On physical obfuscation of cryptographic algorithms

Abstract

We describe a solution for physically obfuscating the representation of a cipher, to augment chips resistance against physical threats, by combining ideas from masking techniques and Physical Obfuscated Keys (POKs). With embedded chips - like RFID tags - as main motivation, we apply this strategy to the representation of a Linear Feedback Shift Register (LFSR). The application of this technique to LFSR-based stream ciphers, such as the Self Shrinking Generator, enables to share key materials between several chips within a system while increasing the resistance of the system against compromise of chips. An extension of our ideas to non-linear ciphers is also presented with an illustration onto Trivium. © 2009 Springer-Verlag.