public class Cryptage {

    public static String cryptage(String mdp) {

        String clé = "Interface";
        char c[] = new char[20];
        char m[] = new char[256];

        for (int i = 0; i < mdp.length();i++) {
            m[i] = mdp.charAt(i);
        }
        for (int i = 0; i < clé.length();i++) {
            c[i] = clé.charAt(i);
        }

        for (int i = 0; i<mdp.length();i++) {
            m[i] = (char) ((int)m[i] + (int)c[i%8]);
        }

        return String.valueOf(m).substring(0, mdp.length());

    }

}


public class Decryptage {

    public static String decryptage(String mdp) {

        String clé = "Interface";
        char c[] = new char[20];
        char m[] = new char[256];

        for (int i = 0; i < mdp.length();i++) {
            m[i] = mdp.charAt(i);
        }
        for (int i = 0; i < clé.length();i++) {
            c[i] = clé.charAt(i);
        }

        for (int i = 0; i<mdp.length();i++) {
            m[i] = (char) ((int)m[i] - (int)c[i%8]);
        }

        return String.valueOf(m);

    }

}