gistfile1.rb

#!/usr/bin/env ruby

require 'digest/sha1'
require 'io/console'

ALPHABET = ('0'..'9').to_a + ('a'..'z').to_a + ('A'..'Z').to_a

def hmac(key, msg)
  split_at = (key.length / 2).floor

  key1 = key[0, split_at]
  key2 = key[split_at..-1]

  hmac = Digest::SHA1.digest(key1 + Digest::SHA1.digest(key2 + msg))
  hmac.unpack('C*').map { |c| ALPHABET[c.modulo(ALPHABET.length)] }.join
end

def main
  print "Message: "
  msg = STDIN.gets.chomp

  print "Key: "
  STDIN.echo = false
  key = STDIN.gets.chomp
  STDIN.echo = true
  puts

  puts "Fingerprint: #{hmac(key,key)}"
  puts "HMAC: #{hmac(key, msg)}"
end

main