Usability

The usability model for Zcash MSPA is as follows:

• Users may install and utilize a variety of wallets. More options are generally better.
• A user can freely create as many addresses as they need or desire at no cost.
• Each address controls a distinct set of ZEC funds.
• Each address is controlled entirely by a spend authority: anyone with knowledge of this spend authority can observe an address's entire history and spend any funds.
• Each address has an associated viewing key which allows anyone with knowledge thereof to view the entire history and future interactions of the address. However, a viewing key cannot spend any funds held by an address or effect any other changes. Anyone with knowledge of a spend authority can derive the associated viewing key. It is not possible to determine the spend authority given a viewing key.
• Given a destination address, a wallet holding a spend authority can initiate a transfer of funds controlled by that spend authority to be received by the destination address. When a sending wallet initiates a transfer, it generates all necessary information locally non-interactively¹, then it interacts with the Zcash MSPA to effect the transfer.
• When such a transfer is initiated, it will either become finalized by the protocol, or it will fail to finalize in a known limited amount of time.
• The protocol futher requires various fees to enable reliability and resilience which are requirements of safety. [TODO: Flesh out how fees relate to MSPA better.]

Wallet Data Availability: In a crucial departure from modern Zcash and many cryptocurrencies, the Zcash MSPA does not directly support data availability for wallets!

This means that wallets bear the sole responsibility for ensuring:

• received funds are available to be spent
• history is preserved
• restoring from a backup is successful

Wallets may rely on one or more wallet data availability providers to achieve this goal, as described in the Wallet Data Availability section.