transaction.rs - Transactions

The transaction module defines the fundamental value transfer mechanism in Bunkercoin, implementing Ed25519 digital signatures with deterministic nonce generation and Blake3 hashing for radio-optimized financial operations.

Transaction Structure

// src/transaction.rs (lines 4-13)
#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct Transaction {
    pub sender: Vec<u8>,        // Ed25519 public key
    pub recipient: Vec<u8>,     // Ed25519 public key  
    pub amount: u64,            // Amount in base units
    pub nonce: u64,             // Deterministic nonce
    pub signature: Vec<u8>,     // Ed25519 signature
}

Ed25519 Cryptographic Implementation

Digital Signature Verification

// src/transaction.rs (lines 15-23)
impl Transaction {
    pub fn verify(&self) -> bool {
        let pk = PublicKey::from_bytes(&self.sender).unwrap();
        let data = self.data_to_sign();
        let sig_bytes: [u8; 64] = self.signature.clone().try_into().expect("sig length");
        let sig = Signature::from_bytes(&sig_bytes).unwrap();
        pk.verify(&data, &sig).is_ok()
    }
}

Signing Data Generation

// src/transaction.rs (lines 25-33)
fn data_to_sign(&self) -> Vec<u8> {
    let mut data = Vec::new();
    data.extend_from_slice(&self.sender);
    data.extend_from_slice(&self.recipient);
    data.extend_from_slice(&self.amount.to_le_bytes());
    data.extend_from_slice(&self.nonce.to_le_bytes());
    data
}

Ed25519 Advantages: Ed25519 provides 128-bit security equivalent with fast verification and small signature sizes (64 bytes), making it ideal for bandwidth-constrained radio transmissions while maintaining cryptographic strength.

Blake3 Transaction Hashing

// src/transaction.rs (lines 35-39)
pub fn hash(&self) -> [u8; 32] {
    let serialized = bincode::serialize(self).unwrap();
    blake3::hash(&serialized).into()
}

The Blake3 hash function provides:

• Deterministic hashing: Same transaction always produces same hash

• Collision resistance: Cryptographically secure transaction identification

• Fast computation: Optimized for low-power radio bridge environments

Deterministic Nonce System

Unlike Bitcoin's UTXO model, Bunkercoin uses a simplified account-based system with deterministic nonces:

Nonce Generation Strategy

// From wallet.rs - deterministic nonce calculation
let nonce = self.current_nonce; // Incremented for each transaction
self.current_nonce += 1;

Anti-Replay Protection

• Sequential nonces: Each transaction must have the next expected nonce

• State validation: Prevents double-spending through nonce verification

• Deterministic ordering: Ensures consistent transaction processing across nodes

Transaction Lifecycle

1. Creation and Signing

// Transaction creation pattern (from wallet.rs)
pub fn create_tx(&mut self, recipient: Vec<u8>, amount: u64) -> Transaction {
    let nonce = self.current_nonce;
    self.current_nonce += 1;
    
    let mut tx = Transaction {
        sender: self.public_key.to_bytes().to_vec(),
        recipient,
        amount,
        nonce,
        signature: Vec::new(),
    };
    
    let data = tx.data_to_sign();
    let signature = self.secret_key.sign(&data);
    tx.signature = signature.to_bytes().to_vec();
    tx
}

2. Network Propagation

• HTTP broadcast: POST /tx endpoint accepts individual transactions

• Mempool injection: Transactions stored pending block inclusion

• Peer synchronization: GET /mempool shares pending transactions

3. Block Inclusion

• Deterministic ordering: Transactions sorted by hash for consistent blocks

• Merkle root calculation: Blake3 hash of all transactions

• Finalization: Transactions become immutable once included in blocks

Radio-Optimized Features

Compact Binary Format

// Typical transaction size breakdown
struct TransactionSize {
    sender: [u8; 32],      // 32 bytes - Ed25519 public key
    recipient: [u8; 32],   // 32 bytes - Ed25519 public key
    amount: u64,           // 8 bytes  - Value transfer amount
    nonce: u64,            // 8 bytes  - Anti-replay protection
    signature: [u8; 64],   // 64 bytes - Ed25519 signature
}
// Total: 176 bytes per transaction

JS8Call Compatibility

• Single frame transmission: Most transactions fit in one 256-byte JS8Call frame

• Error detection: Built-in checksums enable corruption detection

• Human readable: JSON format allows manual verification during radio operations

Validation and Security

Cryptographic Validation Chain

// Complete transaction validation
fn validate_transaction(tx: &Transaction) -> Result<(), ValidationError> {
    // 1. Signature verification
    if !tx.verify() {
        return Err(ValidationError::InvalidSignature);
    }
    
    // 2. Public key format validation
    if tx.sender.len() != 32 || tx.recipient.len() != 32 {
        return Err(ValidationError::InvalidKeyFormat);
    }
    
    // 3. Amount validation
    if tx.amount == 0 {
        return Err(ValidationError::ZeroAmount);
    }
    
    // 4. Nonce validation (state-dependent)
    // Checked during mempool injection
    
    Ok(())
}

Security Properties

Property	Implementation	Purpose
Authentication	Ed25519 signature verification	Proves transaction authorization
Integrity	Blake3 hash validation	Detects transmission corruption
Non-repudiation	Immutable blockchain storage	Prevents transaction denial
Replay protection	Sequential nonce system	Prevents transaction reuse

Error Handling and Recovery

Malformed Transaction Handling

// Graceful error handling pattern
match Transaction::from_json(&received_data) {
    Ok(tx) => {
        if tx.verify() {
            blockchain.add_transaction(tx);
        } else {
            eprintln!("Invalid signature, discarding transaction");
        }
    }
    Err(e) => {
        eprintln!("Malformed transaction data: {}", e);
        // Continue processing other transactions
    }
}

Radio Transmission Errors

• Checksum validation: JSON deserialization detects corruption

• Signature verification: Cryptographic proof of integrity

• Graceful degradation: Invalid transactions discarded without affecting system

• Retransmission: Failed transactions can be rebroadcast by sender

Future Enhancements

Planned Transaction Features

• Multi-signature support: m-of-n signature schemes for enhanced security

• Smart contract integration: Programmable transaction conditions

• Privacy enhancements: Zero-knowledge proofs for transaction privacy

• UTXO migration: Transition to unspent transaction output model

Backward Compatibility

Transaction format extensions will maintain compatibility through:

• Version fields: Enable protocol upgrades

• Optional fields: New features added as optional extensions

• Legacy support: Older transaction formats remain valid