Revisiting a recent resource-efficient technique for increasing the throughput of stream ciphers

At CT-RSA 2014, Armknecht and Mikhalev presented a new technique for increasing the throughput of stream ciphers that are based on Feedback Shift Registers (FSRs) which requires practically no additional memory. The authors provided concise sufficient conditions for the applicability of this technique and demonstrated its usefulness on the stream cipher Grain-128. However, as these conditions are quite involved, the authors raised as an open question if and to what extent this technique can be applied to other ciphers as well. In this work, we revisit this technique and examine its applicability to other stream ciphers. On the one hand we show on the example of Grain-128a that the technique can be successfully applied to other ciphers as well. On the other hand we list several stream ciphers where the technique is not applicable for different structural reasons.