International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: X-FCSR: a new software oriented stream cipher based upon FCSRs

Francois Arnault
Thierry P. Berger
Cédric Lauradoux
Marine Minier
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Abstract: Feedback with Carry Shift Registers (FCSRs) are a promising alternative to LFSRs in the design of stream cipher. The previous constructions based on FCSRs were dedicated to hardware applications. In this paper, we will describe X-FCSR a family of software oriented stream cipher using FCSRs. The core of the system is composed of two 256-bits FCSRs. We propose two versions: X-FCSR-128 and X-FCSR-256 which output respectively 128 and 256 bits at each iteration. We study the resistance of our design against several cryptanalyses. In this way, we achieve a high throughput and secure stream ciphers suitable for software applications (6.3 cycles/byte).
  title={X-FCSR: a new software oriented stream cipher based upon FCSRs},
  booktitle={IACR Eprint archive},
  keywords={secret-key cryptography / stream cipher, FCSRs, software design, cryptanalysis},
  note={this paper was accepted as a short paper at Indocrypt 2007 13782 received 25 Sep 2007, last revised 26 Sep 2007},
  author={Francois Arnault and Thierry P. Berger and Cédric Lauradoux and Marine Minier},