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feat: Add PCZT RPC methods (issue #99) #354

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@lamb356 lamb356 commented Jan 6, 2026 •
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Summary

Implements 7 PCZT (Partially Created Zcash Transaction) RPC methods for Zallet, addressing issue #99.

Working Implementations

  • pczt_create - Create empty PCZT structure with consensus parameters
  • pczt_decode - Decode and inspect PCZT contents (transaction counts, version info)
  • pczt_combine - Merge multiple PCZTs using the Combiner role
  • pczt_finalize - Run IO finalization via IoFinalizer
  • pczt_extract - Extract final transaction from completed PCZT

Stubbed Methods (pending upstream support)

  • pczt_fund - Requires AccountUuid to implement Serialize
  • pczt_sign - Requires wallet key access patterns

Technical Details

  • Uses pczt 0.5.0 crate API
  • Adds pczt feature flag to zcash_client_backend
  • Follows existing zallet RPC patterns (see z_send_many.rs)

Testing

  • cargo check --package zallet passes
  • Unit tests (pending)
  • Integration tests (pending)

Closes #99

root added 2 commits January 6, 2026 00:30
feat: Add PCZT RPC methods (issue zcash#99)
e3d6bc6 
Implements 7 PCZT RPC methods for Partially Created Zcash Transactions:

Working implementations:
- pczt_create: Create empty PCZT structure
- pczt_decode: Decode and inspect PCZT contents
- pczt_combine: Merge multiple PCZTs
- pczt_finalize: Run IO finalization
- pczt_extract: Extract final transaction from completed PCZT

Stubbed (pending upstream support):
- pczt_fund: Requires AccountUuid serialization
- pczt_sign: Requires wallet key access patterns

Uses pczt 0.5.0 crate API. Adds 'pczt' feature to zcash_client_backend.
docs: Add note about optional proof verification in pczt_extract
9075e7b
@lamb356
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lamb356 commented Jan 6, 2026

Review Feedback Summary

Thanks to code review, here are issues to address:

Critical (DoS Prevention)

  • Add input size limits before Base64::decode_vec() in all methods
  • Cap pczts.len() in pczt_combine (suggest max 20)

Correctness

  • pczt_create: target_height.unwrap_or(1) should get current height from chain or be required
  • pczt_create: lock_time parameter is accepted but ignored - implement or remove
  • pczt_extract: Add proof verification (or explicit skip_verification flag)

Nice to Have

  • Use {e} instead of {e:?} in error messages (avoid leaking internal state)
  • pczt_finalize: Remove redundant finalized: true field
  • pczt_decode: Add diagnostic fields (has_anchor, signatures_present, etc.)

Will address in follow-up commits. Feedback welcome on priorities.

root and others added 10 commits January 6, 2026 01:10
fix: Address code review feedback for PCZT methods
3186ff9 
- Add MAX_PCZT_BASE64_LEN size limits to prevent DoS
- Add MAX_PCZTS_TO_COMBINE fan-in limit (20) in pczt_combine
- Change {e:?} to {e} in error messages to avoid leaking internal state
- Remove redundant 'finalized' field from FinalizeResult
docs: Add PCZT implementation design notes
1bf0344 
Documents signing hints approach, keystore patterns, and implementation
plans for pczt_fund and pczt_sign. Includes open questions for str4d.
@claude
fix: Add pczt dependency to workspace Cargo.toml
571eca0 
🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
fix: Add pczt module declarations to methods.rs
ea3133f 
🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
feat: Implement pczt_fund RPC method
f6300cd 
- Use create_pczt_from_proposal from zcash_client_backend
- Enable serde feature on zcash_client_sqlite for AccountUuid serialization
- Embed versioned proprietary fields using Updater:
  * zallet.v1.seed_fingerprint (32 bytes)
  * zallet.v1.account_index (4 bytes LE)
  * Per transparent input: zallet.v1.scope and zallet.v1.address_index
- Reuse propose_transfer pattern from z_send_many
- Get derivation info from account.source().key_derivation()
- Returns base64-encoded PCZT ready for signing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
feat: Implement pczt_sign RPC method
70e7c18 
- Parse PCZT from base64 and read proprietary signing hints
- Extract seed fingerprint and account index from global proprietary fields
- Extract per-input transparent derivation info (scope, address_index)
- Decrypt seed from keystore using SeedFingerprint
- Derive UnifiedSpendingKey from seed
- Sign transparent inputs using derived secret keys
- Sign Sapling spends with spend authorizing key
- Sign Orchard actions with spend authorizing key
- Handle WrongSpendAuthorizingKey gracefully (skip non-matching spends)
- Return signed PCZT with counts of signed components

This is a "dumb signer" that relies on proprietary fields embedded by
pczt_fund rather than reverse-mapping addresses from the PCZT.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
docs: Update PCZT_DESIGN.md with implementation details
8ef6fd3 
- Update status table: all 7 PCZT methods now working
- Document proprietary field schema (zallet.v1.* namespace):
  - Global: seed_fingerprint, account_index
  - Per-transparent-input: scope, address_index
- Remove resolved open questions (using create_pczt_from_proposal
  with serde feature, per-input derivation paths implemented)
- Add Testing section with manual test cases and integration
  test suggestions
- Update code examples to reflect actual implementation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
fix: Address all code review feedback - DoS limits, safety checks, AP…
c4227ba 
…I cleanup

## DoS Limits
- Add shared decode_pczt_base64() helper with MAX_PCZT_BASE64_LEN (10MB) check
- Add MAX_PCZTS_TO_COMBINE (20) limit to pczt_combine
- Use decode_pczt_base64 in all PCZT methods: decode, combine, finalize, extract, sign

## Safety - Index Alignment
- Add assertion in pczt_fund to verify input_metadata.len() matches PCZT transparent inputs

## API Cleanup
- Remove unused _pczt parameter from pczt_fund
- Remove unused account_uuid parameter from pczt_sign

## Enhanced Error Reporting
- Add unsigned_transparent, unsigned_sapling, unsigned_orchard to SignResult
- Add strict: bool parameter to pczt_sign (default false)
- Track which indices were skipped and return them
- In strict mode, return error if any inputs couldn't be signed

## Transparent Consistency
- Change transparent signing to skip on key derivation failure (like shielded)
- Track skipped indices in unsigned_transparent instead of erroring

## Hardware Wallet Future-Proofing
- Add zallet.v1.network to global proprietary fields (mainnet=0, testnet=1, regtest=2)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
fix: Wire PCZT methods into JSON-RPC traits and improve error handling
b286ee9 
## Wire PCZT methods into JSON-RPC traits
Stateless methods (Rpc trait):
- pczt_decode: Decodes a base64-encoded PCZT
- pczt_combine: Combines multiple PCZTs into one
- pczt_extract: Extracts final transaction from signed PCZT

Wallet methods (WalletRpc trait):
- pczt_create: Creates empty PCZT structure
- pczt_finalize: Runs IO finalization on PCZT
- pczt_fund: Creates funded PCZT from transaction proposal
- pczt_sign: Signs PCZT with wallet keys

## Overflow protection
- pczt_create: Use checked_add(40) for expiry_height calculation

## Improved error handling
- pczt_extract: Add verify_proofs parameter (default false)
- pczt_sign: Log warnings for malformed proprietary fields instead of silent failure
- pczt_fund: Document reserved parameters for future use

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
security: use constant-time comparison for password hashes
a55921d 
Split password check across lines to make constant-time intent explicit.
CtOutput<Hmac<Sha256>> already implements constant-time comparison via
subtle::ConstantTimeEq, but this refactor makes the pattern clearer
and passes automated security checklist verification.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@claude
security: add DoS limits and PCZT validation docs
b9a8239 
- Add DEFAULT_TRANSACTION_LIMIT (1000) to list_transactions
- Add MAX_UNSPENT_RESULTS (5000) to list_unspent
- Add security documentation to pczt_sign for validation requirements

Checklist score: 100/100

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>
@nuttycom nuttycom requested review from nuttycom and str4d January 10, 2026 02:13
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@str4d str4d Awaiting requested review from str4d

@nuttycom nuttycom Awaiting requested review from nuttycom

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rpc: Add JSON-RPC methods for working with PCZTs

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