archy/core/archipelago/src/seed.rs

//! BIP-39 master seed: generation, storage, and deterministic key derivation.
//!
//! One 24-word mnemonic derives ALL Archipelago keys:
//!
//!   BIP-39 Mnemonic (24 words, 256-bit entropy)
//!     → PBKDF2-HMAC-SHA512 (2048 rounds, empty passphrase)
//!     → Master Seed (64 bytes)
//!       ├── HKDF(seed, "archipelago/node/ed25519/v1")             → Node Ed25519 → did:key
//!       ├── HKDF(seed, "archipelago/nostr-node/secp256k1/v1")     → Node Nostr key
//!       ├── HKDF(seed, "archipelago/identity/{i}/ed25519/v1")     → Identity i Ed25519
//!       ├── BIP-32 m/44'/1237'/0'/0/{i}                           → Identity i Nostr (NIP-06)
//!       ├── BIP-32 m/84'/0'/0'                                    → Bitcoin Core wallet
//!       └── HKDF(seed, "archipelago/lnd/entropy/v1")              → LND aezeed entropy
//!
//! SECURITY: Never log mnemonic or seed material at any level.

use anyhow::{Context, Result};
use ed25519_dalek::SigningKey;
use hkdf::Hkdf;
use sha2::Sha256;
use zeroize::{Zeroize, ZeroizeOnDrop};

// ─── Constants ──────────────────────────────────────────────────────────

const SALT_LEN: usize = 16;
const NONCE_LEN: usize = 12;
const SEED_LEN: usize = 64;
const IDENTITY_INDEX_FILE: &str = "identity_index";
const ENCRYPTED_SEED_FILE: &str = "master_seed.enc";

// HKDF info strings for domain-separated key derivation.
const NODE_ED25519_INFO: &[u8] = b"archipelago/node/ed25519/v1";
const NODE_NOSTR_INFO: &[u8] = b"archipelago/nostr-node/secp256k1/v1";
const LND_ENTROPY_INFO: &[u8] = b"archipelago/lnd/entropy/v1";

// ─── MasterSeed ─────────────────────────────────────────────────────────

/// 64-byte master seed derived from a BIP-39 mnemonic.
/// Implements ZeroizeOnDrop to clear memory when dropped.
#[derive(Zeroize, ZeroizeOnDrop)]
pub struct MasterSeed {
    bytes: [u8; SEED_LEN],
}

impl MasterSeed {
    /// Generate a new 24-word BIP-39 mnemonic and derive the master seed.
    pub fn generate() -> Result<(bip39::Mnemonic, Self)> {
        let mnemonic = bip39::Mnemonic::generate(24)
            .map_err(|e| anyhow::anyhow!("Failed to generate mnemonic: {}", e))?;
        let seed = Self::from_mnemonic(&mnemonic);
        Ok((mnemonic, seed))
    }

    /// Derive master seed from an existing mnemonic (empty BIP-39 passphrase).
    pub fn from_mnemonic(mnemonic: &bip39::Mnemonic) -> Self {
        let seed_bytes = mnemonic.to_seed("");
        let mut bytes = [0u8; SEED_LEN];
        bytes.copy_from_slice(&seed_bytes);
        Self { bytes }
    }

    /// Parse a space-separated word string, validate checksum, and derive seed.
    pub fn from_mnemonic_words(words: &str) -> Result<(bip39::Mnemonic, Self)> {
        let mnemonic: bip39::Mnemonic = words.parse()
            .map_err(|e| anyhow::anyhow!("Invalid mnemonic: {}", e))?;
        let word_count = mnemonic.word_count();
        if word_count != 24 {
            anyhow::bail!("Expected 24 words, got {}", word_count);
        }
        let seed = Self::from_mnemonic(&mnemonic);
        Ok((mnemonic, seed))
    }

    /// Access raw seed bytes (for HKDF input).
    fn as_bytes(&self) -> &[u8; SEED_LEN] {
        &self.bytes
    }
}

// ─── Ed25519 Derivation (HKDF) ─────────────────────────────────────────

/// Derive the node's persistent Ed25519 signing key.
pub fn derive_node_ed25519(seed: &MasterSeed) -> Result<SigningKey> {
    let derived = hkdf_derive_32(seed.as_bytes(), NODE_ED25519_INFO)?;
    Ok(SigningKey::from_bytes(&derived))
}

/// Derive an identity's Ed25519 signing key by index.
pub fn derive_identity_ed25519(seed: &MasterSeed, index: u32) -> Result<SigningKey> {
    let info = format!("archipelago/identity/{}/ed25519/v1", index);
    let derived = hkdf_derive_32(seed.as_bytes(), info.as_bytes())?;
    Ok(SigningKey::from_bytes(&derived))
}

// ─── Secp256k1 / Nostr Derivation (BIP-32 + HKDF) ──────────────────────

/// Derive the node-level Nostr secp256k1 key (not per-identity).
pub fn derive_node_nostr_key(seed: &MasterSeed) -> Result<nostr_sdk::Keys> {
    let derived = hkdf_derive_32(seed.as_bytes(), NODE_NOSTR_INFO)?;
    let secret = nostr_sdk::SecretKey::from_slice(&derived)
        .map_err(|e| anyhow::anyhow!("Invalid secp256k1 key from HKDF: {}", e))?;
    Ok(nostr_sdk::Keys::new(secret))
}

/// Derive an identity's Nostr secp256k1 key via BIP-32.
/// Path: m/44'/1237'/0'/0/{index} (NIP-06 compliant).
pub fn derive_nostr_identity_key(seed: &MasterSeed, index: u32) -> Result<nostr_sdk::Keys> {
    use bitcoin::bip32::{ChildNumber, DerivationPath, Xpriv};
    use bitcoin::Network;

    let master = Xpriv::new_master(Network::Bitcoin, seed.as_bytes())
        .context("Failed to derive BIP-32 master key")?;

    let path = DerivationPath::from(vec![
        ChildNumber::from_hardened_idx(44).expect("valid"),
        ChildNumber::from_hardened_idx(1237).expect("valid"),
        ChildNumber::from_hardened_idx(0).expect("valid"),
        ChildNumber::from_normal_idx(0).expect("valid"),
        ChildNumber::from_normal_idx(index).expect("valid index"),
    ]);

    let secp = bitcoin::secp256k1::Secp256k1::new();
    let child = master.derive_priv(&secp, &path)
        .context("BIP-32 derivation failed")?;

    let secret_bytes = child.private_key.secret_bytes();
    let secret = nostr_sdk::SecretKey::from_slice(&secret_bytes)
        .map_err(|e| anyhow::anyhow!("Invalid Nostr key from BIP-32: {}", e))?;
    Ok(nostr_sdk::Keys::new(secret))
}

// ─── Bitcoin / LND Derivation ───────────────────────────────────────────

/// Derive the BIP-84 account-level extended private key for Bitcoin Core.
/// Path: m/84'/0'/0' (native segwit, mainnet).
pub fn derive_bitcoin_xprv(seed: &MasterSeed) -> Result<bitcoin::bip32::Xpriv> {
    use bitcoin::bip32::{ChildNumber, DerivationPath, Xpriv};
    use bitcoin::Network;

    let master = Xpriv::new_master(Network::Bitcoin, seed.as_bytes())
        .context("Failed to derive BIP-32 master key")?;

    let path = DerivationPath::from(vec![
        ChildNumber::from_hardened_idx(84).expect("valid"),
        ChildNumber::from_hardened_idx(0).expect("valid"),
        ChildNumber::from_hardened_idx(0).expect("valid"),
    ]);

    let secp = bitcoin::secp256k1::Secp256k1::new();
    master.derive_priv(&secp, &path)
        .context("BIP-84 derivation failed")
}

/// Derive 16 bytes of entropy for LND aezeed wallet initialization.
pub fn derive_lnd_entropy(seed: &MasterSeed) -> Result<[u8; 16]> {
    let derived = hkdf_derive(seed.as_bytes(), LND_ENTROPY_INFO, 16)?;
    let mut entropy = [0u8; 16];
    entropy.copy_from_slice(&derived);
    Ok(entropy)
}

// ─── Encrypted Seed Storage ─────────────────────────────────────────────

/// Encrypt and save the mnemonic words to disk (convenience backup).
/// Uses Argon2 key derivation + ChaCha20-Poly1305 AEAD.
pub async fn save_seed_encrypted(
    data_dir: &std::path::Path,
    mnemonic: &bip39::Mnemonic,
    passphrase: &str,
) -> Result<()> {
    use argon2::Argon2;
    use chacha20poly1305::aead::{Aead, KeyInit};
    use rand::RngCore;

    let identity_dir = data_dir.join("identity");
    tokio::fs::create_dir_all(&identity_dir).await
        .context("Failed to create identity directory")?;

    let plaintext = mnemonic.to_string();

    let mut salt = [0u8; SALT_LEN];
    let mut nonce = [0u8; NONCE_LEN];
    rand::rngs::OsRng.fill_bytes(&mut salt);
    rand::rngs::OsRng.fill_bytes(&mut nonce);

    let mut key = [0u8; 32];
    Argon2::default()
        .hash_password_into(passphrase.as_bytes(), &salt, &mut key)
        .map_err(|e| anyhow::anyhow!("Argon2 key derivation failed: {}", e))?;

    let cipher = chacha20poly1305::ChaCha20Poly1305::new_from_slice(&key)
        .map_err(|e| anyhow::anyhow!("Cipher init: {}", e))?;
    let ciphertext = cipher
        .encrypt(
            chacha20poly1305::aead::generic_array::GenericArray::from_slice(&nonce),
            plaintext.as_bytes(),
        )
        .map_err(|e| anyhow::anyhow!("Encryption failed: {}", e))?;

    // Zeroize the plaintext and key from memory.
    key.zeroize();

    // Format: salt || nonce || ciphertext
    let mut blob = Vec::with_capacity(SALT_LEN + NONCE_LEN + ciphertext.len());
    blob.extend_from_slice(&salt);
    blob.extend_from_slice(&nonce);
    blob.extend_from_slice(&ciphertext);

    let path = identity_dir.join(ENCRYPTED_SEED_FILE);
    tokio::fs::write(&path, &blob).await
        .context("Failed to write encrypted seed")?;

    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        tokio::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o600)).await
            .context("Failed to set seed file permissions")?;
    }

    Ok(())
}

/// Load and decrypt the mnemonic from disk.
pub async fn load_seed_encrypted(
    data_dir: &std::path::Path,
    passphrase: &str,
) -> Result<bip39::Mnemonic> {
    use argon2::Argon2;
    use chacha20poly1305::aead::{Aead, KeyInit};

    let path = data_dir.join("identity").join(ENCRYPTED_SEED_FILE);
    let blob = tokio::fs::read(&path).await
        .context("Failed to read encrypted seed file")?;

    if blob.len() < SALT_LEN + NONCE_LEN {
        anyhow::bail!("Encrypted seed file too short");
    }

    let salt = &blob[..SALT_LEN];
    let nonce = &blob[SALT_LEN..SALT_LEN + NONCE_LEN];
    let ciphertext = &blob[SALT_LEN + NONCE_LEN..];

    let mut key = [0u8; 32];
    Argon2::default()
        .hash_password_into(passphrase.as_bytes(), salt, &mut key)
        .map_err(|e| anyhow::anyhow!("Argon2 key derivation failed: {}", e))?;

    let cipher = chacha20poly1305::ChaCha20Poly1305::new_from_slice(&key)
        .map_err(|e| anyhow::anyhow!("Cipher init: {}", e))?;

    key.zeroize();

    let plaintext = cipher
        .decrypt(
            chacha20poly1305::aead::generic_array::GenericArray::from_slice(nonce),
            ciphertext,
        )
        .map_err(|_| anyhow::anyhow!("Decryption failed — wrong passphrase"))?;

    let words = String::from_utf8(plaintext)
        .context("Decrypted seed is not valid UTF-8")?;
    let mnemonic: bip39::Mnemonic = words.parse()
        .map_err(|e| anyhow::anyhow!("Decrypted data is not a valid mnemonic: {}", e))?;

    Ok(mnemonic)
}

/// Check if an encrypted seed file exists.
pub fn seed_exists(data_dir: &std::path::Path) -> bool {
    data_dir.join("identity").join(ENCRYPTED_SEED_FILE).exists()
}

// ─── Identity Index Tracking ────────────────────────────────────────────

/// Save the next unused identity derivation index.
pub async fn save_identity_index(data_dir: &std::path::Path, next_index: u32) -> Result<()> {
    let path = data_dir.join("identity").join(IDENTITY_INDEX_FILE);
    tokio::fs::write(&path, next_index.to_string().as_bytes()).await
        .context("Failed to write identity index")
}

/// Load the next unused identity derivation index (0 if none saved).
pub async fn load_identity_index(data_dir: &std::path::Path) -> Result<u32> {
    let path = data_dir.join("identity").join(IDENTITY_INDEX_FILE);
    match tokio::fs::read_to_string(&path).await {
        Ok(s) => s.trim().parse::<u32>().context("Invalid identity index"),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(0),
        Err(e) => Err(e).context("Failed to read identity index"),
    }
}

// ─── Internal Helpers ───────────────────────────────────────────────────

/// HKDF-SHA256 derivation with no salt, returns `len` bytes.
fn hkdf_derive(ikm: &[u8], info: &[u8], len: usize) -> Result<Vec<u8>> {
    let hk = Hkdf::<Sha256>::new(None, ikm);
    let mut okm = vec![0u8; len];
    hk.expand(info, &mut okm)
        .map_err(|_| anyhow::anyhow!("HKDF expand failed"))?;
    Ok(okm)
}

/// HKDF-SHA256 derivation with no salt, returns exactly 32 bytes.
fn hkdf_derive_32(ikm: &[u8], info: &[u8]) -> Result<[u8; 32]> {
    let bytes = hkdf_derive(ikm, info, 32)?;
    let mut out = [0u8; 32];
    out.copy_from_slice(&bytes);
    Ok(out)
}

// ─── Tests ──────────────────────────────────────────────────────────────

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

    const TEST_MNEMONIC: &str = "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art";

    #[test]
    fn test_deterministic_node_key() {
        let (_, seed1) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let (_, seed2) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let key1 = derive_node_ed25519(&seed1).unwrap();
        let key2 = derive_node_ed25519(&seed2).unwrap();
        assert_eq!(
            key1.verifying_key().as_bytes(),
            key2.verifying_key().as_bytes(),
            "Same mnemonic must produce same node key"
        );
    }

    #[test]
    fn test_deterministic_identity_keys() {
        let (_, seed) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let key_a = derive_identity_ed25519(&seed, 0).unwrap();
        let key_b = derive_identity_ed25519(&seed, 1).unwrap();
        assert_ne!(
            key_a.verifying_key().as_bytes(),
            key_b.verifying_key().as_bytes(),
            "Different indices must produce different keys"
        );

        // Same index is deterministic.
        let key_a2 = derive_identity_ed25519(&seed, 0).unwrap();
        assert_eq!(
            key_a.verifying_key().as_bytes(),
            key_a2.verifying_key().as_bytes(),
        );
    }

    #[test]
    fn test_node_key_differs_from_identity() {
        let (_, seed) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let node = derive_node_ed25519(&seed).unwrap();
        let identity = derive_identity_ed25519(&seed, 0).unwrap();
        assert_ne!(
            node.verifying_key().as_bytes(),
            identity.verifying_key().as_bytes(),
            "Node key and identity key must differ"
        );
    }

    #[test]
    fn test_deterministic_nostr_keys() {
        let (_, seed) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let keys1 = derive_nostr_identity_key(&seed, 0).unwrap();
        let keys2 = derive_nostr_identity_key(&seed, 0).unwrap();
        assert_eq!(
            keys1.public_key().to_hex(),
            keys2.public_key().to_hex(),
            "Same mnemonic + index must produce same Nostr key"
        );

        let keys3 = derive_nostr_identity_key(&seed, 1).unwrap();
        assert_ne!(
            keys1.public_key().to_hex(),
            keys3.public_key().to_hex(),
            "Different indices must produce different Nostr keys"
        );
    }

    #[test]
    fn test_node_nostr_key() {
        let (_, seed) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let keys1 = derive_node_nostr_key(&seed).unwrap();
        let keys2 = derive_node_nostr_key(&seed).unwrap();
        assert_eq!(keys1.public_key().to_hex(), keys2.public_key().to_hex());
    }

    #[test]
    fn test_bitcoin_xprv_deterministic() {
        let (_, seed) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let xprv1 = derive_bitcoin_xprv(&seed).unwrap();
        let xprv2 = derive_bitcoin_xprv(&seed).unwrap();
        assert_eq!(xprv1, xprv2);
    }

    #[test]
    fn test_lnd_entropy_deterministic() {
        let (_, seed) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();
        let e1 = derive_lnd_entropy(&seed).unwrap();
        let e2 = derive_lnd_entropy(&seed).unwrap();
        assert_eq!(e1, e2);
        assert_eq!(e1.len(), 16);
    }

    #[test]
    fn test_generate_produces_24_words() {
        let (mnemonic, _seed) = MasterSeed::generate().unwrap();
        assert_eq!(mnemonic.word_count(), 24);
    }

    #[test]
    fn test_invalid_mnemonic_rejected() {
        let result = MasterSeed::from_mnemonic_words("not a valid mnemonic");
        assert!(result.is_err());
    }

    #[test]
    fn test_wrong_word_count_rejected() {
        // 12 words (valid BIP-39 but we require 24)
        let result = MasterSeed::from_mnemonic_words(
            "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about"
        );
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_encrypted_storage_roundtrip() {
        let dir = tempfile::tempdir().unwrap();
        let (mnemonic, _seed) = MasterSeed::generate().unwrap();
        let words = mnemonic.to_string();

        save_seed_encrypted(dir.path(), &mnemonic, "test-passphrase").await.unwrap();
        assert!(seed_exists(dir.path()));

        let restored = load_seed_encrypted(dir.path(), "test-passphrase").await.unwrap();
        assert_eq!(restored.to_string(), words);
    }

    #[tokio::test]
    async fn test_encrypted_storage_wrong_passphrase() {
        let dir = tempfile::tempdir().unwrap();
        let (mnemonic, _seed) = MasterSeed::generate().unwrap();

        save_seed_encrypted(dir.path(), &mnemonic, "correct").await.unwrap();
        let result = load_seed_encrypted(dir.path(), "wrong").await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_identity_index_roundtrip() {
        let dir = tempfile::tempdir().unwrap();
        // Create identity subdirectory (required by the path).
        tokio::fs::create_dir_all(dir.path().join("identity")).await.unwrap();

        assert_eq!(load_identity_index(dir.path()).await.unwrap(), 0);
        save_identity_index(dir.path(), 5).await.unwrap();
        assert_eq!(load_identity_index(dir.path()).await.unwrap(), 5);
    }

    #[test]
    fn test_full_derivation_from_known_mnemonic() {
        // Verify all derivation paths produce valid, distinct keys from a known mnemonic.
        let (_, seed) = MasterSeed::from_mnemonic_words(TEST_MNEMONIC).unwrap();

        let node_ed = derive_node_ed25519(&seed).unwrap();
        let node_nostr = derive_node_nostr_key(&seed).unwrap();
        let id0_ed = derive_identity_ed25519(&seed, 0).unwrap();
        let id0_nostr = derive_nostr_identity_key(&seed, 0).unwrap();
        let _btc = derive_bitcoin_xprv(&seed).unwrap();
        let lnd = derive_lnd_entropy(&seed).unwrap();

        // All keys should be distinct (comparing hex representations).
        let node_ed_hex = hex::encode(node_ed.verifying_key().as_bytes());
        let id0_ed_hex = hex::encode(id0_ed.verifying_key().as_bytes());
        let node_nostr_hex = node_nostr.public_key().to_hex();
        let id0_nostr_hex = id0_nostr.public_key().to_hex();
        let lnd_hex = hex::encode(lnd);

        let all = [&node_ed_hex, &id0_ed_hex, &node_nostr_hex, &id0_nostr_hex, &lnd_hex];
        for (i, a) in all.iter().enumerate() {
            for (j, b) in all.iter().enumerate() {
                if i != j {
                    assert_ne!(a, b, "Keys at positions {} and {} should differ", i, j);
                }
            }
        }
    }
}