Concurrent error detection and correction is an effective way to mitigate fault attacks in cryptographic hardware. Recent work on differential power analysis shows that even mathematically-secure cryptographic protocols may be vulnerable at the physical implementation level. By measuring energy consumed by a working digital circuit, it is possible to gain valuable information about the encryption algorithms used and even the specific encryption keys. Thwarting such attacks requires a new approach to logic and physical designs. This paper presents a systematic approach to fault tolerant cryptographic hardware designs. Firstly, the effectiveness of the Hamming code based error correction schemes as a fault tolerance method in stream ciphers is investigated. Coding is applied to Linear Feedback Shift Registers (LFSR) based stream cipher implementations. The method was implemented on industrial standard stream ciphers, e.g. A5/1(GSM), E0 (Bluetooth), RC4 (WEP), and W7. The performance variation of stream cipher algorithms with error detection and correction was studied by synthesising the designs on Field Programmable Logic Arrays (FPGA) and Application Specific Integrated Circuits (ASIC). Further, we analyse hardware building blocks to minimise switching activity of a circuit over all possible inputs and input transitions by adding redundant gates and increasing the overall number of signal transitions. We also discuss the overhead and compositional properties of uniformly-switching circuits.

Data driven architectures have significant potential in the design of high performance ASICs. By exploiting the inherent parallelism in the application, these architectures can maximize pipelining. The key consideration involved with the design of a data driven ASIC is ensuring that throughput is maximized while a relatively low area is maintained. Optimal throughput can be realized by ensuring that all operands arrive simultaneously at their corresponding operator node. If this condition is achieved, the underlying data flow graph is said to be balanced. If the initial data flow graph is unbalanced, buffers must be inserted to prevent the clogging of the pipeline along the shorter paths. A novel algorithm for the assignment of buffers in a data flow graph is proposed. The method can also be applied to achieve wave-pipelining in digital systems under certain restrictions. The algorithm uses a new application of the retiming technique; the number of buffers here is shown to be equal to the minimum number of buffers achieved by integer programming techniques. We also discuss an extension of this algorithm which can further reduce the number of buffers by altering the DFG without affecting functionality or performance. The time complexities of the proposed algorithms are O(V/spl times/E) and O(V/sup 2//spl times/logV), respectively, a considerable improvement over the existing strategies. Also proposed is a novel buffer distribution algorithm that exploits a unique feature of data driven operation. This procedure maximizes throughput by inserting substantially fewer buffers than other techniques. Experimental results show that the proposed algorithms outperform the existing methods.

We show that existing synthesis techniques may produce asynchronous circuits that are not initializable by gate level analysis tools even when the design is functionally initializable. Due to the absence of any initialization sequence, a fault simulator or test generator that assumes an unknown starting state will be completely ineffective for these circuits. In this paper, we show that proper consideration of initializability during the asynchronous circuit synthesis procedure can guarantee initializable implementations. We show that the assignment of don't cares during the synthesis procedure affects the initializability of the final implementation. We present a novel implicit enumeration procedure that selectively assigns don't cares to obtain an initializable implementation. Initialization sequences are obtained as a by-product of our synthesis procedure.

We present a procedure for synthesizing initializable asynchronous circuits from functionally uninitializable Signal Transition Graphs (STG). After characterizing the necessary conditions for functional uninitializability, we propose a technique that transforms the original STG into an equivalent, functionally initializable STG. It is shown that initializability can be achieved by sacrificing minimal concurrency without violating the syntactic properties of the STG required for a hazard-free implementation. The synthesis of a trigger module illustrates this procedure.>

Data driven architectures have the potential to exhibit higher performance and throughput when compared to their control driven counterparts. In order to ensure that these performance gains are realized, it is required that the underlying data flow graph (DFG) have no accumulation of data at its nodes. Hence, all operands should arrive simultaneously at a multi-input operation node. Buffers are therefore inserted to ensure these conditions. An algorithm for buffer distribution in a balanced DFG of order (V /spl times/ E) is proposed. The number of buffers in the proposed buffer distribution strategy is equal to the minimum number of buffers achieved by integer programming techniques. An extension of this algorithm, of order (V/sup 2/ /spl times/ log V) is proposed which can further reduce the number of buffers by altering the DFG while keeping the functionality and performance of the DFG intact. Performance results showing the improvement of these algorithms over the existing ones have been shown.