60 lines
1.6 KiB
Markdown
60 lines
1.6 KiB
Markdown
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# Atbash Cipher
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Welcome to Atbash Cipher on Exercism's Elixir Track.
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If you need help running the tests or submitting your code, check out `HELP.md`.
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## Instructions
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Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
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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.
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The first letter is replaced with the last letter, the second with the second-last, and so on.
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An Atbash cipher for the Latin alphabet would be as follows:
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```text
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Plain: abcdefghijklmnopqrstuvwxyz
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Cipher: zyxwvutsrqponmlkjihgfedcba
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```
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It is a very weak cipher because it only has one possible key, and it is a simple mono-alphabetic substitution cipher.
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However, this may not have been an issue in the cipher's time.
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Ciphertext is written out in groups of fixed length, the traditional group size being 5 letters, leaving numbers unchanged, and punctuation is excluded.
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This is to make it harder to guess things based on word boundaries.
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All text will be encoded as lowercase letters.
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## Examples
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- Encoding `test` gives `gvhg`
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- Encoding `x123 yes` gives `c123b vh`
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- Decoding `gvhg` gives `test`
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- Decoding `gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt` gives `thequickbrownfoxjumpsoverthelazydog`
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## Source
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### Created by
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- @rubysolo
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### Contributed to by
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- @andrewsardone
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- @angelikatyborska
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- @Br1ght0ne
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- @Cohen-Carlisle
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- @dalexj
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- @devonestes
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- @jinyeow
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- @kytrinyx
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- @lpil
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- @mhinz
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- @neenjaw
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- @parkerl
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- @sotojuan
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- @Teapane
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- @waiting-for-dev
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### Based on
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Wikipedia - https://en.wikipedia.org/wiki/Atbash
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