Bitcoin Taproot Implementation

[AIR-3][AIS-3][BPC-3][RES-3]

AI Labeling: This documentation is AI-generated with technical review and validation.

Last Updated: June 7, 2025

Overview

This document details the Taproot implementation in Anya Core, providing comprehensive coverage of BIP 341 (Taproot), BIP 342 (Tapscript), and related Bitcoin protocol enhancements.

Taproot Overview

Taproot is a Bitcoin protocol upgrade that improves privacy, scalability, and smart contract functionality through:

  • Schnorr Signatures (BIP 340): More efficient and private signature scheme
  • Taproot Outputs (BIP 341): Enhanced UTXO structure with script flexibility
  • Tapscript (BIP 342): Updated Bitcoin Script for Taproot transactions

Implementation Details

Core Taproot Support

use anya_core::bitcoin::taproot::{TaprootBuilder, TapLeaf, TapBranch};

// Create a Taproot output
let taproot_builder = TaprootBuilder::new();
let internal_key = generate_internal_key()?;

// Add script paths
let script = Script::new_v1_p2tr_unspendable();
let tap_leaf = TapLeaf::new(script, LeafVersion::TapScript)?;
taproot_builder.add_leaf(1, tap_leaf)?;

// Finalize Taproot tree
let taproot_info = taproot_builder.finalize(&secp, internal_key)?;
let output_key = taproot_info.output_key();

Schnorr Signature Implementation

use anya_core::bitcoin::crypto::schnorr::{Signature, Keypair};

// Generate Schnorr keypair
let keypair = Keypair::new(&secp, &mut rng);
let public_key = keypair.public_key();

// Sign message
let message = Message::from_slice(&hash)?;
let signature = keypair.sign_schnorr(message)?;

// Verify signature
assert!(signature.verify(&message, &public_key).is_ok());

Tapscript Operations

use anya_core::bitcoin::tapscript::{TapScript, Opcode};

// Create Tapscript
let tapscript = TapScript::builder()
    .push_opcode(Opcode::OP_DUP)
    .push_opcode(Opcode::OP_HASH160)
    .push_slice(&pubkey_hash)
    .push_opcode(Opcode::OP_EQUALVERIFY)
    .push_opcode(Opcode::OP_CHECKSIG)
    .into_script();

// Validate Tapscript
assert!(tapscript.is_tapscript_valid());

Transaction Structure

Taproot Transaction Input

use anya_core::bitcoin::transaction::{TxIn, TxOut, Transaction};

// Create Taproot input
let taproot_input = TxIn {
    previous_output: OutPoint::new(prev_txid, 0),
    script_sig: ScriptBuf::new(), // Empty for Taproot
    sequence: Sequence::ENABLE_RBF_NO_LOCKTIME,
    witness: Witness::new(), // Populated during signing
};

// Taproot witness structure
let witness = Witness::from_slice(&[
    signature.as_ref(),      // Signature
    control_block.serialize(), // Control block (for script path)
    script.as_bytes(),       // Script (for script path)
]);

Taproot Transaction Output

// Create Taproot output
let taproot_output = TxOut {
    value: Amount::from_sat(100000),
    script_pubkey: ScriptBuf::new_v1_p2tr_tweaked(output_key),
};

Key Management

Internal Key Generation

use anya_core::bitcoin::taproot::key::{InternalKey, TweakedKey};

// Generate internal key
let internal_key = InternalKey::new(&secp, &mut rng)?;

// Apply Taproot tweak
let merkle_root = compute_merkle_root(&tap_leaves)?;
let tweaked_key = internal_key.tap_tweak(&secp, merkle_root)?;
let output_key = tweaked_key.to_inner();

Key Path Spending

// Key path spending (most common case)
let key_spend_sig = sign_taproot_key_spend(
    &tweaked_keypair,
    &sighash,
    SigHashType::Default,
)?;

let witness = Witness::from_slice(&[key_spend_sig.as_ref()]);

Script Path Spending

// Script path spending
let script_spend_sig = sign_taproot_script_spend(
    &internal_keypair,
    &script,
    &sighash,
    SigHashType::Default,
)?;

let control_block = ControlBlock::new(
    LeafVersion::TapScript,
    internal_key.public_key(),
    merkle_proof,
)?;

let witness = Witness::from_slice(&[
    script_spend_sig.as_ref(),
    script.as_bytes(),
    control_block.serialize(),
]);

Advanced Features

Multi-Signature Taproot

use anya_core::bitcoin::taproot::musig::{MuSig2, AggregatePublicKey};

// MuSig2 aggregated signatures
let pubkeys = vec![pubkey1, pubkey2, pubkey3];
let agg_pubkey = AggregatePublicKey::new(&pubkeys)?;

// Create Taproot with aggregated key
let taproot_builder = TaprootBuilder::new();
let taproot_info = taproot_builder.finalize(&secp, agg_pubkey.inner())?;

Complex Script Trees

// Build complex Taproot tree
let taproot_builder = TaprootBuilder::new()
    .add_leaf(1, timeout_script)?
    .add_leaf(1, multisig_script)?
    .add_leaf(2, emergency_script)?
    .add_leaf(3, recovery_script)?;

let taproot_info = taproot_builder.finalize(&secp, internal_key)?;

Batch Validation

use anya_core::bitcoin::taproot::batch::{BatchValidator, TaprootItem};

// Batch validate multiple Taproot signatures
let mut batch_validator = BatchValidator::new();

for (signature, pubkey, message) in signatures.iter() {
    batch_validator.add_item(TaprootItem {
        signature: *signature,
        pubkey: *pubkey,
        message: *message,
    })?;
}

// Validate all signatures at once (more efficient)
assert!(batch_validator.verify(&secp)?);

Performance Optimizations

Signature Aggregation

// Aggregate multiple signatures for efficiency
let aggregated_sig = aggregate_signatures(&signatures)?;
let aggregated_pubkey = aggregate_public_keys(&pubkeys)?;

// Single verification for multiple signatures
assert!(aggregated_sig.verify(&message, &aggregated_pubkey).is_ok());

Pre-computed Tables

// Use pre-computed tables for faster operations
let precomputed_table = PrecomputedTable::new(&pubkey)?;
let signature = sign_with_precomputed(&keypair, &message, &precomputed_table)?;

Testing Framework

Unit Tests

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_taproot_key_spend() {
        let secp = Secp256k1::new();
        let keypair = Keypair::new(&secp, &mut rand::thread_rng());

        // Test key path spending
        let signature = sign_taproot_key_spend(&keypair, &sighash, SigHashType::Default)?;
        assert!(verify_taproot_signature(&signature, &pubkey, &message)?);
    }

    #[test]
    fn test_taproot_script_spend() {
        // Test script path spending
        let script = Script::new_p2pkh(&pubkey_hash);
        let tap_leaf = TapLeaf::new(script.clone(), LeafVersion::TapScript)?;

        // Verify script execution
        assert!(execute_tapscript(&script, &witness_stack)?);
    }
}

Integration Tests

#[tokio::test]
async fn test_taproot_transaction() {
    let bitcoin_client = BitcoinClient::new().await?;

    // Create and broadcast Taproot transaction
    let tx = create_taproot_transaction().await?;
    let txid = bitcoin_client.send_raw_transaction(&tx).await?;

    // Verify transaction in blockchain
    let confirmed_tx = bitcoin_client.get_transaction(&txid).await?;
    assert_eq!(confirmed_tx.txid(), txid);
}

Error Handling

Common Taproot Errors

use anya_core::bitcoin::taproot::error::TaprootError;

match taproot_operation() {
    Ok(result) => println!("Success: {:?}", result),
    Err(TaprootError::InvalidSignature) => {
        eprintln!("Invalid Taproot signature");
    }
    Err(TaprootError::InvalidControlBlock) => {
        eprintln!("Invalid control block");
    }
    Err(TaprootError::ScriptExecutionFailed) => {
        eprintln!("Tapscript execution failed");
    }
    Err(e) => eprintln!("Other error: {:?}", e),
}

Security Considerations

Best Practices

  1. Key Generation: Use cryptographically secure random number generators
  2. Signature Verification: Always verify signatures before processing
  3. Script Validation: Validate Tapscripts before execution
  4. Resource Limits: Implement proper resource limits for script execution

Vulnerability Prevention

// Prevent signature malleability
fn validate_signature_encoding(sig: &[u8]) -> Result<(), TaprootError> {
    if sig.len() != 64 {
        return Err(TaprootError::InvalidSignatureLength);
    }

    // Check for high S values (malleability)
    let s_bytes = &sig[32..];
    if is_high_s(s_bytes) {
        return Err(TaprootError::HighSSignature);
    }

    Ok(())
}

Compatibility

Bitcoin Core Compatibility

  • Compatible with Bitcoin Core 22.0+
  • Supports all Taproot-related RPCs
  • Full BIP 341/342 compliance

Network Support

  • Mainnet: Full Taproot support since block 709,632
  • Testnet: Full support for testing
  • Regtest: Complete support for development

Monitoring

Taproot Metrics

// Track Taproot usage metrics
let taproot_metrics = TaprootMetrics::new();
taproot_metrics.track_key_spend()?;
taproot_metrics.track_script_spend()?;
taproot_metrics.track_signature_verification_time(duration)?;

Performance Monitoring

// Monitor Taproot performance
let start = Instant::now();
let result = execute_taproot_operation()?;
let duration = start.elapsed();

metrics::histogram!("taproot_operation_duration", duration);

Resources

Documentation

Tools

Examples

This documentation follows the AI Labeling Standards based on official Bitcoin Improvement Proposals (BIPs).