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
    • Gwei values
    • Contract
  • Ethereum 1.0 deposit contract
    • Arguments
      • Withdrawal credentials
      • Amount
  • Event logs
    • Deposit logs
    • Eth2Genesis log
  • Vyper code

Introduction

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

Constants

Gwei values

Name	Value	Unit
FULL_DEPOSIT_AMOUNT	32 * 10**9	Gwei

Contract

Name	Value
DEPOSIT_CONTRACT_ADDRESS	TBD
DEPOSIT_CONTRACT_TREE_DEPTH	2**5 (= 32)
CHAIN_START_FULL_DEPOSIT_THRESHOLD	2**16 (= 65,536)

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).

Arguments

The deposit contract has a deposit function which takes the amount in Ethereum 1.0 transaction, and arguments pubkey: bytes[48], withdrawal_credentials: bytes[32], signature: bytes[96] corresponding to DepositData.

Withdrawal credentials

One of the DepositData fields is withdrawal_credentials. It is a commitment to credentials for withdrawals 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.

Amount

• A valid deposit amount should be at least MIN_DEPOSIT_AMOUNT in Gwei.
• A deposit with an amount greater than or equal to FULL_DEPOSIT_AMOUNT in Gwei is considered as a full deposit.

Event logs

Deposit logs

Every Ethereum 1.0 deposit, of size at least MIN_DEPOSIT_AMOUNT, emits a Deposit 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.

Eth2Genesis log

When CHAIN_START_FULL_DEPOSIT_THRESHOLD of full deposits have been made, the deposit contract emits the Eth2Genesis log. The beacon chain state may then be initialized by calling the get_genesis_beacon_state function (defined here) where:

• genesis_time equals time in the Eth2Genesis log
• latest_eth1_data.deposit_root equals deposit_root in the Eth2Genesis log
• latest_eth1_data.deposit_count equals deposit_count in the Eth2Genesis log
• latest_eth1_data.block_hash equals the hash of the block that included the log
• genesis_validator_deposits is a list of Deposit objects built according to the Deposit logs up to the deposit that triggered the Eth2Genesis log, processed in the order in which they were emitted (oldest to newest)

Vyper code

The source for the Vyper contract lives here.

Note: To save ~10x on gas, this contract uses a somewhat unintuitive progressive Merkle root calculation algo that requires only O(log(n)) storage. See https://github.com/ethereum/research/blob/master/beacon_chain_impl/progressive_merkle_tree.py for an implementation of the same algo in Python tested for correctness.

For convenience, we provide the interface to the contract here:

• __init__(): initializes the contract
• get_deposit_root() -> bytes32: returns the current root of the deposit tree
• deposit(pubkey: bytes[48], withdrawal_credentials: bytes[32], signature: bytes[96]): adds a deposit instance to the deposit tree, incorporating the input arguments and the value transferred in the given call. Note: The amount of value transferred must be at least MIN_DEPOSIT_AMOUNT. Each of these constants are specified in units of Gwei.