0x02 Credential Prefix

specs/phase0/beacon-chain.md

@@ -192,6 +192,7 @@ The following values are (non-configurable) constants used throughout the specif
 | - | - |
 | `BLS_WITHDRAWAL_PREFIX` | `Bytes1('0x00')` |
 | `ETH1_ADDRESS_WITHDRAWAL_PREFIX` | `Bytes1('0x01')` |
+| `ETH1_ADDRESS_WITHDRAWAL_AND_COINBASE_PREFIX` | `Bytes1('0x02')` |
 
 ### Domain types
 

specs/phase0/deposit-contract.md

@@ -60,7 +60,7 @@ The amount of ETH (rounded down to the closest Gwei) sent to the deposit contrac
 
 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`.
+The withdrawal prefixes currently supported are `BLS_WITHDRAWAL_PREFIX`, `ETH1_ADDRESS_WITHDRAWAL_PREFIX`, and `ETH1_ADDRESS_WITHDRAWAL_AND_COINBASE_PREFIX`.
 Read more in the [validator guide](./validator.md#withdrawal-credentials).
 
 *Note*: The deposit contract does not validate the `withdrawal_credentials` field.

specs/phase0/validator.md

@@ -22,6 +22,7 @@ This is an accompanying document to [Ethereum 2.0 Phase 0 -- The Beacon Chain](.
     - [Withdrawal credentials](#withdrawal-credentials)
       - [`BLS_WITHDRAWAL_PREFIX`](#bls_withdrawal_prefix)
       - [`ETH1_ADDRESS_WITHDRAWAL_PREFIX`](#eth1_address_withdrawal_prefix)
+      - [`ETH1_ADDRESS_WITHDRAWAL_AND_COINBASE_PREFIX`](#eth1_address_withdrawal_and_coinbase_prefix)
   - [Submit deposit](#submit-deposit)
   - [Process deposit](#process-deposit)
   - [Validator index](#validator-index)
@@ -168,6 +169,26 @@ triggered by a user transaction that will set the gas price and gas limit as wel
 As long as the account or contract with address `eth1_withdrawal_address` can receive ETH transfers,
 the future withdrawal protocol is agnostic to all other implementation details.
 
+##### `ETH1_ADDRESS_WITHDRAWAL_AND_COINBASE_PREFIX`
+
+This is an extension of `ETH1_ADDRESS_WITHDRAWAL_PREFIX`.
+As with that prefix, this specifies a 20-byte Eth1 address `eth1_withdrawal_address`, which can be the address of either an externally owned account or of a contract.
+This address will be the recipient for all withdrawals.
+Additionally, blocks proposed by validators using this prefix **will be invalid** if the `coinbase` for those blocks is not equal to `eth1_withdrawal_address`.
+
+The `withdrawal_credentials` field must be such that:
+
+* `withdrawal_credentials[:1] == ETH1_ADDRESS_WITHDRAWAL_AND_COINBASE_PREFIX`
+* `withdrawal_credentials[1:12] == b'\x00' * 11`
+* `withdrawal_credentials[12:] == eth1_withdrawal_address`
+
+After the merge of the current Ethereum application layer (Eth1) into the Beacon Chain (Eth2),
+withdrawals to `eth1_withdrawal_address` will be normal ETH transfers (with no payload other than the validator's ETH)
+triggered by a user transaction that will set the gas price and gas limit as well pay fees.
+As long as the account or contract with address `eth1_withdrawal_address` can receive ETH transfers,
+the future withdrawal protocol is agnostic to all other implementation details.
+
+
 ### Submit deposit
 
 In Phase 0, all incoming validator deposits originate from the Ethereum 1.0 chain defined by `DEPOSIT_CHAIN_ID` and `DEPOSIT_NETWORK_ID`. Deposits are made to the [deposit contract](./deposit-contract.md) located at `DEPOSIT_CONTRACT_ADDRESS`.

tests/core/pyspec/eth2spec/test/phase0/block_processing/test_process_deposit.py

@@ -116,14 +116,36 @@ def test_new_deposit_eth1_withdrawal_credentials(spec, state):
     yield from run_deposit_processing(spec, state, deposit, validator_index)
 
 
+@with_all_phases
+@spec_state_test
+def test_new_deposit_eth1_withdrawal_and_coinbase_credentials(spec, state):
+    # fresh deposit = next validator index = validator appended to registry
+    validator_index = len(state.validators)
+    withdrawal_credentials = (
+        spec.ETH1_ADDRESS_WITHDRAWAL_AND_COINBASE_PREFIX
+        + b'\x00' * 11  # specified 0s
+        + b'\x59' * 20  # a 20-byte eth1 address
+    )
+    amount = spec.MAX_EFFECTIVE_BALANCE
+    deposit = prepare_state_and_deposit(
+        spec, state,
+        validator_index,
+        amount,
+        withdrawal_credentials=withdrawal_credentials,
+        signed=True,
+    )
+
+    yield from run_deposit_processing(spec, state, deposit, validator_index)
+
+
 @with_all_phases
 @spec_state_test
 def test_new_deposit_non_versioned_withdrawal_credentials(spec, state):
     # fresh deposit = next validator index = validator appended to registry
     validator_index = len(state.validators)
     withdrawal_credentials = (
         b'\xFF'  # Non specified withdrawal credentials version
-        + b'\x02' * 31  # Garabage bytes
+        + b'\x02' * 31  # Garbage bytes
     )
     amount = spec.MAX_EFFECTIVE_BALANCE
     deposit = prepare_state_and_deposit(