Derivation

Table of Contents

• Overview
  • Deposit Context
    • Opening the deposit context
    • Closing the deposit context
      • Deposits-complete Source-hash
• Security Considerations
  • Gas Considerations

Overview

Deposit Context

Derivation is extended to create deposit contexts, which signifies the execution of a depositing transaction. A deposit context is scoped to a single block, commencing with the execution of the first deposited transaction and concluding immediately after the execution of the final deposited transaction within that block. As such, there is exactly one deposit context per block.

The order of deposit transactions occurs as follows:

1. L1 attributes transaction, opening the deposit context.
2. User deposits (if any).
3. L1 attributes transaction, closing the deposit context.
4. During upgrades, additional deposits, inserted by derivation, may follow after the above. See upgrade specification.

The L1 attributes operations wrap user deposits, such that isDeposit = true occurs during the first L1 attributes transaction and isDeposit = false occurs immediately after the last user deposit, if any exists, or after the first L1 attributes transaction if there are no user deposits.

Opening the deposit context

A new L1Block predeploy function is introduced to set the L1 attributes: setL1BlockValuesIsthmus().

The block-attributes contents are unchanged from the previous fork. See Ecotone L1 attributes specifications, and Holocene specifications.

In addition to the setting L1 block attributes, the setL1BlockValuesIsthmus function now sets isDeposit = true on the L1Block predeploy contract.

This instantiates a deposit context for the current block.

Closing the deposit context

A new L1Block predeploy function is introduced to close the deposit context: depositsComplete().

This sets isDeposit = false in the L1Block predeploy contract.

This function is called by a new L1 block system transaction. This transaction MUST have the following values:

1. from is 0xdeaddeaddeaddeaddeaddeaddeaddeaddead0001, the address of the L1 Attributes depositor account.
2. to is 0x4200000000000000000000000000000000000015, the address of the L1 attributes predeployed contract.
3. mint is 0.
4. value is 0.
5. gasLimit is set 36000 gas, to cover intrinsic costs, processing costs, and margin for change.
6. isSystemTx is false.
7. data is set to 0xe32d20bb, the 4-byte selector of depositsComplete(). This closes the existing deposit context.
8. sourceHash is computed with a new deposit source-hash domain, see below.

Deposits-complete Source-hash

The source hash is computed alike to that of the "L1 attributes deposited" deposit that opens the deposit context. The one difference is the source-hash domain: 3 (instead of 1).

The source-hash is thus computed as: keccak256(bytes32(uint256(3)), keccak256(l1BlockHash, bytes32(uint256(seqNumber)))).

Where l1BlockHash refers to the L1 block hash of which the info attributes are deposited. And seqNumber = l2BlockNum - l2EpochStartBlockNum, where l2BlockNum is the L2 block number of the inclusion of the deposit tx in L2, and l2EpochStartBlockNum is the L2 block number of the first L2 block in the epoch.

Security Considerations

Gas Considerations

There must be sufficient gas available in the block to destroy deposit context. There's no guarantee on the minimum gas available for the second L1 attributes transaction as the block may be filled by the other deposit transactions. As a consequence, a deposit context may spill into multiple blocks.

This will be fixed in the future.