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. Backchain resolution verifies that all transactions through the backchain have been notarized by a notary allowed on the network at the time of that transaction’s notarization. This verification is based on the network group parameters, which Corda also distributes with the backchain.

A notary service runs a notary protocol, which dictates the consensus algorithm and additional validation performed. In Corda 5.1, only the non-validating notary protocol is supported, which performs minimal additional checks beyond double-spend and time-window validation.

Data Visibility

The non-validating notary protocol maintains a degree of privacy by only revealing the information about a transaction that is strictly necessary to perform validation. Below is a summary of which specific transaction components are revealed:

The protocol also records the calling party’s identity in the form of its X.500 A series of international standards defining a global directory service protocol for computer networks. It provides a structured framework for storing, accessing, and managing information about network resources and users in a hierarchical and distributed manner. Distinguished Name.

[1] A state reference is composed of the issuing transaction’s ID and the state’s position in the outputs. It does not reveal what kind of state it is or its contents. [2] Output states are not revealed, but the total number of output states are communicated to allow the protocol to track unspent states.

Pluggable Notaries

The notary is implemented as a special app on the application network, consisting of a client plug-in included with an application workflow app, and a server component that needs to be installed as a notary member with its own virtual node.

The client plug-in and the server component define the protocol used by this notary.

Multiple Notaries

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

• Choice of protocol: Once multiple notary protocols are implemented, 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.

Changing Notaries

A notary cluster will only sign a transaction if it is the appointed notary cluster of all the transaction’s input states. However, there are cases in which it may be necessary to change a state’s appointed notary cluster. These include:

• When a single transaction needs to consume several states that have different appointed notary clusters.
• When a node would prefer to use a different notary cluster for a given transaction due to privacy or efficiency concerns.

Before these transactions can be created, the states must first all be re-pointed to the same notary cluster. This is achieved using a special notary-change transaction. This has not been implemented for this version of Corda.