string.rb

# Extend String to include an encryption method
#
# For this to work, you must place this in the lib directory of your Rails project.
# You will also need three files in your config directory:
# * public.pem: Your public key file
# * private.pem: Your private key file
# * passphrase.txt: Your passphrase 
class String
  require 'openssl'
  require 'base64'

  def encrypt
    public_key_file = File.join(File.dirname(__FILE__), '..', 'config', 'public.pem')
    public_key = OpenSSL::PKey::RSA.new(File.read(public_key_file))

    Base64.encode64(public_key.public_encrypt(self))
  end

  def decrypt
    private_key_file = File.join(File.dirname(__FILE__), '..', 'config', 'private.pem')
    passphrase_file = File.join(File.dirname(__FILE__), '..', 'config', 'passphrase.txt')
    private_key = OpenSSL::PKey::RSA.new(File.read(private_key_file), File.read(passphrase_file).rstrip)

    private_key.private_decrypt(Base64.decode64(self))
  end
end