kry-ctr-spn/src/main/java/ch/fhnw/kry/SPN.java

package ch.fhnw.kry;

public class SPN {
    private final static int ROUND_KEY_LENGTH = 16;

    public int k(int key, int i) {
        i *= 4;
        int mask = 0xFFFF_0000 >>> i;

        return key & mask >>> ROUND_KEY_LENGTH - i;
    }
}