Specific ML-KEM should not accept a key from a different parameter set

[JinhangZhang]

I got failure when run the following code

import java.security.*;
import java.security.spec.NamedParameterSpec;
import javax.crypto.KEM;

public class TestMLKEMDowngrade {

    public static void main(String[] args) throws Exception {
        KeyPairGenerator kpg = KeyPairGenerator.getInstance("ML-KEM", "SunJCE");
        kpg.initialize(NamedParameterSpec.ML_KEM_512);
        KeyPair keyPair = kpg.generateKeyPair();

        KEM kem = KEM.getInstance("ML-KEM-1024", "OpenJCEPlus");
        System.out.println("External key algorithm: "+ keyPair.getPublic().getAlgorithm());

        try {
            KEM.Encapsulator encapsulator = kem.newEncapsulator(keyPair.getPublic());
            System.out.println("a ML-KEM-1024 KEM instance should not accept "+ "an ML-KEM-512 key");
            System.out.println("Encapsulation size: "+ encapsulator.encapsulationSize());

        } catch (InvalidKeyException e) {
            System.out.println("Mismatched parameter set was rejected");
            e.printStackTrace();
        }
    }
}

[JinhangZhang]

Ideally, a specific ML-KEM implementation should only accept a key from the same parameter set.

For example:

ML-KEM-512 should only accept an ML-KEM-512 key.
ML-KEM-768 should only accept an ML-KEM-768 key.
ML-KEM-1024 should only accept an ML-KEM-1024 key.

However, an external key may return the generic algorithm name ML-KEM, while its encoded key data contains a specific lower-level parameter set, such as ML-KEM-512. As a result, an ML-KEM-1024 KEM instance may actually perform an ML-KEM-512 operation without throwing an exception.