107 lines
3.7 KiB
Markdown
107 lines
3.7 KiB
Markdown
---
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title: "OTP: a Language-Agnostic Programming Challenge"
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date: 2015-01-26T00:00:00+00:00
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draft: false
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canonical_url: https://www.viget.com/articles/otp-a-language-agnostic-programming-challenge/
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---
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We spend our days writing Ruby and JavaScript (and love it), but we're
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always looking for what's next or just what's nerdy and interesting. We
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have folks exploring Rust, Go, D and Elixir, to name a few. I'm
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personally interested in strongly-typed functional languages like
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Haskell and OCaml, but I've had little success getting through their
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corresponding [animal books](http://www.oreilly.com/). I decided that if
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I was going to get serious about learning this stuff, I needed a real
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problem to solve.
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Inspired by an [online course on
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Cryptography](https://www.coursera.org/course/crypto), I specced out a
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simple [one-time pad](https://en.wikipedia.org/wiki/One-time_pad)
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encryptor/decryptor, [pushed it up to
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GitHub](https://github.com/vigetlabs/otp) and issued a challenge to the
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whole Viget dev team: write a pair of programs in your language of
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choice to encrypt and decrypt a message from the command line.
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## The Challenge
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When you [exclusive or](https://en.wikipedia.org/wiki/Exclusive_or)
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(XOR) a value by a second value, and then XOR the resulting value by the
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second value, you get the original value back. Suppose you and I want to
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exchange a secret message, the word "hi", and we've agreed on a secret
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key, the hexadecimal number `b33f` (or in binary, 1011 0011 0011 1111).
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**To encrypt:**
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1. Convert the plaintext ("hi") to its corresponding [ASCII
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values](https://en.wikipedia.org/wiki/ASCII#ASCII_printable_code_chart)
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("h" becomes 104 or 0110 1000, "i" 105 or 0110 1001).
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2. XOR the plaintext and the key:
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Plaintext: 0110 1000 0110 1001
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Key: 1011 0011 0011 1111
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XOR: 1101 1011 0101 0110
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3. Convert the result to hexadecimal:
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1101 = 13 = d
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1011 = 11 = b
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0101 = 5 = 5
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0110 = 6 = 6
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4. So the resulting ciphertext is "db56".
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**To decrypt:**
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1. Expand the ciphertext and key to their binary forms, and XOR:
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Ciphertext: 1101 1011 0101 0110
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Key: 1011 0011 0011 1111
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XOR: 0110 1000 0110 1001
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2. Convert the resulting binary numbers to their corresponding ASCII
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values:
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0110 1000 = 104 = h
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0110 1001 = 105 = i
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3. So, as expected, the resulting plaintext is "hi".
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The [Wikipedia](https://en.wikipedia.org/wiki/One-time_pad) page plus
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the [project's
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README](https://github.com/vigetlabs/otp#one-time-pad-otp) provide more
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detail. It's a simple problem conceptually, but in order to create a
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solution that passes the test suite, you'll need to figure out:
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- Creating a basic command-line executable
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- Reading from `STDIN` and `ARGV`
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- String manipulation
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- Bitwise operators
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- Converting to and from hexadecimal
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***
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As of today, we've created solutions in [~~eleven~~ ~~twelve~~ thirteen
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languages](https://github.com/vigetlabs/otp/tree/master/languages):
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- [C](https://viget.com/extend/otp-the-fun-and-frustration-of-c)
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- D
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- [Elixir](/elsewhere/otp-ocaml-haskell-elixir/)
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- Go
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- [Haskell](/elsewhere/otp-ocaml-haskell-elixir/)
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- JavaScript 5
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- JavaScript 6
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- Julia
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- [Matlab](https://viget.com/extend/otp-matlab-solution-in-one-or-two-lines)
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- [OCaml](/elsewhere/otp-ocaml-haskell-elixir/)
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- Ruby
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- Rust
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- Swift (thanks [wasnotrice](https://github.com/wasnotrice)!)
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The results are varied and fascinating -- stay tuned for future posts
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about some of our solutions. [In the
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meantime](https://www.youtube.com/watch?v=TDkhl-CgETg), we'd love to see
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how you approach the problem, whether in a new language or one we've
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already attempted. [Fork the repo](https://github.com/vigetlabs/otp) and
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show us what you've got!
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