Lightweight crypto for lightweight unmanned arial systems
Kevin R. Driscoll · 2018
There are three different possible applications of cryptography on an Unmanned Aerial System (UAS). These include remote control, streaming payload data, and on-board memory. On a lightweight UAS, all three of these can have severe size weight and power (SWaP) constraints. To minimize SWaP, encryption should be implemented in software that can fit into a processor that already exists on-board the UAS. Again, to minimize SWaP, this processor would be shared with other applications. To minimize its intrusion into such a multi-application environment, the encryption algorithm should minimize its use of program memory, data memory, and processor cycles. Minimizing processor cycles, particularly memory accesses, also minimizes power consumption. The algorithm also should work well with frequent context switching in a heavily multi-tasked environment. In addition to these requirements that all three share, each of the three can have unique requirements. Pilot-in-the-loop remote control would require integrity, and the integrity would be more important than secrecy. Pilot-in-the-loop remote control also would require very low latency. Remotely piloting the UAS would require a communication loop that included gathering on-board sensor information, encrypting this sensor information, transmitting it to the ground, decrypting the transmission, encrypting the response from the ground pilot, transmitting the encrypted response to the UAS, and decrypting the response. This means that each command loop would require four passes through the encryption algorithm. If a block cipher were used, there would be additional delays. Given all the other delays in this piloting command loop, these added encryption delays could be problematic. Streaming payload data (e.g., video) can require very high bandwidth. Encrypting this data would require a very high speed algorithm, but not necessarily low latency or high integrity. If the UAS contains software and/or data that the owner would want to keep secret and if the UAS could be lost such that an adversary could retrieve it before the owner could protect it, the software and/or data should be encrypted so that a fast "zeroize" of the key could protect that software and/or data. Encrypting software and/or the data it uses would require a fast, low latency, very small footprint algorithm. None of the well-known existing encryption algorithms, including those purporting to be lightweight, are a good match to these requirements. A family algorithms has been developed specifically for these types of requirements. Compared to the standard AES-GCM encryption, these algorithms are less than 1/10 the memory size and almost 100 times the speed. This paper will describe the requirements in more detail and how these new algorithms are better than any existing algorithm to meet these requirements.