A mobile device sends a network attach request to a network node, and receives an authentication challenge from the network node, where the authentication challenge includes an authentication token, a random number, and a time variable associated with a current time at the network node. A microprocessor smart card of the mobile device retrieves the time variable from the authentication challenge, and starts a clock counter based on the retrieved time variable. The microprocessor smart card uses a current time represented by the clock counter to perform time expiration validation tests on certificates during Public Key Infrastructure (PKI) authentication or on authentication tokens during token-based authentication.