Caesar Cipher Challenge

In cryptography, a Caesar cipher is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. The method is named after Julius Caesar, who used it in his private correspondence.

– Caesar cipher - Wikipedia, the free encyclopedia

We're going to implement a simple Caesar Cipher called ROT13 ("rotate by 13 places"). The transformation can be represented by aligning two alphabets:

Plain:    abcdefghijklmnopqrstuvwxyz
Cipher:   nopqrstuvwxyzabcdefghijklm

ROT13 is its own inverse; that is, to undo ROT13, the same algorithm is applied, so the same action can be used for encoding and decoding. The algorithm provides virtually no cryptographic security, and is often cited as a canonical example of weak encryption. ROT13 is used in online forums as a means of hiding spoilers, punchlines, puzzle solutions, and offensive materials from the casual glance.

Prerequisites

• None

Instructions

1. Fork and clone this repository.
2. Change into the new directory.
3. Install dependencies.
4. Create and checkout a new branch to work on.
5. Fulfill the listed requirements.

Starter code is available in the lib directory. A pull request is not required, but it is necessary if you want a code review.

You may wish to refer to FAQs related to forking, cloning.

Level 1

Please make a commit after completing each of the following steps.

1. #encode

Complete the definition of the encode method defined in challenge.rb. encode should take a single word as an argument and return encrypted text, as follows:

encode('hello') # => 'uryyb'
encode('world') # => 'jbeyq'

1. #decode

Next, complete the definition of the decode method. As you might expect, decode should be the inverse operation of encode. i.e.,

decode('uryyb') # => 'hello'
decode('jbeyq') # => 'world'

Hint: Take a look at this documentation -- there are a couple of predefined methods in each class/module that make this problem much simpler.

• Class: String
• Class: Array
• Module: Enumerable
• Class: Hash

Please run the Rubocop linter (rubocop lib) before debugging your code, since the linter will make it easy to spot many common sources of errors. After rubocop passes your code, run rspec to run the included tests, which will tell you whether or not your code meets the requirements.

Level 2

Do not attempt these until you have finished everything in Level 1! Make a commit after finishing each of these steps.

1. Spaces

Rewrite encode and decode so that they can operate on strings with spaces.

e.g.

encode('hello world') # => 'uryyb jbeyq'
decode('uryyb jbeyq') # => 'hello world'

1. Custom Rotation (aka Rot-n)

This one's a toughie! As you may have noticed, the method definitions of encode and decode have a second argument that they take, called rot. In the starter code, rot has been given a default value of 13. However, if you were to call either method with two inputs (e.g. encode('abc', 1)), rot would take the value of the second input.

Change encode and decode so that they rotate their messages by the value of rot, instead of always rotating by 13.

encode('abc', 1) # => 'bcd'
encode('abc def', 3) # => 'def ghi'
decode('def ghi', 3) # => 'abc def'
decode('bcd', 1) # => 'abc'

License

Source code distributed under the MIT license. Text and other assets copyright General Assembly, Inc., all rights reserved.