metamorphic-crypto

Zero-knowledge end-to-end encryption library with post-quantum hybrid KEM.

Built for Metamorphic and Mosslet — privacy-first apps by Moss Piglet Corporation where all user data is encrypted client-side and the server only stores opaque ciphertext.

What this provides

• Secretbox (XSalsa20-Poly1305) — symmetric authenticated encryption
• Sealed box (X25519) — anonymous public-key encryption (libsodium-compatible)
• Hybrid PQ KEM (ML-KEM-768 + X25519) — NIST Cat-3 post-quantum key encapsulation (default)
• Hybrid PQ KEM (ML-KEM-1024 + X25519) — NIST Cat-5 post-quantum key encapsulation (opt-in)
• Argon2id KDF — password-based key derivation (libsodium INTERACTIVE parameters)
• WASM bindings — browser-ready via wasm-pack
• Recovery keys — human-readable base32 encoding for key backup

Security levels

Both levels use the same combiner construction and X25519 classical fallback. hybrid_open auto-detects the level from the version tag byte — old and new ciphertext coexist seamlessly.

Security properties

• #![forbid(unsafe_code)] — no unsafe anywhere in the crate
• All secret key material zeroized after use
• Constant-time MAC comparison via RustCrypto
• OS CSPRNG via getrandom (no userspace PRNG)
• Hybrid construction: both ML-KEM AND X25519 must be broken to compromise a sealed key

Hybrid KEM construction

The hybrid combiner matches the format used by @noble/post-quantum's ml_kem768_x25519:

Seed expansion:  SHAKE256(seed_32) → 96 bytes [ML-KEM seed (64) || X25519 sk (32)]
Combiner:        SHA3-256(ss_mlkem || ss_x25519 || ct_x25519 || pk_x25519 || label)

Cat-3 (ML-KEM-768, default)

Public key:   ML-KEM-768 ek (1184 B) || X25519 pk (32 B) = 1216 bytes
Ciphertext:   0x02 || ML-KEM-768 ct (1088 B) || X25519 eph pk (32 B) || nonce (24 B) || secretbox ct

Cat-5 (ML-KEM-1024, opt-in)

Public key:   ML-KEM-1024 ek (1568 B) || X25519 pk (32 B) = 1600 bytes
Ciphertext:   0x03 || ML-KEM-1024 ct (1568 B) || X25519 eph pk (32 B) || nonce (24 B) || secretbox ct

Targets

Usage

use metamorphic_crypto::{generate_key, encrypt_secretbox_string, decrypt_secretbox_to_string};
use metamorphic_crypto::{generate_hybrid_keypair, hybrid_seal, hybrid_open};
use metamorphic_crypto::{generate_hybrid_keypair_1024, hybrid_seal_1024};

// Symmetric encryption
let key = generate_key();
let ciphertext = encrypt_secretbox_string("sensitive data", &key).unwrap();
let plaintext = decrypt_secretbox_to_string(&ciphertext, &key).unwrap();
assert_eq!(plaintext, "sensitive data");

// Hybrid PQ seal (Cat-3, default)
let kp = generate_hybrid_keypair();
let sealed = hybrid_seal(b"context_key_bytes", &kp.public_key).unwrap();
let opened = hybrid_open(&sealed, &kp.secret_key).unwrap();

// Hybrid PQ seal (Cat-5)
let kp5 = generate_hybrid_keypair_1024();
let sealed5 = hybrid_seal_1024(b"context_key_bytes", &kp5.public_key).unwrap();
let opened5 = hybrid_open(&sealed5, &kp5.secret_key).unwrap(); // auto-detects level

WASM (browser)

wasm-pack build --target web --release

import init, { deriveSessionKey, encryptSecretboxString } from './pkg/metamorphic_crypto.js';

await init('/path/to/metamorphic_crypto_bg.wasm');

const key = deriveSessionKey(password, saltBase64);
const ciphertext = encryptSecretboxString("hello", key);

Tests

cargo test          # unit + integration + cross-level compatibility
cargo clippy        # zero warnings
cargo fmt --check   # formatted

License

Dual-licensed under MIT or Apache-2.0 at your option.