eth2.0-specs/specs/core/0_deposit-contract.md

Ethereum 2.0 Phase 0 -- Deposit Contract

Notice: This document is a work-in-progress for researchers and implementers.

Table of contents

• Ethereum 2.0 Phase 0 -- Deposit Contract
  • Table of contents
  • Introduction
  • Constants
    • Contract
  • Ethereum 1.0 deposit contract
    • deposit function
      • Deposit amount
      • Withdrawal credentials
      • DepositEvent log
  • Vyper code

Introduction

This document represents the specification for the beacon chain deposit contract, part of Ethereum 2.0 Phase 0.

Constants

Contract

Name	Value
DEPOSIT_CONTRACT_ADDRESS	TBD
DEPOSIT_CONTRACT_TREE_DEPTH	2**5 (= 32)

Ethereum 1.0 deposit contract

The initial deployment phases of Ethereum 2.0 are implemented without consensus changes to Ethereum 1.0. A deposit contract at address DEPOSIT_CONTRACT_ADDRESS is added to Ethereum 1.0 for deposits of ETH to the beacon chain. Validator balances will be withdrawable to the shards in Phase 2 (i.e. when the EVM 2.0 is deployed and the shards have state).

deposit function

The deposit contract has a public deposit function to make deposits. It takes as arguments pubkey: bytes[48], withdrawal_credentials: bytes[32], signature: bytes[96] corresponding to a DepositData object.

Deposit amount

The amount of ETH (rounded down to the closest Gwei) sent to the deposit contract is the deposit amount, which must be of size at least MIN_DEPOSIT_AMOUNT Gwei. Note that ETH consumed by the deposit contract is no longer usable on Ethereum 1.0.

Withdrawal credentials

One of the DepositData fields is withdrawal_credentials. It is a commitment to credentials for withdrawing validator balance (e.g. to another validator, or to shards). The first byte of withdrawal_credentials is a version number. As of now, the only expected format is as follows:

• withdrawal_credentials[:1] == BLS_WITHDRAWAL_PREFIX_BYTE
• withdrawal_credentials[1:] == hash(withdrawal_pubkey)[1:] where withdrawal_pubkey is a BLS pubkey

The private key corresponding to withdrawal_pubkey will be required to initiate a withdrawal. It can be stored separately until a withdrawal is required, e.g. in cold storage.

DepositEvent log

Every Ethereum 1.0 deposit emits a DepositEvent log for consumption by the beacon chain. The deposit contract does little validation, pushing most of the validator onboarding logic to the beacon chain. In particular, the proof of possession (a BLS12-381 signature) is not verified by the deposit contract.

Vyper code

The deposit contract source code, written in Vyper, is available here.

Note: To save on gas, the deposit contract uses a progressive Merkle root calculation algorithm that requires only O(log(n)) storage. See here for a Python implementation, and here for a formal correctness proof.