IACR News item: 20 December 2011
PhD Database
Name: Arshad Ali
Topic: New Attacks on FCSR-based Stream Ciphers
Category: secret-key cryptography
Description: This thesis presents a new family of cryptanalytic attacks on a class of binary\r\nadditive synchronous stream ciphers, the theory of which is based on the properties\r\nof 2-adic numbers. We refer to this new family of cryptanalytic attacks as State Transition Attacks (STAs); we identify three variants of this class of attack, namely Conventional State Transition Attacks (CSTAs), Fast State\r\nTransition Attacks (FSTAs) and Improved State Transition Attacks (ISTAs). These attack variants give rise to trade-offs between data, time and memory complexities. The thesis describes STAs on a class of binary additive synchronous stream ciphers whose keystream generators use l-sequences, which are generated by binary Feedback with Carry Shift Registers (FCSRs). A new theory of linearisation intervals for FCSR state update functions is also presented, and results on correlations between the feedback bit and the Hamming weights of the main and carry registers of Galois FCSRs are developed. These\r\ntheoretical findings are used to cryptanalyse an eSTREAM candidate known as F-FCSR-H v2, as well as two variants of this cipher, known as F-FCSR-H and F-FCSR-16. This cryptanalysis yields State Recovery Algorithms (SRAs)\r\nfor these ciphers. The cryptanalytic attacks on F-FCSR-H v2, F-FCSR-H and F-FCSR-16 presented in this thesis are the most efficient attacks known so far on these ciphers. The thesis also presents a FCSR key recovery algorithm which works in conjunction with the SRAs in order to recover the e ective key used in these ciphers.\r\n
\r\n The thesis also presents various techniques, which can be considered as pre-requisite for simulating new attacks on FCSR-based stream ciphers. In order to describe these techniques, the thesis defines a small-scale variant of the F-FCSR-H type keystream generators and names it as T-cipher. The thesis develops a statistical analysis for the T-cipher and uses it to describe various aspects of the sequences generated by such ciph[...]
Topic: New Attacks on FCSR-based Stream Ciphers
Category: secret-key cryptography
Description: This thesis presents a new family of cryptanalytic attacks on a class of binary\r\nadditive synchronous stream ciphers, the theory of which is based on the properties\r\nof 2-adic numbers. We refer to this new family of cryptanalytic attacks as State Transition Attacks (STAs); we identify three variants of this class of attack, namely Conventional State Transition Attacks (CSTAs), Fast State\r\nTransition Attacks (FSTAs) and Improved State Transition Attacks (ISTAs). These attack variants give rise to trade-offs between data, time and memory complexities. The thesis describes STAs on a class of binary additive synchronous stream ciphers whose keystream generators use l-sequences, which are generated by binary Feedback with Carry Shift Registers (FCSRs). A new theory of linearisation intervals for FCSR state update functions is also presented, and results on correlations between the feedback bit and the Hamming weights of the main and carry registers of Galois FCSRs are developed. These\r\ntheoretical findings are used to cryptanalyse an eSTREAM candidate known as F-FCSR-H v2, as well as two variants of this cipher, known as F-FCSR-H and F-FCSR-16. This cryptanalysis yields State Recovery Algorithms (SRAs)\r\nfor these ciphers. The cryptanalytic attacks on F-FCSR-H v2, F-FCSR-H and F-FCSR-16 presented in this thesis are the most efficient attacks known so far on these ciphers. The thesis also presents a FCSR key recovery algorithm which works in conjunction with the SRAs in order to recover the e ective key used in these ciphers.\r\n
\r\n The thesis also presents various techniques, which can be considered as pre-requisite for simulating new attacks on FCSR-based stream ciphers. In order to describe these techniques, the thesis defines a small-scale variant of the F-FCSR-H type keystream generators and names it as T-cipher. The thesis develops a statistical analysis for the T-cipher and uses it to describe various aspects of the sequences generated by such ciph[...]
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