Question

Consider the encryption code  Encryption Code

true false - stringContains is an encryption algorithm that can be decrpyted
true false - Running reverseString twice will have no effect
true false - Running incLetters(s,4) then incLetters(s,-4) will have no effect
true false - using maxDigit as an encryption algorighm, it can be decrypted

USE CODE BELOW:

package encryption;
import java.util.Scanner;
public class Encryption {
    public static void main(String[] args) {
        Scanner scanner = new Scanner (System.in);
        String password, encryptedPassword, salt;
        int increment;
        System.out.print("Enter string to encrypt: ");  password = scanner.next();
        System.out.print("Enter encruption salt  : ");  salt     = scanner.next();
        increment = EncryptAlgos.maxDigit(salt);
        if (EncryptAlgos.stringContains(salt,"d")) { increment = increment * (-1); }
        encryptedPassword = EncryptAlgos.incLetters(password, increment);
        encryptedPassword = EncryptAlgos.reverseLetters(encryptedPassword);
        System.out.println("Encrypted string: " + encryptedPassword);
    }  
}
class EncryptAlgos {  // library of encryption algorityms
    public static String incLetters(String s, int amount) {
        String es = "";
        for(int i=0;i<s.length();i++) { es+=(char)(s.charAt(i)+amount); }
        return es;
    }
    public static String reverseLetters(String s) {
        String es = "";
        for(int i=s.length()-1;i >=0;i--) { es = es + s.charAt(i); }
        return es;
    }
    public static int maxDigit(String s) {
        int max = 1; int num;
        for(int i=0; i<s.length();i++) { 
            num = Character.getNumericValue(s.charAt(i));
            if (num > 0 && num < 10 && num > max) { max = num;}
        }
        return max;
    }
    public static boolean stringContains(String s, String c) {
        return s.contains(c);
    }    
}

Answer 1

stringContains is an encryption algorithm that can be decrpyted

False

Description: stringContains method only checks whether salt contains string "d" or not, it is not any encryption algorithm independently.

Running reverseString twice will have no effect

False

Description: If reverseString ran twice, the encryption string changes and it is not similar to when it ran once.

reverseString once:

Enter string to encrypt: abcd
Enter encruption salt : bcd
Encrypted string: cba`

reverseString twice:

Enter string to encrypt: abcd
Enter encruption salt : bcd
Encrypted string: `abc

Running incLetters(s,4) then incLetters(s,-4) will have no effect

False

Description: Running incLetters(s,4) then incLetters(s,-4) will give different results of encryption.

using maxDigit as an encryption algorighm, it can be decrypted

True

Description: using maxDigit as an encryption algorighm, it can be decrypted because it's logic is just to calculate maximum digit on loop.