Prueba

import java.util.Scanner;

public class Main {

public static String decipher(String ciphertext, String knownWord) {
            String txt = ciphertext;
			String wrd = knownWord;
			char[] abc = new char[26];
			for ( int i=0 ; i < 26 ; i++) {
				abc[i] = (char) ('a' + i );
				//System.out.println(abc[i]);
			}
			for ( int i=0 ; i < txt.length() ; i++) {
				for (char c : abc) {
					if (c == txt.charAt(i)) {
						String nt = txt.replace("");
					}
				}
				//System.out.println(abc[i]);
			}
			
}

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    String ciphertext = scanner.nextLine();
    String knownWord = scanner.nextLine();

    String result = decipher(ciphertext, knownWord);
    System.out.println(result);
}

}