davideisinger.com/content/elsewhere/otp-a-language-agnostic-programming-challenge/index.md

title, date, draft, needs_review, canonical_url

title	date	draft	needs_review	canonical_url
OTP: a Language-Agnostic Programming Challenge	2015-01-26T00:00:00+00:00	false	true	https://www.viget.com/articles/otp-a-language-agnostic-programming-challenge/

We spend our days writing Ruby and JavaScript (and love it), but we're always looking for what's next or just what's nerdy and interesting. We have folks exploring Rust, Go, D and Elixir, to name a few. I'm personally interested in strongly-typed functional languages like Haskell and OCaml, but I've had little success getting through their corresponding animal books. I decided that if I was going to get serious about learning this stuff, I needed a real problem to solve.

Inspired by an online course on Cryptography, I specced out a simple one-time pad encryptor/decryptor, pushed it up to GitHub and issued a challenge to the whole Viget dev team: write a pair of programs in your language of choice to encrypt and decrypt a message from the command line.

The Challenge

When you exclusive or (XOR) a value by a second value, and then XOR the resulting value by the second value, you get the original value back. Suppose you and I want to exchange a secret message, the word "hi", and we've agreed on a secret key, the hexadecimal number b33f (or in binary, 1011 0011 0011 1111).

To encrypt:

1. Convert the plaintext ("hi") to its corresponding ASCII values ("h" becomes 104 or 0110 1000, "i" 105 or 0110 1001).

2. XOR the plaintext and the key:

   Plaintext: 0110 1000 0110 1001
   Key: 1011 0011 0011 1111
   XOR: 1101 1011 0101 0110
   

3. Convert the result to hexadecimal:

   1101 = 13 = d
   1011 = 11 = b
   0101 = 5 = 5
   0110 = 6 = 6
   

4. So the resulting ciphertext is "db56".

To decrypt:

1. Expand the ciphertext and key to their binary forms, and XOR:

   Ciphertext: 1101 1011 0101 0110
   Key: 1011 0011 0011 1111
   XOR: 0110 1000 0110 1001
   

2. Convert the resulting binary numbers to their corresponding ASCII values:

   0110 1000 = 104 = h
   0110 1001 = 105 = i
   

3. So, as expected, the resulting plaintext is "hi".

The Wikipedia page plus the project's README provide more detail. It's a simple problem conceptually, but in order to create a solution that passes the test suite, you'll need to figure out:

• Creating a basic command-line executable
• Reading from STDIN and ARGV
• String manipulation
• Bitwise operators
• Converting to and from hexadecimal

* * *

As of today, we've created solutions in eleven twelve thirteen languages:

• C
• D
• Elixir
• Go
• Haskell
• JavaScript 5
• JavaScript 6
• Julia
• Matlab
• OCaml
• Ruby
• Rust
• Swift (thanks wasnotrice!)

The results are varied and fascinating -- stay tuned for future posts about some of our solutions. In the meantime, we'd love to see how you approach the problem, whether in a new language or one we've already attempted. Fork the repo and show us what you've got!