Increase the MAX_EFFECTIVE_BALANCE
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Original
Abstract
Increases the constant MAX_EFFECTIVE_BALANCE
, while keeping the minimum staking balance 32 ETH
. This permits large node operators to consolidate into fewer validators while also allowing solo-stakers to earn compounding rewards and stake in more flexible increments.
Motivation
As of October 3, 2023, there are currently over 830,000 validators participating in the consensus layer. The size of this set continues to grow due, in part, to the MAX_EFFECTIVE_BALANCE
, which limits the stake of a single validator to 32 ETH
. This leads to large amounts of "redundant validators", which are controlled by a single entity, possibly running on the same beacon node, but with distinct BLS signing keys. The limit on the MAX_EFFECTIVE_BALANCE
is technical debt from the original sharding design, in which subcommittees (not the attesting committee but the committee calculated in is_aggregator
) needed to be majority honest. As a result, keeping the weights of subcommittee members approximately equal reduced the risk of a single large validator containing too much influence. Under the current design, these subcommittees are only used for attestation aggregation, and thus only have a 1/N
honesty assumption.
With the security model of the protocol no longer dependent on a low value for MAX_EFFECTIVE_BALANCE
, we propose raising this value while keeping the minimum validator threshold of 32 ETH
. This increase aims to reduce the validator set size, thereby reducing the number of P2P messages over the network, the number of BLS signatures that need to be aggregated each epoch, and the BeaconState
memory footprint. This change adds value for both small and large validators. Large validators can consolidate to run fewer validators and thus fewer beacon nodes. Small validators now benefit from compounding rewards and the ability to stake in more flexible increments (e.g., the ability to stake 40 ETH
instead of needing to accumulate 64 ETH
to run two validators today).
Specification
Constants
Execution layer
Name | Value | Comment |
---|---|---|
CONSOLIDATION_REQUEST_TYPE | 0x02 | The EIP-7685 type prefix for consolidation request |
CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS | 0x01aBEa29659e5e97C95107F20bb753cD3e09bBBb | Where to call and store relevant details about consolidation request mechanism |
SYSTEM_ADDRESS | 0xfffffffffffffffffffffffffffffffffffffffe | Address used to invoke system operation on contract |
EXCESS_CONSOLIDATION_REQUESTS_STORAGE_SLOT | 0 | |
CONSOLIDATION_REQUEST_COUNT_STORAGE_SLOT | 1 | |
CONSOLIDATION_REQUEST_QUEUE_HEAD_STORAGE_SLOT | 2 | Pointer to the head of the consolidation request message queue |
CONSOLIDATION_REQUEST_QUEUE_TAIL_STORAGE_SLOT | 3 | Pointer to the tail of the consolidation request message queue |
CONSOLIDATION_REQUEST_QUEUE_STORAGE_OFFSET | 4 | The start memory slot of the in-state consolidation request message queue |
MAX_CONSOLIDATION_REQUESTS_PER_BLOCK | 1 | Maximum number of consolidation requests that can be dequeued into a block |
TARGET_CONSOLIDATION_REQUESTS_PER_BLOCK | 1 | |
MIN_CONSOLIDATION_REQUEST_FEE | 1 | |
CONSOLIDATION_REQUEST_FEE_UPDATE_FRACTION | 17 | |
EXCESS_INHIBITOR | 2**256-1 | Excess value used to compute the fee before the first system call |
FORK_TIMESTAMP | TBD | Mainnet |
Consensus layer
Name | Value |
---|---|
COMPOUNDING_WITHDRAWAL_PREFIX | Bytes1('0x02') |
MIN_ACTIVATION_BALANCE | Gwei(2**5 * 10**9) (32 ETH) |
MAX_EFFECTIVE_BALANCE | Gwei(2**11 * 10**9) (2048 ETH) |
Execution layer
Consolidation request
The new consolidation request is an EIP-7685 request with type 0x02
consisting of the following fields:
source_address
:Bytes20
source_pubkey
:Bytes48
target_pubkey
:Bytes48
The EIP-7685 encoding of a consolidation request is as follows. Note we simply return the encoded request value as returned by the contract.
request_type = CONSOLIDATION_REQUEST_TYPE request_data = dequeue_consolidation_requests()
Consolidation request contract
The contract has three different code paths, which can be summarized at a high level as follows:
- Add consolidation request - requires a
96
byte input, concatenated public keys of the source and the target validators. - Excess consolidation requests getter - if the input length is zero, return the current excess consolidation requests count.
- System process - if called by system address, pop off the consolidation requests for the current block from the queue.
Add Consolidation Request
If call data input to the contract is exactly 96
bytes, perform the following:
- Ensure enough ETH was sent to cover the current consolidation request fee (
check_fee()
) - Increase consolidation request count by
1
for the current block (increment_count()
) - Insert a consolidation request into the queue for the source address and pubkeys of the source and the target (
insert_withdrawal_request_into_queue()
)
Specifically, the functionality is defined in pseudocode as the function add_consolidation_request()
:
def add_consolidation_request(Bytes48: source_pubkey, Bytes48: target_pubkey): """ Add consolidation request adds new request to the consolidation request queue, so long as a sufficient fee is provided. """ # Verify sufficient fee was provided. fee = get_fee() require(msg.value >= fee, 'Insufficient value for fee') # Increment consolidation request count. count = sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_COUNT_STORAGE_SLOT) sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_COUNT_STORAGE_SLOT, count + 1) # Insert into queue. queue_tail_index = sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_QUEUE_TAIL_STORAGE_SLOT) queue_storage_slot = CONSOLIDATION_REQUEST_QUEUE_STORAGE_OFFSET + queue_tail_index * 4 sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot, msg.sender) sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot + 1, source_pubkey[0:32]) sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot + 2, source_pubkey[32:48] ++ target_pubkey[0:16]) sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot + 3, target_pubkey[16:48]) sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_QUEUE_TAIL_STORAGE_SLOT, queue_tail_index + 1)
Fee calculation
The following pseudocode can compute the cost of an individual consolidation request, given a certain number of excess consolidation requests.
def get_fee() -> int: excess = sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, EXCESS_CONSOLIDATION_REQUESTS_STORAGE_SLOT) require(excess != EXCESS_INHIBITOR, 'Inhibitor still active') return fake_exponential( MIN_CONSOLIDATION_REQUEST_FEE, excess, CONSOLIDATION_REQUEST_FEE_UPDATE_FRACTION ) def fake_exponential(factor: int, numerator: int, denominator: int) -> int: i = 1 output = 0 numerator_accum = factor * denominator while numerator_accum > 0: output += numerator_accum numerator_accum = (numerator_accum * numerator) // (denominator * i) i += 1 return output // denominator
Fee Getter
When the input to the contract is length zero, interpret this as a get request for the current fee, i.e. the contract returns the result of get_fee()
.
System Call
If the contract is called as SYSTEM_ADDRESS
with an empty input data, perform the following:
- The contract's queue is updated based on consolidation requests dequeued and the consolidation requests queue head/tail are reset if the queue has been cleared (
dequeue_consolidation_requests()
) - The contract's excess consolidation requests are updated based on usage in the current block (
update_excess_consolidation_requests()
) - The contract's consolidation requests count is reset to
0
(reset_consolidation_requests_count()
)
Specifically, the functionality is defined in pseudocode as the function process_consolidation_requests()
:
################### # Public function # ################### def process_consolidation_requests(): reqs = dequeue_consolidation_requests() update_excess_consolidation_requests() reset_consolidation_requests_count() return ssz.serialize(reqs) ########### # Helpers # ########### class ConsolidationRequest(object): source_address: Bytes20 source_pubkey: Bytes48 target_pubkey: Bytes48 def dequeue_consolidation_requests(): queue_head_index = sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_QUEUE_HEAD_STORAGE_SLOT) queue_tail_index = sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_QUEUE_TAIL_STORAGE_SLOT) num_in_queue = queue_tail_index - queue_head_index num_dequeued = min(num_in_queue, MAX_CONSOLIDATION_REQUESTS_PER_BLOCK) reqs = [] for i in range(num_dequeued): queue_storage_slot = CONSOLIDATION_REQUEST_QUEUE_STORAGE_OFFSET + (queue_head_index + i) * 4 source_address = address(sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot)[0:20]) source_pubkey = ( sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot + 1)[0:32] + sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot + 2)[0:16] ) target_pubkey = ( sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot + 2)[16:32] + sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, queue_storage_slot + 3)[0:32] ) req = ConsolidationRequest( source_address=Bytes20(source_address), source_pubkey=Bytes48(source_pubkey), target_pubkey=Bytes48(target_pubkey) ) reqs.append(req) new_queue_head_index = queue_head_index + num_dequeued if new_queue_head_index == queue_tail_index: # Queue is empty, reset queue pointers sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_QUEUE_HEAD_STORAGE_SLOT, 0) sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_QUEUE_TAIL_STORAGE_SLOT, 0) else: sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_QUEUE_HEAD_STORAGE_SLOT, new_queue_head_index) return reqs def update_excess_consolidation_requests(): previous_excess = sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, EXCESS_CONSOLIDATION_REQUESTS_STORAGE_SLOT) # Check if excess needs to be reset to 0 for first iteration after activation if previous_excess == EXCESS_INHIBITOR: previous_excess = 0 count = sload(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_COUNT_STORAGE_SLOT) new_excess = 0 if previous_excess + count > TARGET_CONSOLIDATION_REQUESTS_PER_BLOCK: new_excess = previous_excess + count - TARGET_CONSOLIDATION_REQUESTS_PER_BLOCK sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, EXCESS_CONSOLIDATION_REQUESTS_STORAGE_SLOT, new_excess) def reset_consolidation_requests_count(): sstore(CONSOLIDATION_REQUEST_PREDEPLOY_ADDRESS, CONSOLIDATION_REQUEST_COUNT_STORAGE_SLOT, 0)
Bytecode
caller push20 0xfffffffffffffffffffffffffffffffffffffffe eq push1 0xd3 jumpi push1 0x11 push0 sload dup1 push32 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff eq push2 0x019a jumpi push1 0x01 dup3 mul push1 0x01 swap1 push0 jumpdest push0 dup3 gt iszero push1 0x68 jumpi dup2 add swap1 dup4 mul dup5 dup4 mul swap1 div swap2 push1 0x01 add swap2 swap1 push1 0x4d jump jumpdest swap1 swap4 swap1 div swap3 pop pop pop calldatasize push1 0x60 eq push1 0x88 jumpi calldatasize push2 0x019a jumpi callvalue push2 0x019a jumpi push0 mstore push1 0x20 push0 return jumpdest callvalue lt push2 0x019a jumpi push1 0x01 sload push1 0x01 add push1 0x01 sstore push1 0x03 sload dup1 push1 0x04 mul push1 0x04 add caller dup2 sstore push1 0x01 add push0 calldataload dup2 sstore push1 0x01 add push1 0x20 calldataload dup2 sstore push1 0x01 add push1 0x40 calldataload swap1 sstore caller push1 0x60 shl push0 mstore push1 0x60 push0 push1 0x14 calldatacopy push1 0x74 push0 log0 push1 0x01 add push1 0x03 sstore stop jumpdest push1 0x03 sload push1 0x02 sload dup1 dup3 sub dup1 push1 0x01 gt push1 0xe7 jumpi pop push1 0x01 jumpdest push0 jumpdest dup2 dup2 eq push2 0x0129 jumpi dup3 dup2 add push1 0x04 mul push1 0x04 add dup2 push1 0x74 mul dup2 sload push1 0x60 shl dup2 mstore push1 0x14 add dup2 push1 0x01 add sload dup2 mstore push1 0x20 add dup2 push1 0x02 add sload dup2 mstore push1 0x20 add swap1 push1 0x03 add sload swap1 mstore push1 0x01 add push1 0xe9 jump jumpdest swap2 add dup1 swap3 eq push2 0x013b jumpi swap1 push1 0x02 sstore push2 0x0146 jump jumpdest swap1 pop push0 push1 0x02 sstore push0 push1 0x03 sstore jumpdest push0 sload dup1 push32 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff eq iszero push2 0x0173 jumpi pop push0 jumpdest push1 0x01 sload push1 0x01 dup3 dup3 add gt push2 0x0188 jumpi pop pop push0 push2 0x018e jump jumpdest add push1 0x01 swap1 sub jumpdest push0 sstore push0 push1 0x01 sstore push1 0x74 mul push0 return jumpdest push0 push0 revert
Deployment
The consolidation requests contract is deployed like any other smart contract. A special synthetic address is generated by working backwards from the desired deployment transaction:
{ "type": "0x0", "nonce": "0x0", "to": null, "gas": "0x3d090", "gasPrice": "0xe8d4a51000", "maxPriorityFeePerGas": null, "maxFeePerGas": null, "value": "0x0", "input": "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", "v": "0x1b", "r": "0x539", "s": "0x4b026bde3de3d21a", "hash": "0x5c86483822c8978690fd23fec89ba75e205c734020315827c50e2def49f924d4" }
Sender: 0xB64F31e716F43404Fc452Ad957e37B45B2A9AC86
Address: 0x0046BB33B9eA028AE30BAd20702e36Ea8099BBbb
Block processing
At the end of processing any execution block where block.timestamp >= FORK_TIMESTAMP
(i.e. after processing all transactions and after performing the block body requests validations) client software MUST take the following steps:
- Call the contract as
SYSTEM_ADDRESS
and empty input data to trigger the system subroutine execute. - Check that consolidation requests in the EIP-7685 requests list matches the list returned from
dequeue_consolidation_requests()
function of the smart contract respecting the order of the returned requests. If this condition does not hold, the block MUST be deemed invalid.
Consensus layer
The defining features of this EIP are:
- Increasing the
MAX_EFFECTIVE_BALANCE
, while creating aMIN_ACTIVATION_BALANCE
. The core feature of allowing variable size validators. - Allowing for multiple validator indices to be combined through the protocol. A mechanism by which large node operators can combine validators without cycling through the exit and activation queues.
- Adding execution layer partial withdrawals (part of EIP-7002). Allowing Execution Layer messages to trigger partial withdrawals in addition to full exits (e.g., a
100 ETH
validator can remove up to68 ETH
without exiting the validator). - Removing the initial slashing penalty (still in discussion). This reduces the risk of consolidation for large validators.
The Rationale section contains an explanation for each of these proposed core features. A sketch of the resulting changes to the consensus layer is included below.
- Add
COMPOUNDING_WITHDRAWAL_PREFIX
andMIN_ACTIVATION_BALANCE
constants, while updating the value ofMAX_EFFECTIVE_BALANCE
. - Create the
PendingDeposit
container, which is used to track incoming deposits in the weight-based rate limiting mechanism. - Update the
BeaconState
with fields needed for deposit and exit queue weight-based rate limiting. - Modify
is_eligible_for_activation_queue
to check againstMIN_ACTIVATION_BALANCE
rather thanMAX_EFFECTIVE_BALANCE
. - Modify
get_validator_churn_limit
to depend on the validator weight rather than the validator count. - Create a helper
compute_exit_epoch_and_update_churn
to calculate the exit epoch based on the current pending withdrawals. - Modify
initiate_validator_exit
to rate limit the exit queue by balance rather than the number of validators. - Modify
initialize_beacon_state_from_eth1
to useMIN_ACTIVATION_BALANCE
. - Modify
process_registry_updates
to activate all eligible validators. - Add a per-epoch helper,
process_pending_balance_deposits
, to consume some of the pending deposits. - Modify
get_validator_from_deposit
to initialize the effective balance to zero (it's updated by the pending deposit flow). - Modify
apply_deposit
to store incoming deposits instate.pending_balance_deposits
. - Modify
is_aggregator
to be weight-based. - Modify
compute_weak_subjectivity_period
to use the new churn limit function. - Add
has_compounding_withdrawal_credential
to check for the0x02
credential. - Modify
is_fully_withdrawable_validator
to check for compounding credentials. - Add
get_validator_excess_balance
to calculate the excess balance of validators. - Modify
is_partially_withdrawable_validator
to check for excess balance. - Modify
get_expected_withdrawals
to use excess balance.
Rationale
This EIP aims to reduce the total number of validators without changing anything about the economic security of the protocol. It provides a mechanism by which large node operators who control significant amounts of stake can consolidate into fewer validators. We analyze the reasoning behind each of the core features.
- Increasing the
MAX_EFFECTIVE_BALANCE
, while creating aMIN_ACTIVATION_BALANCE
.- While increasing the
MAX_EFFECTIVE_BALANCE
to allow larger-stake validators, it is important to keep the lower bound of32 ETH
(by introducing a new constant –MIN_ACTIVATION_BALANCE
) to encourage solo-staking.
- While increasing the
- Allowing for multiple validator indices to be combined through the protocol.
- For large staking pools that already control thousands of validators, exiting and re-entering would be extremely slow and costly. The adoption of the EIP will be much higher by allowing in-protocol consolidation.
- Adding execution layer partial withdrawals (part of EIP-7002).
- For validators that choose to raise their effective balance ceiling, allowing for custom partial withdrawals triggered from the execution layer increases the flexibility of the staking configurations. Validators can choose when and how much they withdraw but will have to pay gas for the EL transaction.
- Removing the initial slashing penalty (still in discussion).
- To encourage consolidation, we could modify the slashing penalties. The biggest hit comes from the initial penalty of
1/32
of the validator's effective balance. Since this scales linearly on the effective balance, the higher-stake validators directly incur higher risk. By changing the scaling properties, we could make consolidation more attractive.
- To encourage consolidation, we could modify the slashing penalties. The biggest hit comes from the initial penalty of
Backwards Compatibility
This EIP introduces backward incompatible changes to the block validation rule set on the consensus layer and must be accompanied by a hard fork. These changes do not break anything related to current user activity and experience.
Security Considerations
This change modifies committees and churn, but doesn't significantly impact the security properties.
Security of attestation committees
Given full consolidation as the worst case, the probability of an adversarial takeover of a committee remains low. Even in a high consolidation scenario, the required share of honest validators remains well below the 2/3 supermajority needed for finality.
Aggregator selection
In the original sharding roadmap, subcommittees were required to be secure with extremely high probability. Now with the sole responsibility of attestation aggregation, we only require each committee to have at least one honest aggregator. Currently, aggregators are selected through a VRF lottery, targeting several validator units that can be biased by non-consolidated attackers. This proposal changes the VRF lottery to consider weight, so the probability of having at least one honest aggregator is not worse.
Proposer selection probability
Proposer selection is already weighted by the ratio of their effective balance to MAX_EFFECTIVE_BALANCE
. Due to the lower probabilities, this change will slightly increase the time it takes to calculate the next proposer index.
Sync committee selection probability
Sync committee selection is also already weighted by effective balance, so this proposal does not require modifications to the sync protocol. Light clients can still check that a super-majority of participants have signed an update irrespective of their weights since we maintain a weight-based selection probability.
Churn invariants
This proposal maintains the activation and exit churn invariants limiting active weight instead of validator count. Balance top-ups are now handled explicitly, being subject to the same activation queue as full deposits.
Fee Overpayment
Calls to the system contract require a fee payment defined by the current contract state. Overpaid fees are not returned to the caller. It is not generally possible to compute the exact required fee amount ahead of time. When adding a consolidation request from a contract, the contract can perform a read operation to check for the current fee and then pay exactly the required amount. Here is an example in Solidity:
function addConsolidation(bytes memory srcPubkey, bytes memory targetPubkey) private {
assert(srcPubkey.length == 48);
assert(targetPubkey.length == 48);
// Read current fee from the contract.
(bool readOK, bytes memory feeData) = ConsolidationsContract.staticcall('');
if (!readOK) {
revert('reading fee failed');
}
uint256 fee = uint256(bytes32(feeData));
// Add the request.
bytes memory callData = bytes.concat(srcPubkey, targetPubkey);
(bool writeOK,) = ConsolidationsContract.call{value: fee}(callData);
if (!writeOK) {
revert('adding request failed');
}
}
Note: the system contract uses the EVM CALLER
operation (Solidity: msg.sender
) to get the address used in the consolidation request, i.e. the address that calls the system contract must match the 0x01 withdrawal credential recorded in the beacon state.
Using an EOA to request consolidations will always result in overpayment of fees. There is no way for an EOA to use a wrapper contract to request a consolidation. And even if a way existed, the gas cost of returning the overage would likely be higher than the overage itself. If requesting consolidations from an EOA to the system contract is desired, we recommend that users perform transaction simulations to estimate a reasonable fee amount to send.
Copyright
Copyright and related rights waived via CC0.
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