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Mantle is a Bedrock component that serves as the operating system of Logos. It provides essential functionality that allows nodes to participate in Bedrock Services, as well as providing minimal operations to enable Native Zones and Sovereign Zones to interact with Bedrock. It is also responsible for handling Logos notes, which are Bedrock-native fungible tokens.
Mantle maintains a restricted ledger that provides a very limited execution environment and operations to support Bedrock Services, and is primarily concerned with fee payment for Mantle operations. This ledger keeps track of fungible assets known as notes, which are bound to their owners. Mantle notes are stored by Logos nodes in a dictionary mapping notes to their unique note identifiers.
Note transfers are effected by using Ledger transactions, which are based on the UTXO model. To transfer value, a sender spends their note and creates an equivalent new note belonging to the recipient. A spent note can never be spent again. All Logos nodes execute Ledger transactions independently to ensure that the ledger state is updated correctly.
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Native Zones remain a work in progress at this time.
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Mantle operations are the way Logos nodes interact with Bedrock Services, and allow Zones to interact with Bedrock. Operations are submitted to Mantle via Ledger transactions, with each transaction potentially including several operations. The cost of executing operations is paid for by gas fees, denoted in notes.
Logos nodes use Mantle operations to indicate their participation in Bedrock Services, with Mantle providing a locking mechanism used to incentivise correct behaviour by Service participants. The operations supported by Mantle include staking notes for participation in Bedrock Services, paying rewards to compensate participants, and unstaking notes.
Mantle operations allow for Native Zones to be created and updated. An update to the Native Zone state must be accompanied by a proof that the Native Zone ledger was updated according to the Common Ledger rules, and another proof that the Zone data was updated in accordance with that Zone’s state transition function. The availability of the Native Zone’s data is also verified so it can be recovered in case an executor attempts to withhold it.
Mantle can also serve as a censorship resistant message delivery mechanism for Zones, allowing Zone executors and sequencers to send information to each other and engage in coordinated action. These messages can be recorded on the blockchain permanently, or only for temporary storage in the form of a blob, which are discussed in more detail in the LogosDA section. This form of message passing facilitates cross-Zone interaction including arranging atomic transactions and state updates.
Mantle channels are lightweight virtual chains overlaid on top of the Logos Blockchain. The purpose of Mantle channels is to immediately enforce the correct ordering of transactions from Zones. These channels are implemented as permissioned, ordered logs of messages signed by a sequencer. These messages usually take the form of state updates from a particular Zone. Channels also provide several key features to Sovereign Zones, which are described below.
Mantle channels ensure that their transactions will eventually be included on-chain in the correct order, regardless of how the Logos Blockchain may fork or reorganise. This allows new transactions that depend on earlier ones to be submitted immediately, without waiting for finality. An example with two channels is shown below:
A diagram illustrating how two Mantle Channels are included in the Logos Blockchain.
It is important to note that Mantle channels can only be relied on if the sequencer is trusted to act honestly. In the absence of this assumption, users must wait for the true blockchain finality.
A channel may have one or several sequencers; in the latter case, the sequencers take turns publishing messages according to a round-robin schedule. Unresponsive sequencers lose their turn via an automated timeout. A given threshold of sequencers may also modify the sequencer list or change other channel properties by signing a message together, allowing an honest majority to remove a malicious sequencer. This form of decentralised Sovereign Zone sequencing distributes the potential for MEV extraction across a set of parties rather than concentrating it as in the single-sequencer rollup design.