Appending a byte[] to the end of another byte[] [duplicate]

Using System.arraycopy(), something like the following should work:

// create a destination array that is the size of the two arraysbyte[] destination = new byte[ciphertext.length + mac.length];// copy ciphertext into start of destination (from pos 0, copy ciphertext.length bytes)System.arraycopy(ciphertext, 0, destination, 0, ciphertext.length);// copy mac into end of destination (from pos ciphertext.length, copy mac.length bytes)System.arraycopy(mac, 0, destination, ciphertext.length, mac.length);

Perhaps the easiest way:

ByteArrayOutputStream output = new ByteArrayOutputStream();output.write(ciphertext);output.write(mac);byte[] out = output.toByteArray();

You need to declare out as a byte array with a length equal to the lengths of ciphertext and mac added together, and then copy ciphertext over the beginning of out and mac over the end, using arraycopy.

byte[] concatenateByteArrays(byte[] a, byte[] b) {    byte[] result = new byte[a.length + b.length];     System.arraycopy(a, 0, result, 0, a.length);     System.arraycopy(b, 0, result, a.length, b.length);     return result;}