# Pay-to-Public-Key (P2PK) Example

This example demonstrates how to create and redeem Cashu tokens with Pay-to-Public-Key (P2PK) spending conditions. P2PK tokens are "locked" to a specific public key, meaning only the holder of the corresponding private key can spend them.

# What This Example Does

  1. Creates and funds a wallet with standard tokens
  2. Generates a secret key for P2PK conditions
  3. Creates P2PK-locked tokens that require a signature to spend
  4. Redeems the locked tokens using the private key
  5. Demonstrates the security model of locked tokens

# Key Concepts

  • P2PK (Pay-to-Public-Key): Tokens locked to a specific public key
  • Spending conditions: Rules that must be satisfied to spend tokens
  • Secret key generation: Creating cryptographic keys for token locking
  • Token redemption: Unlocking P2PK tokens with the correct private key

# Code Example

use std::sync::Arc;
use std::time::Duration;

use cdk::error::Error;
use cdk::nuts::{CurrencyUnit, SecretKey, SpendingConditions};
use cdk::wallet::{ReceiveOptions, SendOptions, Wallet};
use cdk::Amount;
use cdk_sqlite::wallet::memory;
use rand::random;
use tracing_subscriber::EnvFilter;

#[tokio::main]
async fn main() -> Result<(), Error> {
    let default_filter = "debug";

    let sqlx_filter = "sqlx=warn,hyper_util=warn,reqwest=warn,rustls=warn";

    let env_filter = EnvFilter::new(format!("{},{}", default_filter, sqlx_filter));

    // Parse input
    tracing_subscriber::fmt().with_env_filter(env_filter).init();

    // Initialize the memory store for the wallet
    let localstore = Arc::new(memory::empty().await?);

    // Generate a random seed for the wallet
    let seed = random::<[u8; 64]>();

    // Define the mint URL and currency unit
    let mint_url = "https://fake.thesimplekid.dev";
    let unit = CurrencyUnit::Sat;
    let amount = Amount::from(100);

    // Create a new wallet
    let wallet = Wallet::new(mint_url, unit, localstore, seed, None).unwrap();

    let quote = wallet.mint_quote(amount, None).await?;
    let proofs = wallet
        .wait_and_mint_quote(
            quote,
            Default::default(),
            Default::default(),
            Duration::from_secs(10),
        )
        .await?;

    // Mint the received amount
    println!(
        "Minted nuts: {:?}",
        proofs.into_iter().map(|p| p.amount).collect::<Vec<_>>()
    );

    // Generate a secret key for spending conditions
    let secret = SecretKey::generate();

    // Create spending conditions using the generated public key
    let spending_conditions = SpendingConditions::new_p2pk(secret.public_key(), None);

    // Get the total balance of the wallet
    let bal = wallet.total_balance().await?;
    println!("Total balance: {}", bal);

    // Send a token with the specified amount and spending conditions
    let prepared_send = wallet
        .prepare_send(
            10.into(),
            SendOptions {
                conditions: Some(spending_conditions),
                include_fee: true,
                ..Default::default()
            },
        )
        .await?;
    println!("Fee: {}", prepared_send.fee());
    let token = prepared_send.confirm(None).await?;

    println!("Created token locked to pubkey: {}", secret.public_key());
    println!("{}", token);

    // Receive the token using the secret key
    let amount = wallet
        .receive(
            &token.to_string(),
            ReceiveOptions {
                p2pk_signing_keys: vec![secret],
                ..Default::default()
            },
        )
        .await?;

    println!("Redeemed locked token worth: {}", u64::from(amount));

    Ok(())
}

# Dependencies

Add these dependencies to your Cargo.toml:

[dependencies]
cdk = { version = "*", default-features = false, features = ["wallet"] }
cdk-sqlite = { version = "*", features = ["wallet"] }
tokio = { version = "1", features = ["full"] }
rand = "0.8"
tracing = "0.1"
tracing-subscriber = { version = "0.3", features = ["env-filter"] }

# Running This Example

cargo run

# Expected Output

Minted nuts: [1, 2, 4, 8, 16, 32, 32, 4, 1]
Total balance: 100
Fee: 0
Created token locked to pubkey: 02a1b2c3d4e5f6... [public key]
cashuAeyJ0eXAiOiJib2x0MTEi... [P2PK token]
Redeemed locked token worth: 10

# Understanding P2PK Flow

# 1. Standard Token Creation

The example starts by minting regular Cashu tokens to have funds available.

# 2. Key Generation

let secret = SecretKey::generate();

This creates a new cryptographic key pair for the P2PK condition.

# 3. Spending Conditions

let spending_conditions = SpendingConditions::new_p2pk(secret.public_key(), None);

This creates a spending condition that requires a signature from the specific private key.

# 4. Locked Token Creation

The token is created with the P2PK spending condition, making it spendable only by the holder of the private key.

# 5. Token Redemption

let amount = wallet.receive(
    &token.to_string(),
    ReceiveOptions {
        p2pk_signing_keys: vec![secret],
        ..Default::default()
    },
).await?;

The token is redeemed by providing the correct private key.

# Use Cases for P2PK Tokens

# 1. Secure Payments

Send tokens that only the intended recipient can redeem:

// Create token locked to recipient's public key
let recipient_pubkey = get_recipient_pubkey();
let conditions = SpendingConditions::new_p2pk(recipient_pubkey, None);

# 2. Escrow Services

Create tokens that require specific signatures for release.

# 3. Multi-step Workflows

Lock tokens until certain conditions are met or verified.

# 4. Enhanced Privacy

Combine P2PK with other spending conditions for complex payment scenarios.

# Security Considerations

# Key Management

  • Secure storage: Private keys must be stored securely
  • Key backup: Losing the private key means losing access to the tokens
  • Key rotation: Consider using time-locked conditions for key rotation

# Token Validation

  • Public key verification: Always verify the public key before creating P2PK tokens
  • Signature validation: The wallet automatically validates signatures during redemption

# Advanced Features

# Time Locks

let lock_time = Some(unix_timestamp + 3600); // 1 hour from now
let conditions = SpendingConditions::new_p2pk(pubkey, lock_time);

# Multiple Signatures

You can create more complex spending conditions by combining P2PK with other conditions.

# Error Handling

Common errors include:

  • Missing private key: Attempting to redeem without the correct signing key
  • Invalid signature: Cryptographic signature validation failures
  • Expired tokens: Time-locked tokens accessed before the unlock time

# Next Steps

← BOLT12 Mint Token →