public static final byte[] xor(final byte[] x, final byte[] y) {
    if (x.length != y.length) {
      throw new IllegalArgumentException("The lengths of x and y should match.");
    }
    return xor(x, 0, y, 0, x.length);
  }
Computes the xor of two byte arrays of equal size.

@return a new byte[] of length x.length.
java_src/src/main/java/com/google/crypto/tink/subtle/Bytes.java