SeedPass/reports/protocol/protocol-report-2026-02-26.md

Protocol Compliance Report - 2026-02-26

Agent: protocol-research-agent Focus: Protocol Inventory & Compliance Assessment

Executive Summary

The codebase relies heavily on standard libraries (cryptography, bip-utils, nostr-sdk, pyotp) for cryptographic and protocol implementations, ensuring a high baseline of compliance. Most protocol implementations delegate to these libraries directly.

One potential deviation from standard specifications was identified in the local BIP85 implementation regarding the application number used for symmetric key derivation.

Findings

1. Strong Library Usage

• BIP39/32: bip-utils is used consistently.
• Crypto: cryptography (hazmat) is used for AES-GCM, HKDF, and Ed25519.
• Nostr: nostr-sdk (Rust bindings) handles protocol complexity.

2. BIP85 Custom Derivation Path

The implementation in src/local_bip85/bip85.py uses app_no=2 for symmetric key derivation:

def derive_symmetric_key(self, index: int = 0, app_no: int = 2) -> bytes:

According to BIP-85, app_no mappings are:

• 0: BIP32
• 2: WIF (Wallet Import Format) - Wait, spec usually assigns 2 to WIF.
• 128: Hex

However, the implementation derives raw entropy bytes for a symmetric key using app_no=2. If this is intended to match WIF generation logic, it might be acceptable, but typically symmetric keys (Hex) use app_no=128. Risk: Low (internal consistency is maintained), but interoperability with other BIP85 wallets for this specific derivation might be limited.

3. BIP39 Word Count Default

The derive_entropy method defaults word_count to entropy_bytes if word_count is None for app_no=39.

if app_no == 39:
    if word_count is None:
        word_count = entropy_bytes

This is safe as long as derive_mnemonic (the primary caller) passes explicit words_num. Direct calls to derive_entropy with app_no=39 and word_count=None could result in non-standard derivation paths (e.g., .../16'/... for 16 bytes entropy).

Recommendations

1. Document app_no=2 usage: Clarify in comments why 2 is used for symmetric keys (legacy or specific compatibility).
2. Add Compliance Tests: Verify derive_entropy produces expected output vectors (if available) or at least remains stable.
3. Monitor nostr-sdk updates: Ensure the Rust bindings stay updated to support newer NIPs.

Next Steps

• Add regression test for app_no=2 derivation path to prevent accidental changes.
• Investigate if app_no=128 (Hex) was the intended target for symmetric keys.