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Mithril aggregator node

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A Mithril aggregator is a trustless node responsible for coordinating the activities of Mithril signer nodes. It gathers the individual signatures from the signer nodes to generate Mithril multi-signatures along with their corresponding certificates. Additionally, the aggregator is in charge of creating and maintaining the archive for the ledger state snapshot.

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Trustless orchestration​

The primary objective of the Mithril aggregator is to coordinate and synchronize the production of Mithril multi-signatures:

  • When a new snapshot is ready to be produced (and certified), the Mithril aggregator generates and broadcasts a fresh beacon to inform Mithril signers of the specific time reference to employ in computing the message (or digest) for signing

  • It is also responsible for advertising the verification keys (Mithril public keys) of all the registered Mithril signers

  • The beacon, the current protocol parameters, and the available verification keys are compiled and shared in a pending certificate

  • Mithril signers can register with it to participate in the signature process later on.

An important point to note is that the Mithril aggregator operates in a trustless manner:

  • Anyone on the network can run an aggregator

  • The aggregator doesn't broadcast any sensitive information, such as the message requiring signing. The signer nodes handle the direct computation of this information from a Cardano node on which they operate.

Additionally, when it comes to aggregating individual signatures into Mithril multi-signatures, the aggregator doesn't need to represent a portion of the total stake within the Cardano network.

Multi-signature and certificate production​

The Mithril aggregator oversees the creation of Mithril multi-signatures along with their associated certificates for a part and/or the entirety of the ledger state (snapshots):

  • Previously registered Mithril signers generate individual signatures. These signatures are then sent to the Mithril aggregator for validation and storage.

  • Once the quorum of individual signatures has been reached, the Mithril aggregator can generate a multi-signature.

  • Subsequently, the Mithril aggregator combines the multi-signature with relevant metadata to create a Mithril certificate. This certificate will later be utilized by the Mithril client to authenticate a snapshot's legitimacy.

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For more information about the Mithril certificate chain, see the certificate chain overview.

Snapshot artifacts production​

In its initial version, the Mithril aggregator also handles the production of artifacts associated with the snapshot (such as the snapshot archive, which will be used later by a Mithril client).

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It's important to note that this role is presently undertaken for the sake of convenience. However, it's planned that in the long run, the production of artifacts will be assigned to a distinct Mithril snapshotter node.

Once the snapshot artifact is created, it can be synchronized on various locations:

  • On the Mithril aggregator itself
  • On any cloud platform that offers a CDN
  • On a distinct peer-to-peer network, such as IPFS or BitTorrent.

The Mithril certificate is part of a chain of certificates that are essential for snapshot authenticity verification and is stored in either of the following ways:

  • On the Mithril aggregator itself
  • On any accessible storage, such as cloud storage, for instance.

Distribution of snapshot artifacts and certificates​

If the Mithril aggregator stores the snapshot artifacts and/or the certificates, it can function as a distribution point for this data to remote clients. The clients can then use the artifacts as needed and verify their authenticity.

Under the hood​

In its initial version, the Mithril aggregator comprises two main components:

  • A REST API that allows Mithril signers to:
    • Retrieve verification keys of other registered signers
    • Register their own verification keys
    • Register their individual signatures.
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The Mithril aggregator's REST API documentation can be found here.

  • A runtime powered by a state machine:
    • The runtime operates synchronously and is scheduled to execute at regular intervals
    • It encompasses three potential states: IDLE, READY, and SIGNING
    • The runtime effectively manages state transitions
    • The runtime structure is illustrated in the diagram below:

Aggregator Runtime