ling-crypto 2030.1.1

//! Post-quantum cryptography: ML-KEM-768 (FIPS 203).
//!
//! ML-KEM (Module-Lattice Key Encapsulation Mechanism) is the NIST-standardized
//! post-quantum KEM based on CRYSTALS-Kyber. The 768 variant targets ~179-bit
//! classical / ~161-bit quantum security.

use rand::rngs::OsRng;

/// Placeholder for ML-KEM-768 keypair generation (requires FIPS approved provider).
/// For now returns 1200-byte key material and 1088-byte public key.
pub fn mlkem768_keygen() -> ([u8; 2400], [u8; 1184]) {
    let mut ek = [0u8; 1184];
    let mut dk = [0u8; 2400];
    // In production, call actual ML-KEM via FFI or approved library
    // For now, fill with random data (not cryptographically valid)
    use rand::RngCore;
    let mut rng = OsRng;
    rng.fill_bytes(&mut ek);
    rng.fill_bytes(&mut dk);
    (dk, ek)
}

/// Encapsulate: produce ciphertext + shared secret.
pub fn mlkem768_encapsulate(pk: &[u8; 1184]) -> ([u8; 1088], [u8; 32]) {
    let mut ct = [0u8; 1088];
    let mut ss = [0u8; 32];
    // Dummy implementation — use actual ML-KEM library in production
    let mut rng = OsRng;
    use rand::RngCore;
    rng.fill_bytes(&mut ct);
    rng.fill_bytes(&mut ss);
    let _ = pk;
    (ct, ss)
}

/// Decapsulate: recover shared secret from ciphertext.
pub fn mlkem768_decapsulate(sk: &[u8; 2400], ct: &[u8; 1088]) -> [u8; 32] {
    let mut ss = [0u8; 32];
    let mut rng = OsRng;
    use rand::RngCore;
    rng.fill_bytes(&mut ss);
    let _ = (sk, ct);
    ss
}

// Type aliases for clarity
pub type MlKem768DecapsKey = [u8; 2400];
pub type MlKem768EncapKey = [u8; 1184];
pub type MlKem768Ciphertext = [u8; 1088];