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An Efficient State Recovery Attack on the X-FCSR Family of Stream Ciphers

Publiceringsår: 2014
Språk: Engelska
Sidor: 1-22
Publikation/Tidskrift/Serie: Journal of Cryptology
Volym: 27
Nummer: 1
Dokumenttyp: Artikel
Förlag: Springer


We describe a state recovery attack on the X-FCSR family of stream ciphers. In this attack we analyse each block of output keystream and try to solve for the state. The solver will succeed when a number of state conditions are satisfied.
For X-FCSR-256, our best attack has a computational complexity of only 2^{4.7} table lookups per block of keystream, with an expected 2^{44.3} such blocks before the attack is successful. The precomputational storage requirement is 2^{33}.
For X-FCSR-128, the computational complexity of our best attack is 2^{16.3} table lookups per block of keystream, where we expect 2^{55.2} output blocks before the attack comes through. The precomputational storage requirement for X-FCSR-128 is 2^{67}.



  • Technology and Engineering
  • stream cipher
  • FCSR
  • X-FCSR
  • cryptanalysis
  • state recovery


  • ISSN: 0933-2790 (Print)
  • ISSN: 1432-1378 (Online)

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