EIP 1014: Skinny CREATE2 Source

AuthorVitalik Buterin
StatusDraft
TypeStandards Track
CategoryCore
Created2018-04-20

Specification

Adds a new opcode at 0xf5, which takes 4 stack arguments: endowment, memory_start, memory_length, salt. Behaves identically to CREATE, except using keccak256( 0xff ++ address ++ salt ++ keccak256(init_code)))[12:] instead of the usual sender-and-nonce-hash as the address where the contract is initialized at.

The CREATE2 has the same gas 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 gas and CreateGas is deducted: before evaluation of the resulting address and the execution of init_code.

  • 0xff is a single byte,
  • address is always 20 bytes,
  • salt is always 32 bytes (a stack item).

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

The coredev-call at 2018-08-10 decided to use the formula above.

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.

Rationale

Address formula

  • Ensures that addresses created with this scheme cannot collide with addresses created using the traditional keccak256(rlp([sender, nonce])) formula, as 0xff can only be a starting byte for RLP for data many petabytes long.
  • Ensures that the hash preimage has a fixed size,

Gas 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 EIP uses the same cost-per-word as the SHA3 opcode.

Clarifications

The init_code is the code that, when executed, produces the runtime bytecode that will be placed into the state, and which typically is used by high level languages to implement a ‘constructor’.

This EIP makes collisions possible. The behaviour at collisions is specified by EIP 684:

If a contract creation is attempted, due to either a creation transaction or the CREATE (or future CREATE2) opcode, and the destination address already has either nonzero nonce, or nonempty code, then the creation throws immediately, with exactly the same behavior as would arise if the first byte in the init code were an invalid opcode. This applies retroactively starting from genesis.

Specifically, if nonce or code is nonzero, then the create-operation fails.

With EIP 161

Account creation transactions and the CREATE operation SHALL, prior to the execution of the initialisation code, increment the nonce over and above its normal starting value by one

This means that if a contract is created in a transaction, the nonce is immediately non-zero, with the side-effect that a collision within the same transaction will always fail – even if it’s carried out from the init_code itself/

It should also be noted that SELFDESTRUCT has no immediate effect on nonce or code, thus a contract cannot be destroyed and recreated within one transaction.

Examples

Example 0

  • address 0x0000000000000000000000000000000000000000
  • salt 0x0000000000000000000000000000000000000000000000000000000000000000
  • init_code 0x00
  • gas (assuming no mem expansion): 32006
  • result: 0x4D1A2e2bB4F88F0250f26Ffff098B0b30B26BF38

Example 1

  • address 0xdeadbeef00000000000000000000000000000000
  • salt 0x0000000000000000000000000000000000000000000000000000000000000000
  • init_code 0x00
  • gas (assuming no mem expansion): 32006
  • result: 0xB928f69Bb1D91Cd65274e3c79d8986362984fDA3

Example 2

  • address 0xdeadbeef00000000000000000000000000000000
  • salt 0x000000000000000000000000feed000000000000000000000000000000000000
  • init_code 0x00
  • gas (assuming no mem expansion): 32006
  • result: 0xD04116cDd17beBE565EB2422F2497E06cC1C9833

Example 3

  • address 0x0000000000000000000000000000000000000000
  • salt 0x0000000000000000000000000000000000000000000000000000000000000000
  • init_code 0xdeadbeef
  • gas (assuming no mem expansion): 32006
  • result: 0x70f2b2914A2a4b783FaEFb75f459A580616Fcb5e

Example 4

  • address 0x00000000000000000000000000000000deadbeef
  • salt 0x00000000000000000000000000000000000000000000000000000000cafebabe
  • init_code 0xdeadbeef
  • gas (assuming no mem expansion): 32006
  • result: 0x60f3f640a8508fC6a86d45DF051962668E1e8AC7

Example 5

  • address 0x00000000000000000000000000000000deadbeef
  • salt 0x00000000000000000000000000000000000000000000000000000000cafebabe
  • init_code 0xdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef
  • gas (assuming no mem expansion): 32012
  • result: 0x1d8bfDC5D46DC4f61D6b6115972536eBE6A8854C

Example 6

  • address 0x0000000000000000000000000000000000000000
  • salt 0x0000000000000000000000000000000000000000000000000000000000000000
  • init_code 0x
  • gas (assuming no mem expansion): 32000
  • result: 0xE33C0C7F7df4809055C3ebA6c09CFe4BaF1BD9e0