How to generate secret key in Java once and use that key in 2 different programs

Question

My aim is to write a Java program to encrypt a text file (cipher text) using AES algorithm. And then, write another program to decrypt that encrypted file (cipher text) to get the plain text back. I want to use same key (same key, generate once, save it somewhere, and use it in both encryption and decryption program) for encryption and decryption process. If I generate key and do the encryption and decryption line by line in the same program then it works perfectly. Here is the working code snippet for that:

        String strDataToEncrypt = new String();
        String strCipherText = new String();
        String strDecryptedText = new String();

        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(128);
        SecretKey secretKey = keyGen.generateKey();

        Cipher aesCipher = Cipher.getInstance("AES");
        aesCipher.init(Cipher.ENCRYPT_MODE,secretKey);

        strDataToEncrypt = "any text input";
        byte[] byteDataToEncrypt = strDataToEncrypt.getBytes();
        byte[] byteCipherText = aesCipher.doFinal(byteDataToEncrypt); 
        strCipherText = new BASE64Encoder().encode(byteCipherText);
        System.out.println("cipher text: " +strCipherText);
        aesCipher.init(Cipher.DECRYPT_MODE,secretKey,aesCipher.getParameters());
        byte[] byteDecryptedText = aesCipher.doFinal(new BASE64Decoder().decodeBuffer(strCipherText));
        strDecryptedText = new String(byteDecryptedText);
        System.out.println("plain text again: " +strDecryptedText);

But, I need to have two different programs (java files) for encryption and decryption. So, I have to somehow generate a key and save that somewhere. Then use the same key for both encryption and decryption program. How can I do that?

EDIT_1

KeyGenerator keyGen = KeyGenerator.getInstance("AES");
keyGen.init(128);
SecretKey secretKey = keyGen.generateKey();
byte[] encoded = secretKey.getEncoded(); 
System.out.println("key: "+encoded);// key: [B@52b2a2d8

I can get the encoded key value using the above program. But my question is how to generate the SecretKey using this value in my decryption program?

Answer 1

Forgive me if I misunderstood your question but I believe you wish to reconstruct a SecretKey object from a existing key encoded in a byte array.

This can be performed simply by using the javax.crypto.spec.SecretKeySpec's constructor as such:

byte[] encoded = //Key data

SecretKey secretKey = new SecretKeySpec(encoded, "AES");

Since SecretKeySpec is a subclass of SecretKey no casting is needed. Should your encryption/decrption algorithm change please make sure to change the string literal used in the constructor AES to whatever algorithm you decided to use in the future.

Answer 2

Here's one way to print out the values in a byte[] array in hex:

byte[] a = {-120, 17, 42,121};
for (byte b : a)
{
    System.out.printf("%2X",b);
}
System.out.println();