Wireless handheld devices are in use in several commercial applications including office buildings, universities and industrial plants. However, secure communication is one of the primary limitations of current commercial/military wireless networks. Current IEEE standards and solutions are inadequate as far as Information Assurance is concerned. Hence, the proposed authentication and key management solution is attractive for NASA as well as the private sector because it provides a unique methodology that ensures secure transmission of data between the nodes of any wireless network. It can be easily extended for mobile environments that include both wired and wireless segments based on varying commercial standards. With the availability of secure wireless access, organizations can provide wireless access to their servers outside their firewalls and buidings. In order to realize NASA's vision of Sensor-Web entailing a host of in-space and terrestrial communication links, enhanced network protocols and technologies are desired. Hence the developed authentication and data integrity methodology will be highly applicable to future NASA networks that would support secure communication among NASA spacecraft, commercial GEO networks and the ground systems. The proposed methodology will ensure authenticated data transfer between the public domain (Internet) and space-based networks. It will also satisfy the goals and objectives of NASA's Space Communications project, particularly for Proximity Wireless networks that aim to develop "energy-efficient, reliable, miniaturized, integrated wireless network technologies to enable robotic missions on planetary surfaces and in-space vehicles."