secret = Digest::SHA1.hexdigest("yourpass")
a = ActiveSupport::MessageEncryptor.new(secret)
b = a.encrypt("eh")

c = ActiveSupport::MessageEncryptor.new(secret)
c.decrypt(b)

Read more: http://feeds.dzone.com/~r/dzone/snippets/~3/Z4RKXFix-HI/12535