Casper Hybrid PRD

### Purpose
Background

- Enterprise blockchain implementations are typically private networks of a small number of nodes that are managed either in a cloud provider or bare metal, depending on the organization’s internal IT compliance requirements.

- Enterprises are choosing private networks for the same reasons they started with private cloud - privacy, comfort and control. For the foreseeable future, they will use private instances for their purpose.

- A private blockchain fully under the control of its' owner doesn’t provide the security guarantees that come with the public network. Casper also supports the social consensus feature that does enable global state modification in the event of an emergency.

### Business Goals:

**Provide a mechanism that draws security from the public protocol into private blockchains.**
**Drive utilization of the public chain in private blockchain deployments.**

### Features, Functionality & Behavior

- Block hashes of the private chain are sent to the public blockchain in a transaction.
- Frequency of block hashes can be configured - ex: register every 10th block
- A configuration file for the product specifies the frequency of block registrations.
- Configuration file also contains a set of node endpoints to send transactions
- Wallet address and pem file for key to sign transactions
- Block hashes that have been registered to the public Casper network are matched up with the transaction data from the public protocol - so proofs can be provided that the blocks have not been modified.
- Application runs on a node and sends the block hashes as new blocks are finalized by the network.