Fast Correlation Attack on Stream Cipher.

Date of Submission

December 2007

Date of Award

Winter 12-12-2008

Institute Name (Publisher)

Indian Statistical Institute

Document Type

Master's Dissertation

Degree Name

Master of Technology

Subject Name

Computer Science


Cryptology and Security Research Unit (CSRU-Kolkata)


Palit, Sarbani (CVPR-Kolkata; ISI)

Abstract (Summary of the Work)

Stream ciphers form an important class of ciphersystems. Their speed over that of block ciphers and less complex hardware circuitry make it advantageous to use stream ciphers in many applications.In a binary additive stream cipher, the ciphertext is produced by bitwise addition of the plaintext with the key stream, all in binary. The key stream generator is initialized using a secret key. a popular key-stream generator used in stream ciphers consists of several LFSRs combined through a nonlinear boolen function.Attacks that exploit the similarity between the ciphertext and the LFSR outputs, are termed correlation attack. The nature of the cipher system allows each LFSR to be analysed seperately, thus leading to a divide and conquer strategy. The idea of fast correlation attack, which eliminates the need for an exhaustive search of the LFSR initial conditions was first proposed by Meier and Staffelbach [1]. A number of fast correlation attacks were later proposed. However, fast correlation attacks suffer from one or more of the following drawbacks.1. The presence of a preprocessing phase of considerable complexity which naturally increases the overall decoding time.2. An iterative phase which takes time to converge.3. The assumption of a combining functiion that is not correlation immune and also known to the decrypter.The algorithm proposed here is free of all these restrictions which is in the sideline of Palit, Roy and Arindom [2].


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Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


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