Перевести метод с Ruby на Java

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.SecureRandom;
import java.security.Signature;
    //@param : extenstionContents  is your zip file , 
    //@returns :  byte[] of the signature , use ByteBuffer to merge them and you have your   
    // .crx
    public static byte[] generateCrxHeader(byte[] extensionContents) throws Exception {
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");      
        SecureRandom random = new SecureRandom();
        keyGen.initialize(1024, random);        
 
        KeyPair pair = keyGen.generateKeyPair();
 
        Signature sigInstance = Signature.getInstance("SHA1withRSA");
        sigInstance.initSign(pair.getPrivate());
        sigInstance.update(extensionContents);
        byte [] signature = sigInstance.sign();
        byte [] subjectPublicKeyInfo = pair.getPublic().getEncoded();
        final int headerLength = 4 + 4 + 4 + 4 + subjectPublicKeyInfo.length + signature.length;
        ByteBuffer headerBuf = ByteBuffer.allocate(headerLength);
        headerBuf.order(ByteOrder.LITTLE_ENDIAN);
        headerBuf.put(new byte[]{0x43,0x72,0x32,0x34}); // Magic number
        headerBuf.putInt(2); // Version
        headerBuf.putInt(subjectPublicKeyInfo.length); // public key length
        headerBuf.putInt(signature.length); // signature length
        headerBuf.put(subjectPublicKeyInfo);
        headerBuf.put(signature);
        final byte [] header = headerBuf.array();
        return header;
    }