crypt example

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.util.Timer;
import java.util.TimerTask;
import java.util.Base64;

public class Bunnies {

    public static final long msecsIn24Hours = 86400000L;

    public static final int CS_256_SHA_AES_CTR = 1;

    public static SecureRandom sRand = new SecureRandom();
    static {
        new Timer("re-seed", true).scheduleAtFixedRate(new TimerTask(){
            @Override
            public void run() {
                sRand = new SecureRandom();
            }
        }, msecsIn24Hours, msecsIn24Hours);
    }

    public static String decrypt(byte [] rawInput, byte [] srpKey, int cipherSuite) {

        if (cipherSuite != CS_256_SHA_AES_CTR) {
            throw new IllegalArgumentException("Unsupported cipher suite : " + cipherSuite);
        }

        try {

            MessageDigest md = MessageDigest.getInstance("SHA-256");
            // $TODO: note that aesKey can be pre-calculated before, and
            // provided as parameter to this method, to avoid unnecessary hashing
            byte[] aesKey = md.digest(srpKey);
            Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");

            int blkSize = cipher.getBlockSize();

            if (rawInput.length <= blkSize) {
                throw new IllegalArgumentException("Too little data");
            }

            cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(aesKey, "AES"),
                    new IvParameterSpec(rawInput, 0, blkSize));

            return new String(cipher.doFinal(rawInput, blkSize, rawInput.length - blkSize), "UTF-8");

        } catch (RuntimeException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }

    }


    public static byte [] encrypt(Object rawInput, byte [] srpKey, int cipherSuite) {

        if (cipherSuite != CS_256_SHA_AES_CTR) {
            throw new IllegalArgumentException("Unsupported cipher suite : " + cipherSuite);
        }

        try {

            MessageDigest md = MessageDigest.getInstance("SHA-256");
            // $TODO: note that aesKey can be pre-calculated before, and
            // provided as parameter to this method, to avoid unnecessary hashing
            byte[] aesKey = md.digest(srpKey);
            // aesKey = new byte[]{0x2b,0x7e,0x15,0x16,0x28,(byte)0xae,(byte)0xd2,(byte)0xa6,(byte)0xab,(byte)0xf7,0x15,(byte)0x88,0x9,(byte)0xcf,0x4f,0x3c};
            Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");

            int blkSize = cipher.getBlockSize();

            byte [] iv = new byte[blkSize];
            // iv = new byte[]{-16,-15,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1};
            sRand.nextBytes(iv);

            cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(aesKey, "AES"),
                    new IvParameterSpec(iv));

            byte [] rawBytes;
           if (rawInput instanceof String) {
               rawBytes = ((String)rawInput).getBytes();
           } else {
               rawBytes = (byte[])rawInput;
           }
            byte [] bits = cipher.doFinal(rawBytes);
            byte [] total = new byte[iv.length + bits.length];

            System.arraycopy(iv, 0, total, 0, blkSize);
            System.arraycopy(bits, 0, total, blkSize, bits.length);
            return total;

        } catch (RuntimeException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }

    }

    public static void main(String a[]) {

        byte [] srpKey = new byte[]{1,2,3,4};
        if ("d".equals(a[0])) {
            byte [] input = Base64.getDecoder().decode(a[1]);
            System.out.println(decrypt(input, srpKey, CS_256_SHA_AES_CTR));
        } else if ("e".equals(a[0])) {
            System.out.println(Base64.getEncoder().encodeToString(encrypt(a[1], srpKey, CS_256_SHA_AES_CTR)));
        } else if ("s".equals(a[0])) {
            System.out.println(Base64.getEncoder().encodeToString(encrypt(new byte[]{0x6b,(byte)0xc1,(byte)0xbe,(byte)0xe2,0x2e,0x40,(byte)0x9f,(byte)0x96,(byte)0xe9,0x3d,0x7e,0x11,0x73,(byte)0x93,0x17,0x2a}, srpKey, CS_256_SHA_AES_CTR)));
        }

    }

}