The code breaker 🔐

The code breaker!

Let's talk about codes!

Back in the day, like waaaaay back in the day the Romans had a problem. Getting secret messages from a sender (fx a emporer) to a receiver (an commander) was difficult. If the enemy got hold of the message it could cost lives and even empires to fall. Therefore Julius Ceasar invented a way to encode a message so that other people could not just read the message in cleartext.

In this homework we will be working with how to decode and how to encode messages.

https://www.youtube.com/watch?v=Kf9KjCKmDcU

Number cypher

A number cypher takes a word and converts all charcters to numbers. The numbers are equal to the order of the character in the alphabeat. Here is an example:

Use the methods you created yesterday to solve the following problems!

Encoder

Create a method called numberCypherEncoder that takes a String and encodes that String

String benEncoded = numberCypherEncoder("ben");
System.out.println(benEncoded); // 2;5;14

String helloEncoded = numberCypherEncoder("hello");
System.out.println(helloEncoded); // 8;5;12;12;15

Decoder

Create a method called numberCypherDecoder that takes a String and encodes that String

String benEncoded = numberCypherEncoder("2;5;14");
System.out.println(benEncoded); // ben

String helloEncoded = numberCypherEncoder("8;5;12;12;15");
System.out.println(helloEncoded); // hello

Ceasar cypher

https://www.youtube.com/watch?v=sMOZf4GN3oc

https://www.youtube.com/watch?v=o6TPx1Co_wg

Encoder

Create a method called ceasarEncoder it takes a String and returns a new String with the encoded message. Here is an example of the output:

String helloEncodedCeasar = ceasarEncoder("hello");
System.out.println(helloEncodedCeasar); // khoor

Decoder

Create a method called ceasarDecoder it takes a String and returns a new String with the encoded message. Here is an example of the output:

String khoorDecodedCeasar = ceasarDecoder("khoor");
System.out.println(khoorDecodedCeasar); // hello

Test test test

Go here to test if your Ceasar cypher code works

Optional

Change the direction and the number of characters to shift!

Optimize the decoder and encoder functions so the direction and number of characters to shift can be put as arguments to the functions:

String helloEncodedCeasar = ceasarEncoder("hello", "left", 13);
String somewordDecodedCeasar = ceasarDecoder("someword", "left", 13);

Vigenère cipher - Advanced level optional

Skriv en decoder og en encoder for Vigenère cipher. Studer selv hvordan Vigenère cipher virker

Her er et eksempel på hvordan man ville bruge den:

String messageToEncode = "hello";
String key = "kea";
String helloEncodedVigenere = vigenereEncoder(messageToEncode, key);
System.out.println(helloEncodedVigenere); // rilvs

String messageToDecode = "rilvs";
String key = "kea";
String rilvsDecodedVigenere = vigenereDecoder(messageToDecode, key);
System.out.println(rilvsDecodedVigenere); // hello

Du kan teste om det du har skrevet virker med den her side: https://cryptii.com/pipes/vigenere-cipher

Enigma cypher - Expert level optional

Write an encoder and a decoder for the Enigma cypher.

Handin

Hand in on fronter here: https://kea-fronter.itslearning.com/LearningToolElement/ViewLearningToolElement.aspx?LearningToolElementId=929446

Hand in via git!

Handin checklist

• Have you tested that the code works?

• Have you written comments to the code?

• Have you thought of a good structure?

• Is the code easy to understand and read?

• Does the variablename make sense?