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Equipping Medical Electronic Devices with FIPS-140-2 Compliant Wi-Fi

The advantages of layer-2 AES hardware which can operate in a test or loopback mode.

Information security is a critical requirement in healthcare systems. Medical electronic devices are mandated to use strong encryption to protect data. The U.S. Health Information Technology for Economic and Clinical Health (HITECH) Act addresses, among other things, the privacy and security concerns associated with the electronic transmission of health information, and the associated penalties for breaches of the information. Arising from this, the U.S. Department of Health and Human Services (HHS) recommended that medical devices be certified for the Federal Information Process Standard (FIPS) 140-2 encryption standard.

Figure 1: Wi-Fi Module Functional Architecture

Figure 1: Wi-Fi Module Functional Architecture

Within medical devices, encryption is carried out by cryptographic subsystems or modules, either in hardware or software. The FIPS 140-2 standard lays out the requirements and standards to protect the modules themselves—to protect the protector. It covers areas related to the secure design and implementation of a cryptographic module—including module specification, interfaces, authentication, key management, self-tests and mitigation of attacks.

The Cryptographic Module Validation Program (CMVP), a joint effort of the U.S. National Institute of Standards and Technology (NIST) and the Communications Security Establishment Canada (CSEC), validates cryptographic modules to the FIPS 140-2 standard. The standard was originally applied in systems employed by Federal Agencies, including the Department of Defense, to protect sensitive data, but has since been adopted into healthcare, apart from financial services, education and manufacturing.

Wi-Fi Use Grows

Medical devices and systems are increasingly using Wi-Fi as the primary means of connectivity. Wi-Fi uses the Advanced Encryption Standard (AES) for encrypting data before transmission—and this standard meets FIPS 140-2 requirements on strength of encryption.

However, CMVP involves several tests and must meet many other requirements before certification can be granted. As a prerequisite, a device needs to go through the Cryptographic Algorithm Validation Program (CAVP) that provides validation testing of FIPS-approved and NIST-recommended cryptographic algorithms and their individual components. Accredited Cryptographic and Security Testing (CST) laboratories conduct the tests.

CAVP validates the implementation of the algorithms—whether they adhere to the specifications of the cryptographic algorithm reference—by running tests that exercise the procedures and mathematical steps involved in the algorithms. For each algorithm, the CST laboratory generates input vectors that are then provided to the crypto module under test. The module in turn retrieves the resulting answers from the cryptographic algorithm implementation, which the laboratory test system verifies for accuracy—the Known Answer Test (KAT). We can see that the process involves obtaining the control of each algorithm implementation in isolation so that input test vectors and results can be collated.

Certification Problems

One of the difficulties from a Wi-Fi point of view has been these cryptographic loop-back tests. FIPS 140-2 approves only one of the methods of encryption and decryption in Wi-Fi— the Advanced Encryption Standard (AES) used in WPA2. Wi-Fi devices typically implement the AES process in hardware so as to ensure security processing at the required latency for all data rates and packet sizes. Unlike other crypto elements found in networking devices that address security of information payload at the application or network protocol layers, AES in Wi-Fi is a part of layer-2 functionality.

Figure 1 shows the functional architecture of a typical fully embedded Wi-Fi module. The AES crypto hardware resides in the datapath—packets are taken through it before transmission in the transmit path, and before forwarding to the network layer in the receive path. The Medium Access Controller (MAC processor) in the device normally only controls the crypto process—the resultant encrypted packets in the transmitter, for example, are directly provided to the layer-1 PHY hardware.

The crypto hardware is therefore not normally equipped with the required querying and loopback mechanisms required during CAVP/CMVP testing, and so certification would not be possible. A common way of addressing this requirement is to bypass the encryption hardware and carry out security processing in software. System developers then use a Wi-Fi module along with FIPS compliant software—the Wi-Fi Supplicant—to ensure certification. Carrying out encryption in software would mean being unable to support high data rates—the limitation being dependent on the processor’s capability. And in all cases, using software for the purpose would result in devices with higher power consumption and shorter battery life.

Fully Embedded FIPS-140-2 Functionality

Redpine’s RS9113 WiSeConnect module, FIPS-140-2 certified and listed by CMVP, provides fully embedded FIPS 140-2 functionality. As a result, a device’s layer-2 AES hardware can operate in a test or loopback mode—one where resultant encrypted or decrypted data is routed to the packet buffers that are accessible to the host processor interfaced to the module through USB, SDIO, UART or other standard interfaces.

Apart from AES with 128-bit key and 256-bit key used in Wi-Fi, the WiSeConnect module also contains other crypto functions that include SHA-1, SHA-256, SP800-90A, among others. In addition, the module contains an embedded TCP/IP stack with SSL, with the result being an ideal platform for the easy addition of FIPS 140-2 certified Wi-Fi functionality to medical devices.

In addition to validating the encryption mechanism, FIPS 140-2 also checks that modules are able to carry out periodic power-up self-tests to monitor for proper functioning of the security subsystems, and tests to verify the integrity of software being executed by the module’s internal processors. All this involves some complexity and overhead in the design of the system. A preferred way of building compliant medical devices with Wi-Fi connectivity is to use a certified, fully embedded module for the purpose.

Narasimhan Venkatesh is Senior Vice President of Advanced Technologies at Redpine Signals, and has 30 years of engineering and management experience wireless system design, semiconductor design, telecommunications, optical networking and avionics. He is a wireless specialist with responsibilities that include leading the development of wireless systems at Redpine’s India center, and their application into diverse industry areas. His current focus is on wireless connectivity in the Internet of Things.
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NVenkatesh-photo_webVenkatesh is a Fellow of the Indian National Academy of Engineering and holds a Masters Degree in Electrical Engineering from the Indian Institute of Technology, Madras, India.

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