TANOS: Taproot Adaptor for Nostr-Orchestrated Swaps

TANOS is a library implementing atomic swaps between Bitcoin and Nostr, using Taproot and Schnorr adaptor signatures, developed for the MIT Bitcoin Hackathon.

Overview

TANOS allows atomic swaps between: - Bitcoin transactions using Taproot P2TR addresses - Nostr events with Schnorr signatures

The protocol uses adaptor signatures to ensure atomicity: the buyer only gets the signed Nostr event if they pay with Bitcoin, and the seller only gets the Bitcoin if they reveal the secret from the Nostr signature.

Inspiration

This project is inspired by NIP 455: Atomic Signature Swaps, which proposes a standard for performing atomic swaps of cryptographic signatures over Nostr.

Features

• BIP340-compliant Schnorr adaptor signatures
• Taproot address creation and transaction handling
• Nostr event creation and signing
• Complete atomic swap protocol implementation
• Pure Go implementation

Project Structure

The project is organized into the following packages:

• pkg/adaptor - Adaptor signature implementation using Schnorr
• pkg/bitcoin - Bitcoin-related functionality (Taproot, transactions)
• pkg/crypto - Common cryptographic utilities
• pkg/nostr - Nostr-related functionality
• pkg/tanos - High-level swap protocol implementation
• examples/swap - Example implementation of a complete swap

Getting Started

Prerequisites

• Go 1.24.1 or later
• Bitcoin and Nostr dependencies

Installation

git clone https://github.com/GustavoStingelin/tanos.git
cd tanos
go mod download

Running the Example

go run examples/swap/main.go

The Swap Protocol

1. Setup:
2. Seller has a Nostr private key

3. Buyer has Bitcoin

4. Commitment:

5. Seller creates and signs a Nostr event
6. Seller extracts the nonce (R) from the signature

7. Seller computes the commitment T = R + e*P

8. Locking:

9. Buyer creates a Bitcoin transaction locking funds to a P2TR address
10. Buyer creates an adaptor signature using the commitment T

11. Buyer sends the adaptor signature to the seller

12. Revealing:

13. Seller completes the adaptor signature using the secret from the Nostr signature

14. Seller broadcasts the Bitcoin transaction with the completed signature

15. Verification:

16. Buyer extracts the secret from the completed signature
17. Buyer verifies that the secret matches the one in the Nostr signature

Security Considerations

BIP340 Parity Rules

TANOS carefully implements BIP340 parity rules for Schnorr signatures. According to the specification:

• Schnorr signatures in BIP340 require the Y-coordinate of the nonce point (R) to be even
• When the Y-coordinate is odd, the signature value 's' must be negated
• This affects how secrets are extracted from completed signatures

This implementation automatically handles these parity adjustments, ensuring that: 1. Generated Bitcoin signatures are valid according to BIP340 2. Secrets extracted from signatures are correctly recovered, even after parity adjustments

Tagged Hashes

For enhanced security, the library uses BIP340-style tagged hashes for all signature challenges, ensuring signatures from different contexts cannot be reused.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• BIP340 (Schnorr Signatures)
• BIP341 (Taproot)
• Nostr Protocol
• MIT Bitcoin Hackathon
• NIP 455: Atomic Signature Swaps