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We are working towards making exercises stand-alone. That is to say: no more generating READMEs on the fly. This will give maintainers more control over each individual exercise README, and it will also make some of the backend logic for delivering exercises simpler. The README template uses the Go text/template package, and the default templates generate the same READMEs as we have been generating on the fly. See the documentation in [regenerating exercise readmes][regenerate-docs] for details. The READMEs can be generated at any time using a new 'generate' command in configlet. This command has not yet landed in master or been released, but can be built from source in the generate-readmes branch on [configlet][]. [configlet]: https://github.com/exercism/configlet [regenerate-docs]: https://github.com/exercism/docs/blob/master/maintaining-a-track/regenerating-exercise-readmes.md
64 lines
1.8 KiB
Markdown
64 lines
1.8 KiB
Markdown
# Atbash Cipher
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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
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transposing all the letters in the alphabet such that the resulting
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alphabet is backwards. The first letter is replaced with the last
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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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```plain
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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
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a simple monoalphabetic substitution cipher. However, this may not have
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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
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being 5 letters, and punctuation is excluded. This is to make it harder to guess
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things based on word boundaries.
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## Examples
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- Encoding `test` gives `gvhg`
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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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## Elm Installation
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Refer to the [Exercism help page](http://exercism.io/languages/elm) for Elm
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installation and learning resources.
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## Writing the Code
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The first time you start an exercise, you'll need to ensure you have the
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appropriate dependencies installed.
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```bash
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$ npm install
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```
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Execute the tests with:
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```bash
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$ npm test
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```
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Automatically run tests again when you save changes:
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```bash
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$ npm run watch
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```
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As you work your way through the test suite, be sure to remove the `skip <|`
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calls from each test until you get them all passing!
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## Source
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Wikipedia [http://en.wikipedia.org/wiki/Atbash](http://en.wikipedia.org/wiki/Atbash)
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## Submitting Incomplete Solutions
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It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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