Synchronizer¶

A Synchronizer is a foundational part of the Canton architecture that provides two main functionalities:

Sequencing: Ordered and confidential communication between independent participant nodes (validators).
Mediating: Transaction coordination as part of the two-phase commit protocol to provide atomicity and privacy.

Canton is designed as a network of networks where participant nodes may be connected to multiple Synchronizers at the same time.

Role in the Canton architecture¶

Message Queue and Ordering: The Synchronizer serves as a secure message queue, receiving encrypted transaction requests from participant nodes and ensuring they are ordered consistently. This ordering is critical for resolving potential conflicts and achieving consistent outcomes.
Privacy by Design: Unlike traditional public blockchains where transaction data is public, Canton’s Synchronizer can not decrypt the transaction payloads. Messages are always encrypted end-to-end between the relevant participants (validators). The Synchronizer only sees encrypted envelopes and their metadata for routing and ordering, maintaining privacy for sensitive transaction information.
Not a Validator: It’s important to note that the Synchronizer is not responsible for validating the transaction contents. That responsibility lies with the stakeholder participant nodes (validators) involved in a given transaction, using Canton’s two-phase commit protocol. The Synchronizer merely ensures the consistent sequencing and delivery of these transaction requests and coordinates the outcomes of the transactions.

Sequencer: The Sequencer is responsible for delivering the messages to the designated recipients adhering to the atomic multicast properties with privacy.
Mediator: The Mediator works in conjunction with the Sequencer. It aggregates transaction confirmations from the involved stakeholder participant nodes (validators) and either approves or rejects a transaction based on the confirmations. It plays a key role in the two-phase commit protocol and provides privacy between the different participants involved in a transaction.
Ordering Layer: The ordering layer establishes a consistent ordering of messages going through the Sequencer and assigns timestamps to the ordered messages, which is fundamental for conflict detection of transactions.

Centralized Synchronizers: While Canton is designed for decentralization, a private Canton deployment can use a centralized Synchronizer operated by a single entity. This is suitable for closed consortia or internal enterprise use cases.
Decentralized Synchronizers: This is the more public and robust form. The Global Synchronizer is operated by a network of independent “Super Validators” who jointly run the Sequencers using Byzantine fault-tolerant (BFT) consensus and Mediators with BFT state machine replication. This offers high resiliency and security in the sense of not relying on a single trusted third party.