Wallet Core – PSBT & Raw Transaction Support

Overview

This project provides a UTXO-based wallet core with first-class PSBT (BIP-174) support, designed for both software and hardware wallet interoperability.

Key design goals:

• Clean separation between transaction construction, signing, and broadcasting
• Support for air-gapped / hardware wallet workflows
• Compatibility with Bitcoin-style UTXO chains (SegWit & legacy)
• Deterministic, inspectable, and auditable transactions

The wallet accepts either raw transaction hex or PSBT hex, making it flexible for advanced signing flows and external tools.

Features

• ✅ Raw transaction (hex) parsing & handling
• ✅ PSBT parsing, merging, and finalization
• ✅ Pre-sign inputs by default (configurable)
• ✅ Mixed signing support (partial + external)
• ✅ SegWit-aware size & fee handling
• ✅ Hardware-wallet-friendly architecture
• ✅ Clean Rust utility layer (utils.rs)

Input Formats

1. Raw Transaction Hex

Used when:

• The wallet controls all private keys
• Full signing is done internally
• No external signer is required

Example:

0200000001...

2. PSBT Hex (BIP-174)

Used when:

• Hardware wallets are involved
• Multi-sig or multi-party signing is required
• Offline or air-gapped signing is desired

Example:

70736274ff0100...

The wallet will:

• Detect PSBT automatically
• Pre-sign inputs it controls
• Leave remaining inputs untouched
• Allow merging and finalization later

Default Signing Behaviour

By default:

• Inputs controlled by the wallet are pre-signed
• External or unknown inputs remain unsigned
• Resulting PSBT can be:
  • Exported
  • Merged
  • Finalized
  • Converted to raw tx

This makes the wallet hardware-wallet safe by default.

Utility Functions

The wallet uses a small, auditable utility layer:

pub fn hex_to_bytes(s: &str) -> Vec<u8>
pub fn bytes_to_hex(b: &[u8]) -> String
pub fn u32_le(n: u32) -> [u8; 4]
pub fn u64_le(n: u64) -> [u8; 8]
pub fn varint(n: usize) -> Vec<u8>

These are used consistently across:

• Transaction serialization
• PSBT encoding/decoding
• Script and witness building

Hardware Wallet Compatibility

| Hardware Wallet | PSBT Support | SegWit | Notes | |-----------------|-------------|--------|-------| | Ledger (Nano S/X) | ✅ Yes | ✅ Yes | Requires Bitcoin app | | Trezor One | ✅ Yes | ⚠️ Partial | Limited SegWit v1 | | Trezor Model T | ✅ Yes | ✅ Yes | Full PSBT support | | Coldcard | ✅ Yes | ✅ Yes | Air-gapped PSBT workflow | | BitBox02 | ✅ Yes | ✅ Yes | Excellent PSBT UX | | Keystone | ✅ Yes | ✅ Yes | QR-based signing | | Passport | ✅ Yes | ✅ Yes | Air-gapped focused | | Jade | ✅ Yes | ✅ Yes | USB / QR signing |

Any device supporting BIP-174 PSBT will work with this wallet.

Typical Workflows

Software-Only Wallet

1. Build transaction
2. Sign all inputs
3. Broadcast raw hex

Hardware Wallet

1. Build PSBT
2. Pre-sign known inputs
3. Export PSBT
4. Sign on hardware wallet
5. Merge + finalize
6. Broadcast

Multi-Sig

1. Build base PSBT
2. Distribute to signers
3. Merge signatures
4. Finalize & broadcast

Security Notes

• No private keys are required for PSBT parsing
• Signing is isolated per input
• No hidden signing or mutation of external inputs
• Fully deterministic serialization

Status

🚧 Active Development
PSBT support is considered core infrastructure, not an add-on.

Upcoming:

• PSBT v2 (BIP-370)
• Descriptor-based wallets
• True vbyte fee calculation
• Advanced coin selection

License

MIT / Apache-2.0 (project dependent)