In cryptology we commonly face the problem of finding an unknown key  K  from the output of an easily computable keyed function  F  ( C  , K  ) where the attacker has the power to choose the public variable  C  . In this work we focus on self-synchronizing stream ciphers. First we show how to model these primitives in the above-mentioned general problem by relating appropriate functions  F  to the underlying ciphers. Then we apply the recently proposed framework presented at AfricaCrypt'08 by Fischer  et. al.  for dealing with this kind of problems to the proposed T-function based self-synchronizing stream cipher by Klimov and Shamir at FSE'05 and show how to deduce some non-trivial information about the key. We also open a new window for answering a crucial question raised by Fischer  et. al.  regarding the problem of finding weak IV bits which is essential for their attack.
['Shahram Khazaei', 'Willi Meier']
New Directions in Cryptanalysis of Self-Synchronizing Stream Ciphers