Rotational Cipher

Instructions

Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.

The Caesar cipher is a simple shift cipher that relies on transposing all the letters in the alphabet using an integer key between 0 and 26. Using a key of 0 or 26 will always yield the same output due to modular arithmetic. The letter is shifted for as many values as the value of the key.

The general notation for rotational ciphers is ROT + <key>. The most commonly used rotational cipher is ROT13.

A ROT13 on the Latin alphabet would be as follows:

Plain:  abcdefghijklmnopqrstuvwxyz
Cipher: nopqrstuvwxyzabcdefghijklm

It is stronger than the Atbash cipher because it has 27 possible keys, and 25 usable keys.

Ciphertext is written out in the same formatting as the input including spaces and punctuation.

Examples

• ROT5 omg gives trl
• ROT0 c gives c
• ROT26 Cool gives Cool
• ROT13 The quick brown fox jumps over the lazy dog. gives Gur dhvpx oebja sbk whzcf bire gur ynml qbt.
• ROT13 Gur dhvpx oebja sbk whzcf bire gur ynml qbt. gives The quick brown fox jumps over the lazy dog.

You need to implement the rotate function, which takes an Int and a String, and then encodes it using an rotational cipher. You can use the provided signature if you are unsure about the types, but don't let it restrict your creativity.

This exercise works with textual data. For historical reasons, Haskell's String type is synonymous with [Char], a list of characters. For more efficient handling of textual data, the Text type can be used.

As an optional extension to this exercise, you can

• read about string types in Haskell.
• add - text to your list of dependencies in package.yaml.
• import Data.Text in the following way:

import qualified Data.Text as T
import           Data.Text (Text)

• use the Text type e.g. rotate :: Int -> Text -> Text and refer to Data.Text combinators as e.g. T.pack.
• look up the documentation for Data.Text.
• replace all occurrences of String with Text in RotationalCipher.hs, i.e.:

rotate :: Int -> Text -> Text

This part is entirely optional.

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Source

Wikipedia