Notaries

The notary is Corda’s uniqueness consensus service. The notary’s primary role is to prevent double-spends by ensuring each transaction contains only unique unconsumed input states An immutable object representing a fact known by one or more participants at a specific point in time. You can use states to represent any type of data, and any kind of fact. . It also acts as the time-stamping authority. Every transaction includes a time window and it can only be notarized during that window. A notary service is formed by one or more notary workers that together form a notary cluster. The cluster’s signature is obtained once it verifies that a proposed transaction’s input states have not already been consumed by a prior transaction. Upon determining this, the notary cluster will either:

• Sign the transaction in cases where all input states are found to be unique.
• Reject the transaction and flag that a double-spend attempt has occurred in cases where any of the input states are identical to those already encountered in a previous transaction.

Every state has an appointed notary cluster, so the cluster only notarizes a transaction if it is the appointed notary cluster of all of the transaction’s input states. A network can have several notary clusters, all running different consensus algorithms.

Multiple Notaries

Each Corda network can have multiple notary clusters. This has several benefits:

• Choice of protocol: Nodes can choose the preferred notary cluster on a per-transaction basis.
• Load balancing: Spreading the transaction load over multiple notary clusters allows higher transaction throughput for the platform overall.
• Low latency: Latency can be minimized by choosing a notary cluster physically closer to the transacting parties.