paid for only once. This TIP uses the same cost-per-word as the SHA3 opcode.