cryptor.rb

require 'openssl'
require 'base64'

KEY_LENGTH = 2048
ENCRYPTION_KEY_LENGTH = 256
CIPHER_NAME = "aes-#{ENCRYPTION_KEY_LENGTH}-cfb"

class Hacker
  class << self
    attr_reader :public_key

    def generate_keys!
      @private_key = OpenSSL::PKey::RSA.new KEY_LENGTH
      @public_key = @private_key.public_key
    end

    def pay_money(encrypted_key)
      OpenSSL::PKey::RSA.new(@private_key).private_decrypt(encrypted_key)
    end
  end
end

class User
  attr_reader :data, :encrypted_key

  def initialize(data)
    @data = data
  end

  def encrypt!(public_key)
    # Encrypt data
    cipher = OpenSSL::Cipher.new(CIPHER_NAME).tap(&:encrypt)
    encryption_key = cipher.random_key + cipher.random_iv
    @data = cipher.update(data) + cipher.final

    # Encrypt key
    @encrypted_key = OpenSSL::PKey::RSA.new(public_key).public_encrypt(encryption_key)
  end

  def decrypt!(encryption_key)
    decipher = OpenSSL::Cipher.new(CIPHER_NAME).tap(&:decrypt)
    decipher.key, decipher.iv = encryption_key[0...32], encryption_key[32...48]
    @data = decipher.update(data) + decipher.final
  end
end

Hacker.generate_keys!

2.times do |i|
  data = "Data ##{i}!"

  user = User.new(data)
  user.encrypt!(Hacker.public_key)
  puts "Data encrypted? #{data != user.data}"
  decrypted_key = Hacker.pay_money(user.encrypted_key)
  user.decrypt!(decrypted_key)

  puts "Encryption key:\n#{Base64.encode64(decrypted_key)}"
  puts "Encrypted key:\n#{Base64.encode64(user.encrypted_key)}"
  puts "Data decrypted? #{data == user.data}"
  puts
end