package edu.washington.cs.oneswarm.f2f.datagram;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;

import org.gudy.azureus2.core3.util.SHA1Hasher;

public abstract class DatagramEncrytionBase {
    public final static String ENCR_STD = "AES";
    public final static String ENCR_ALGO = "AES/CTR/PKCS5Padding";
    // public final static String HMAC_ALGO = "HmacSHA1";
    public static final int HMAC_SIZE = 20;

    // Using sha1 instead of hmac-sha1.
    public final static int HMAC_KEY_LENGTH = 20;
    public final static int AES_KEY_LENGTH = 128;
    public final static int BLOCK_SIZE = AES_KEY_LENGTH / 8;
    public final static int SEQUENCE_NUMBER_BYTES = 8;

    public static int TYPE_AES_CRT_128__SHA1 = 0;

    protected final SHA1Hasher sha1;

    public DatagramEncrytionBase() {
        sha1 = new SHA1Hasher();
    }

    public int getCryptoAlgo() {
        return TYPE_AES_CRT_128__SHA1;
    }

    protected byte[] hmac_key;

    protected IvParameterSpec ivSpec;
    protected Key key;
    protected Cipher cipher;

    protected static SecretKey createKeyForAES(int bitLength, SecureRandom random)
            throws NoSuchAlgorithmException, NoSuchProviderException {
        KeyGenerator generator = KeyGenerator.getInstance(ENCR_STD);
        generator.init(AES_KEY_LENGTH, random);
        return generator.generateKey();
    }

    protected static IvParameterSpec createCtrIvForAES(long sequenceNumber, SecureRandom random) {
        byte[] ivBytes = new byte[16];
        random.nextBytes(ivBytes);
        return setSequenceNumber(sequenceNumber, ivBytes);
    }

    protected static IvParameterSpec setSequenceNumber(long sequenceNumber, byte[] ivBytes) {
        ByteBuffer buf = ByteBuffer.wrap(ivBytes);
        buf.order(ByteOrder.BIG_ENDIAN); // Sun implements counter as
                                         // big-endian
        buf.position(8); // Counter is the last 8 bytes
        buf.putLong(sequenceNumber);
        return new IvParameterSpec(ivBytes);
    }

    protected static long getSequenceNumber(IvParameterSpec ivSpec) {
        ByteBuffer buf = ByteBuffer.wrap(ivSpec.getIV());
        buf.order(ByteOrder.BIG_ENDIAN); // Sun implements counter as
                                         // big-endian
        buf.position(8); // Counter is the last 8 bytes
        return buf.getLong();
    }
}