Technology evolution in wireless communication is enabling pervasive connectivity to Internet scale systems. In this scenario, security critical applications are being deployed over platforms which include mobile devices. It is thus key that security services be provided to mobile devices as well. Since security functions are typically based on computationally intensive cryptographic algorithms, achieving this goal is none of a simple task, for the following characteristics of mobile devices: 1) limited computing power, and 2) constraints imposed by peculiarities of the software platforms. This work presents an architecture which allows the provision of digital Time-Stamping services to mobile devices with limited resources. The architecture is described with respect to a case study system.