Design Challenges for a Differential-Power-Analysis Aware GALS-based AES Crypto ASIC

In recent years several successful GALS realizations have been presented. The core of a GALS system is a locally synchronous island that is designed using industry standard synchronous design methodologies. In principle, any functional synchronous block can be encapsulated as a locally synchronous island to form a GALS module. There are, however, several important trade-offs and design decisions involved in doing so. Partitioning a design into several GALS compatible modules is still the most difficult task facing GALS system designers. The controlling state machine of a synchronous functional block may need to be enhanced significantly to accommodate varying latencies involved in data transfers between GALS modules.Such design challenges can not be easily generalized, and in this paper, are presented based on the experiences of designing a GALS system that implements a cryptographic algorithm. The example design uses the GALS methodology to improve resistance against cryptographic power attacks. The problem of side channel attacks against hardware implementations of cryptographic algorithms are briefly presented first, and the GALS architecture featuring several countermeasures against such attacks is introduced. The main part of the paper concentrates on the design decisions involved in the development of this architecture.