McEliece (FlexiProvider): How can i create KeyPair from byte array?

Question

I use Flexi Provider (for McEliece algorithm) to generate my public and private keys and then i saved it to file and now i need to load keypair from file, i can read file and get public key byte array and private key byte array but i don`t know how can i create KeyPair from it: i use flexiprovider.de for McEliece Algorithm:

For Generating McEliece keys:

import de.flexiprovider.api.keys.KeySpec;
import de.flexiprovider.core.FlexiCoreProvider;
import de.flexiprovider.pqc.FlexiPQCProvider;
import de.flexiprovider.pqc.ecc.mceliece.McElieceKeyFactory;
import de.flexiprovider.pqc.ecc.mceliece.McElieceKeyPairGenerator;

public KeyPair generateKeyPair(){
    KeyPair kp = null;
    int KeySize = 256;
    Security.addProvider(new FlexiCoreProvider());
    Security.addProvider(new FlexiPQCProvider());

    try
    {

        McElieceKeyPairGenerator mcElieceKeyPairGenerator = new McElieceKeyPairGenerator();
        mcElieceKeyPairGenerator.initialize(KeySize, new SecureRandom());
        kp = mcElieceKeyPairGenerator.generateKeyPair();
    } catch (Exception e) {
        System.out.println(e.ToString());
    }
    return kp;
}

For Load KeyPair From Byte Array:

public KeyPair readKeyPair(byte[] privateKey, byte[] publicKey){
       //?? How can i create KeyPair
}

I try to use McElieceKeyFactory but i dont know how can i use it, It needs KeySpec (de.flexiprovider.api.keys.KeySpec) for generating Private Key and Public Key but de.flexiprovider.api.keys.KeySpec is abstract class and i can`t create new instance from it. so what should i do?

Edit 1: Saved method:

public void writeFile(byte[] data, String fileName) throws IOException{
    FileOutputStream out = new FileOutputStream(fileName);
    out.write(data);
    out.close();
}

public void saveKeyPair(KeyPair keyPair){
    byte[] privateKeyBytes = keyPair.getPrivate().getEncoded();
    byte[] publicKeyBytes = keyPair.getPublic().getEncoded();

    writeFile(privateKeyBytes,"Private.key");
    writeFile(publicKeyBytes,"Public.key");
}

Answer 1

Please try the following code. Also notice that I don't directly use the key pair generator and key factory implemetations.

KeyPairGenerator mcElieceKeyPairGenerator = KeyPairGenerator.getInstance("McEliece");
mcElieceKeyPairGenerator.initialize(keysize, new SecureRandom());
kp = mcElieceKeyPairGenerator.generateKeyPair();

final byte[] publicKeyData = kp.getPublic().getEncoded(); 
X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyData);
KeyFactory mcElieceKeyFactory = KeyFactory.getInstance("McEliece");
PublicKey regeneratedPublicKey = mcElieceKeyFactory.generatePublic(publicKeySpec);

final byte[] privateKeyData = kp.getPrivate().getEncoded();
PKCS8EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(privateKeyData);
PrivateKey regeneratedPrivateKey = mcElieceKeyFactory.generatePrivate(privateKeySpec);