What is asynchronous generator?
An asynchronous password generator, has an authentication server
that generates a challenge (a large number or string) which is
encrypted with the private key of the token device and has that
token device's public key so it can verify authenticity of the
request (which is independent from the time factor). That challenge
can also include a hash of transmitted data, so not only can the
authentication be assured; but also the data integrity.