Invited ABSTRACTThe Simon and Speck families of block ciphers were designed specifically to offer security on constrained devices, where simplicity of design is crucial. However, the intended use cases are diverse and demand flexibility in implementation. Simplicity, security, and flexibility are ever-present yet conflicting goals in cryptographic design. This paper outlines how these goals were balanced in the design of Simon and Speck.

Abstract. The last several years have witnessed a surge of activity in lightweight cryptographic design. Many lightweight block ciphers have been proposed, targeted mostly at hardware applications. Typically software performance has not been a priority, and consequently software performance for many of these algorithms is unexceptional. Simon and Speck are lightweight block cipher families developed by the U.S. National Security Agency for high performance in constrained hardware and software environments. In this paper, we discuss software performance and demonstrate how to achieve high performance implementations of Simon and Speck on the AVR family of 8-bit microcontrollers. Both ciphers compare favorably to other lightweight block ciphers on this platform. Indeed, Speck seems to have better overall performance than any existing block cipher -lightweight or not.

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