On lightweight stream ciphers with shorter internal states. (English) Zbl 1382.94050

Leander, Gregor (ed.), Fast software encryption. 22nd international workshop, FSE 2015, Istanbul, Turkey, March 8–11, 2015. Revised selected papers. Berlin: Springer (ISBN 978-3-662-48115-8/pbk; 978-3-662-48116-5/ebook). Lecture Notes in Computer Science 9054, 451-470 (2015).
Summary: To be resistant against certain time-memory-data-tradeoff (TMDTO) attacks, a common rule of thumb says that the internal state size of a stream cipher should be at least twice the security parameter. As memory gates are usually the most area and power consuming components, this implies a sever limitation with respect to possible lightweight implementations.{
} In this work, we revisit this rule. We argue that a simple shift in the established design paradigm, namely to involve the fixed secret key not only in the initialization process but in the keystream generation phase as well, enables stream ciphers with smaller area size for two reasons. First, it improves the resistance against the mentioned TMDTO attacks which allows to choose smaller state sizes. Second, one can make use of the fact that storing a fixed value (here: the key) requires less area size than realizing a register of the same length. We demonstrate the feasibility of this approach by describing and implementing a concrete stream cipher Sprout which uses significantly less area than comparable existing lightweight stream ciphers.
For the entire collection see [Zbl 1318.68029].


94A60 Cryptography
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