Phase 0 -- Deposit Contract¶

Introduction
Constants
Configuration
Staking deposit contract
deposit function
Solidity code

Introduction¶

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

Constants¶

The following values are (non-configurable) constants used throughout the specification.

Name	Value
`DEPOSIT_CONTRACT_TREE_DEPTH`	`2**5` (= 32)

Configuration¶

Note: The default mainnet configuration values are included here for spec-design purposes. The different configurations for mainnet, testnets, and YAML-based testing can be found in the configs/constant_presets directory. These configurations are updated for releases and may be out of sync during dev changes.

Name	Value
`DEPOSIT_CHAIN_ID`	`1`
`DEPOSIT_NETWORK_ID`	`1`
`DEPOSIT_CONTRACT_ADDRESS`	`0x00000000219ab540356cBB839Cbe05303d7705Fa`

Staking deposit contract¶

The initial deployment phases of Ethereum proof-of-stake are implemented without consensus changes to the existing Ethereum proof-of-work chain. A deposit contract at address DEPOSIT_CONTRACT_ADDRESS is added to the Ethereum proof-of-work chain defined by the chain-id -- DEPOSIT_CHAIN_ID -- and the network-id -- DEPOSIT_NETWORK_ID -- for deposits of ETH to the beacon chain. Validator balances will be withdrawable to the execution-layer in a followup fork after Bellatrix upgrade.

Note: See here for a comprehensive list of public Ethereum chain chain-id's and network-id's.

`deposit` function¶

The deposit contract has a public deposit function to make deposits. It takes as arguments bytes calldata pubkey, bytes calldata withdrawal_credentials, bytes calldata signature, bytes32 deposit_data_root. The first three arguments populate a DepositData object, and deposit_data_root is the expected DepositData root as a protection against malformed calldata.

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 the execution-layer until sometime after Bellatrix upgrade.

Withdrawal credentials¶

One of the DepositData fields is withdrawal_credentials which constrains validator withdrawals. The first byte of this 32-byte field is a withdrawal prefix which defines the semantics of the remaining 31 bytes. The withdrawal prefixes currently supported are BLS_WITHDRAWAL_PREFIX and ETH1_ADDRESS_WITHDRAWAL_PREFIX. Read more in the validator guide.

Note: The deposit contract does not validate the withdrawal_credentials field. Support for new withdrawal prefixes can be added without modifying the deposit contract.

`DepositEvent` log¶

Every 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.

Solidity code¶

The deposit contract source code, written in Solidity, 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.