RedditUnstorage.rb

#!/usr/bin/env ruby

require 'openssl'

wordfile = ARGV.first || '/usr/share/dict/words'

ct = STDIN.read.unpack('m*').first
iv = ct[0..15]
ct = ct[16..-1]

cipher = OpenSSL::Cipher.new('AES-256-CBC')
digest = OpenSSL::Digest.new('sha256')
File.readlines(wordfile).map(&:chomp).each do |pw|
  cipher.decrypt
  cipher.key = digest.digest(pw)
  cipher.iv = iv
  cipher.padding = 0

  pt = cipher.update(ct) + cipher.final
  cipher.reset

  if pt =~ /\A[[:ascii:]]*\000*\z/
    puts "Password: #{pw}"
    puts "Plaintext: #{pt}"
    exit
  end
end