[WIP]Feat/zcash

[soralit]

Keystone Zcash UR Registries

This protocol is based on the Uniform Resources. It describes the data schemas (UR Registries) used in Zcash integrations.

Introduction

Keystone's QR workflow involves two main steps: linking the wallet and signing data, broken down into three sub-steps:

1. Wallet Linking: Keystone generates a QR code with public key info for the Watch-Only wallet to scan and import.
2. Transaction Creation: The Watch-Only wallet creates a transaction and generates a QR code for Keystone to scan, parse, and display.
3. Signing Authorization: Keystone signs the transaction, displays the result as a QR code for the Watch-Only wallet to scan and broadcast.

Two UR Registries are needed for these steps, utilizing the Partially Created Zcash Transaction structure.

Zcash Accounts

Unified Full Viewing Key (UFVK)

UFVK is a standard account expression format in Zcash as per ZIP-316. It consists of:

1. Transparent
2. Sprout
3. Sapling
4. Orchard

This protocol focuses on the Transparent and Orchard components.

CDDL for Zcash Accounts

The specification uses CDDL and includes crypto-hdkey and crypto-key-path specs defined in https://github.com/BlockchainCommons/Research/blob/master/papers/bcr-2020-007-hdkey.md.

zcash-accounts = {
    master-fingerprint: uint32, ; the master fingerprint to identify the wallet
    accounts: [+ zcash-ufvk],
    ? origin: text, ; source of data, e.g., Keystone
}

zcash-ufvk = {
    ? transparent: crypto-hdkey,
    orchard: zcash-fvk,
    ? name: text,
}

zcash-fvk = {
    key-path: crypto-key-path,
    key-data: bytes,
}

zcash-ufvk describes the UFVK of a Zcash account. Each seed has multiple accounts with different indexes. For index 0, zcash-ufvk should contain a BIP32 extended public key with path M/44'/133'/0' (transparent) and an Orchard FVK with path M_orchard/32'/133'/0' (Orchard).

CDDL for Zcash PCZT

zcash-pczt {
    data: bytes, ; Zcash PCZT, signatures inserted after signing.
}

[daira]

ZIP 32 specifies a 16-byte seed fingerprint: https://zips.z.cash/zip-0032#seed-fingerprints
It's a byte array so endian-independent.

[soralit]

It's good to use this seed fingerprint instead.

[daira]

Specify that:

• M is defined as in https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#master-key-generation
• M_orchard (we use $m_{\mathsf{Orchard}}$) is defined as in https://zips.z.cash/zip-0032#orchard-master-key-generation .

133' is for mainnet. Like other coins, we use 1' for testnet as specified in SLIP 44.