Nov 18

The following code can be used to convert a byte array (containing the bytes of a long) into a long.

	public static long byteArrayToLong(byte[] bytes) {
		long l = 0;
		for (int i=0; i<8; i++) {
			l <<= 8;
			l ^= (long) bytes[i] & 0xff;
		}
		return l;
	}

This is the reverse of “How to convert a long to a byte array“.

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Jul 17

Once you have generated a SecretKey you can use it’s getEncoded() method to generate a byte array that can be used to recreate the key.


        // Use the following to initially create a random key

        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        kgen.init(256);
        SecretKey key = keyGen.generateKey();

        // Then use the following to get the 

        byte[] encoded = key.getEncoded();

        // byte array could now be saved for later use to recreate key

To then recreate your key using the byte array, you can use the following:

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

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May 16

The following code can be used to extract the 8 bytes from a long value and return them as a byte array

public static byte[] longToByteArray(long data) {
    return new byte[] {
        (byte)((data >> 56) & 0xff),
        (byte)((data >> 48) & 0xff),
        (byte)((data >> 40) & 0xff),
        (byte)((data >> 32) & 0xff),
        (byte)((data >> 24) & 0xff),
        (byte)((data >> 16) & 0xff),
        (byte)((data >> 8 ) & 0xff),
        (byte)((data >> 0) & 0xff),
    };
}

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