2d Caesar Cipher (chars)
Cryptogrpahy Video Eplainations
The Caesar Cipher
Programming a Caesar Cipher
shift = 3
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
'Complete' Cypher Program
class Main {
public static void main(String[] args) {
String message = "Hello World";
int offset=3;
StringBuilder result = new StringBuilder();
for (char character : message.toCharArray()) {
if (character != ' ') {
int originalAlphabetPosition = character - 'a';
int newAlphabetPosition = (originalAlphabetPosition + offset) % 26;
char newCharacter = (char) ('a' + newAlphabetPosition);
result.append(newCharacter);
} else {
result.append(character);
}
}
System.out.println(result);
}
}
🧪 Try the code out~!
Don't worrry about understanding the code yet! Since it goes over topics we didn't teach yet.
Exercise
- Try Changing the message.
- Try changing the offset
Breaking down the program
class Main {
public static void main(String[] args) {
char character = 'a';
int offset=4;
int originalAlphabetPosition = character - 'a';
int newAlphabetPosition = (originalAlphabetPosition + offset);
char newCharacter = (char) ('a' + newAlphabetPosition);
System.out.println(newCharacter);
}
}
🧪 Try the code out~!
Exercise
- Change Character from
aintobwhat do you think it should print? - Change offset from
4to2wha do you think it will be print?
But there is a bug!
- What happens if we write as letter z?
Fixing Our Minimalist Cipher
Here we have a simplified version of the program that only encodes one character.
Cypher
- Modular Explaination
class Main {
public static void main(String[] args) {
char character = 'h';
int offset=4;
int originalAlphabetPosition = character - 'a';
int newAlphabetPosition = (originalAlphabetPosition + offset) % 26;
char newCharacter = (char) ('a' + newAlphabetPosition);
System.out.println(newCharacter);
}
}
🧪 Try the code out~!
Assigment: Asking for User Input
The following program prompts the user to enter a character and encrypt it using the caesar cypher.
import java.util.*;
class Main {
public static void main(String[] args) {
System.out.print("Enter a Character : ");
Scanner sc = new Scanner(System.in);
char character = sc.nextLine().charAt(0);
int offset=4;
int originalAlphabetPosition = character - 'a';
int newAlphabetPosition = (originalAlphabetPosition + offset) % 26;
char newCharacter = (char) ('a' + newAlphabetPosition);
System.out.println(newCharacter);
}
}
Please fix this program
- So it asks what character to encrypt
- So that it also ask whats the offset of this.
More about cryptography
On the future
I don't think we will be going over those this semester, but hopefully I will be populating the "blog" section with more cryptography related problems and solutions as it is pretty relevant for Computer Science.