A significant design parameter for secure embedded systems is the performance of the cryptographic algorithms implementation. We present a performance analysis on the same hardware of the cryptographic libraries available on the Google Android 2.2 and Microsoft Windows Phone 7 smartphone platforms and show that they exhibit quite different characteristics. This is an important consideration for designing multi-platform, security-aware applications. The use of cryptography requires mechanisms for handling the cryptographic keys. This is a hard-to-address and error-prone procedure, especially in systems with intermittent connectivity. The previously proposed Control Randomness Protocol (CRP) reduces the need for frequent key refreshing and extends the useful lifetime of a given set of keys. We present SCRP, an adaptation of the CRP for the smartphone environment. We show that SCRP achieves an adjustable security level in a fraction of computation and communication overhead.