Communication security measures are becoming prominent standards of next generation mobile networks. These measures usually involve resource-intensive cryptographic operations that can greatly affect communication performance, particularly when it comes to time-based guarantees such as delay and jitter. It this becomes vital to understand the computational characteristics of such operations from a communication perspective. The determination of these characteristics, however, is challenging with mobile computing as computational resources are dynamically managed for balanced performance and energy-efficiency. This paper investigates different mobile computing resource management features, and evaluates their impact on the evaluation of cryptographic functions used in message authentication, and on the design considerations for future context-aware security protocols.