Scenario 7.2: Key Encapsulation (ML-KEM)

Questo scenario descrive la Key Encapsulation con ML-KEM (Module-Lattice-based Key Encapsulation Mechanism, NIST FIPS 203). ML-KEM è un meccanismo di Key Encapsulation (KEM) Post-Quantum, sicuro contro attacchi di computer quantistici.

KEM vs. Key Exchange:

using WvdS.Security.Cryptography.X509Certificates.Extensions.PQ;
 
using var ctx = PqCryptoContext.Initialize();
 
// Generare coppia di chiavi ML-KEM-768
using var mlKemKeyPair = ctx.GenerateKeyPair(PqAlgorithm.MlKem768);
 
// Esportare chiave pubblica (per il mittente)
var publicKeyPem = mlKemKeyPair.PublicKey.ToPem();
File.WriteAllText("recipient-mlkem.pub.pem", publicKeyPem);
 
// Salvare chiave privata cifrata
mlKemKeyPair.ToEncryptedPemFile("recipient-mlkem.key.pem", "SecurePassword!");
 
Console.WriteLine("Coppia chiavi ML-KEM-768 generata:");
Console.WriteLine($"  Chiave pubblica: {mlKemKeyPair.PublicKey.GetRawData().Length} Bytes");
Console.WriteLine($"  Algorithm OID: {mlKemKeyPair.PublicKey.Oid.Value}");

using var ctx = PqCryptoContext.Initialize();
 
// Caricare chiave pubblica destinatario
var recipientPublicKey = ctx.LoadPublicKey("recipient-mlkem.pub.pem");
 
// Eseguire Key Encapsulation
var (ciphertext, sharedSecret) = ctx.Encapsulate(recipientPublicKey);
 
Console.WriteLine($"Encapsulation completata:");
Console.WriteLine($"  Ciphertext: {ciphertext.Length} Bytes");
Console.WriteLine($"  Shared Secret: {sharedSecret.Length} Bytes");
Console.WriteLine($"  Shared Secret (hex): {Convert.ToHexString(sharedSecret)}");
 
// Inviare ciphertext al destinatario
File.WriteAllBytes("ciphertext.bin", ciphertext);
 
// Usare Shared Secret per cifratura
var encryptionKey = ctx.DeriveKey(
    sharedSecret,
    outputLength: 32,
    info: Encoding.UTF8.GetBytes("aes-encryption-key")
);

using var ctx = PqCryptoContext.Initialize();
 
// Caricare chiave privata
var privateKey = ctx.LoadPrivateKey("recipient-mlkem.key.pem", "SecurePassword!");
 
// Ricevere ciphertext
var ciphertext = File.ReadAllBytes("ciphertext.bin");
 
// Eseguire Decapsulation
var sharedSecret = ctx.Decapsulate(privateKey, ciphertext);
 
Console.WriteLine($"Decapsulation completata:");
Console.WriteLine($"  Shared Secret: {sharedSecret.Length} Bytes");
Console.WriteLine($"  Shared Secret (hex): {Convert.ToHexString(sharedSecret)}");
 
// Derivare stessa chiave del mittente
var decryptionKey = ctx.DeriveKey(
    sharedSecret,
    outputLength: 32,
    info: Encoding.UTF8.GetBytes("aes-encryption-key")
);

public class MlKemService
{
    private readonly PqCryptoContext _ctx;
 
    public MlKemService()
    {
        _ctx = PqCryptoContext.Initialize();
    }
 
    public (byte[] PublicKey, byte[] PrivateKey) GenerateKeyPair(MlKemParameterSet paramSet = MlKemParameterSet.MlKem768)
    {
        var algorithm = paramSet switch
        {
            MlKemParameterSet.MlKem512 => PqAlgorithm.MlKem512,
            MlKemParameterSet.MlKem768 => PqAlgorithm.MlKem768,
            MlKemParameterSet.MlKem1024 => PqAlgorithm.MlKem1024,
            _ => throw new ArgumentException("Set di parametri non valido")
        };
 
        using var keyPair = _ctx.GenerateKeyPair(algorithm);
        return (
            keyPair.PublicKey.GetRawData(),
            keyPair.PrivateKey.GetRawData()
        );
    }
 
    public (byte[] Ciphertext, byte[] SharedSecret) Encapsulate(byte[] publicKey)
    {
        using var pubKey = _ctx.ImportPublicKey(publicKey);
        return _ctx.Encapsulate(pubKey);
    }
 
    public byte[] Decapsulate(byte[] privateKey, byte[] ciphertext)
    {
        using var privKey = _ctx.ImportPrivateKey(privateKey);
        return _ctx.Decapsulate(privKey, ciphertext);
    }
}
 
public enum MlKemParameterSet
{
    MlKem512,
    MlKem768,
    MlKem1024
}

try
{
    var sharedSecret = ctx.Decapsulate(privateKey, ciphertext);
}
catch (CryptographicException ex) when (ex.Message.Contains("decapsulation"))
{
    // Decapsulation fallita - Ciphertext manipolato o chiave errata
    Console.WriteLine("Decapsulation fallita: Ciphertext non valido");
    throw new SecurityException("Verifica integrità fallita", ex);
}
catch (ArgumentException ex)
{
    // Formato errato
    Console.WriteLine($"Errore formato: {ex.Message}");
    throw;
}

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Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional