Merge pull request #995 from ethereum/deposit_contract_description

Modify deposit contract description

specs/core/0_deposit-contract.md

@@ -9,13 +9,16 @@
     - [Table of contents](#table-of-contents)
     - [Introduction](#introduction)
     - [Constants](#constants)
-        - [Deposit contract](#deposit-contract)
+        - [Gwei values](#gwei-values)
+        - [Contract](#contract)
     - [Ethereum 1.0 deposit contract](#ethereum-10-deposit-contract)
-        - [Deposit arguments](#deposit-arguments)
-        - [Withdrawal credentials](#withdrawal-credentials)
+        - [Arguments](#arguments)
+            - [Withdrawal credentials](#withdrawal-credentials)
+            - [Amount](#amount)
+    - [Event logs](#event-logs)
         - [`Deposit` logs](#deposit-logs)
         - [`Eth2Genesis` log](#eth2genesis-log)
-        - [Vyper code](#vyper-code)
+    - [Vyper code](#vyper-code)
 
 <!-- /TOC -->
 
@@ -25,22 +28,29 @@ This document represents is the specification for the beacon chain deposit contr
 
 ## Constants
 
-### Deposit contract
+### 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 EVM2.0 is deployed and the shards have state.
 
-### Deposit arguments
+### Arguments
 
-The deposit contract has a single `deposit` function which takes as argument a SimpleSerialize'd `DepositData`.
+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
+#### 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:
 
@@ -49,13 +59,20 @@ One of the `DepositData` fields is `withdrawal_credentials`. It is a commitment
 
 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 between `MIN_DEPOSIT_AMOUNT` and `MAX_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 signature) is not verified by the deposit contract.
+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 a sufficient amount 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 below) where:
+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 below) where:
 
 * `genesis_time` equals `time` in the `Eth2Genesis` log
 * `latest_eth1_data.deposit_root` equals `deposit_root` in the `Eth2Genesis` log
@@ -63,7 +80,7 @@ When a sufficient amount of full deposits have been made, the deposit contract e
 * `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
+## Vyper code
 
 The source for the Vyper contract lives in a [separate repository](https://github.com/ethereum/deposit_contract) at [https://github.com/ethereum/deposit_contract/blob/master/deposit_contract/contracts/validator_registration.v.py](https://github.com/ethereum/deposit_contract/blob/master/deposit_contract/contracts/validator_registration.v.py).
 
@@ -73,4 +90,4 @@ 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(bytes[512])`: adds a deposit instance to the deposit tree, incorporating the input argument and the value transferred in the given call. Note: the amount of value transferred *must* be within `MIN_DEPOSIT_AMOUNT` and `MAX_DEPOSIT_AMOUNT`, inclusive. Each of these constants are specified in units of Gwei.
+* `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.