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exercism fetch crystal atbash-cipher

Atbash Cipher

Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.

The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards. The first letter is replaced with the last letter, the second with the second-last, and so on.

An Atbash cipher for the Latin alphabet would be as follows:

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Plain:  abcdefghijklmnopqrstuvwxyz
Cipher: zyxwvutsrqponmlkjihgfedcba

It is a very weak cipher because it only has one possible key, and it is a simple monoalphabetic substitution cipher. However, this may not have been an issue in the cipher's time.

Ciphertext is written out in groups of fixed length, the traditional group size being 5 letters, and punctuation is excluded. This is to make it harder to guess things based on word boundaries.

Examples

Setup

Follow the setup instructions for Crystal here:

http://exercism.io/languages/crystal

More help installing can be found here:

http://crystal-lang.org/docs/installation/index.html

Making the Test Suit Pass

Execute the tests with:

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$ crystal spec

In each test suite all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by changing pending to it.

Source

Wikipedia http://en.wikipedia.org/wiki/Atbash

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.