ZIP-244: Implement transaction authorization hashes

[teor2345]

Implement (but not validate) ZIP-244 transaction authorization hashes.

Blockers

Specifications

• clarify the auth data hash tree construction: ZIP 244: Clarify contruction of hashAuthDataRoot zcash/zips#520

Motivation

ZIP-244 creates non-malleable transaction identifiers that commit to all transaction data except for attestations to transaction validity. (That is, signatures and proofs.)

ZIP-244 also adds a transaction authorization hash, which is hash-chained to the block commitment (#1567) and placed in the block commitment fields.

Describe the solution you'd like

We should implement or integrate this new transaction digest algorithm in Zebra as per:

• https://zips.z.cash/zip-0244
• https://zips.z.cash/zip-0225#modifications-to-zip-244

This will include:

Update the block::Commitment for NU5:

• Add the transaction authorization hash to the block header commitment field (Zebra-specific)
  • depends on ZIP-221: Block Header Chain History Commitment #1567

Transaction authorization hashes

• implement transaction authorization hashes using librustzcash

Alternative Implementations

The ECC have implemented a version of this in Rust in the librustzcash library, we should be able to either port some of that code or learn from that code to implement the Zebra version.

Follow up

Validation is done in #2562

[mpguerra]

Moved to Sprint 13

[conradoplg]

I've updated the description:

• Adding the hash to the block was moved to Add hashAuthDataRoot to Block network messages, and semantically verify it #2336
• I changed the text to require only the hash computation and not validation

With this I think we can remove this blocking on #2562 and close this (implemented in #2547). @mpguerra I'll leave this for you to confirm