# CLOCK CONTROL SEQUENCE RECONSTRUCTION IN THE GENERALIZED SHRINKING GENERATOR

### Slobodan Petrović

#### Abstract

An algorithm is presented that reconstructs the clock control sequence in the generalized shrinking generator in the presence of noise. The shrinking generator is first reduced to a step 1/step E generator, where E depends on the maximum length of runs of zeros in the output sequence of its clocking part. Then a directed depth-first like search for optimal and suboptimal paths in the edit distance matrix corresponding to the generator is performed. The permitted path weight deviation from the optimum is determined by the noise level in the statistical model of the generator. Since the algorithm is deterministic, the correct clock control sequence is guaranteed to be found, unlike many known algorithms of this kind. Experimental results show that the algorithm converges to the correct solution relatively fast even if the noise level is high.

#### References

- Coppersmith, D., Krawczyk, H., and Mansour, Y. (1994). The shrinking generator. In Procceings of Crypto 93, Lecture Notes in Computer Science 773, pages 22-39. Springer-Verlag.
- Golic, J. and Mihaljevic, M. (1991). A generalized correlation attack on a class of stream ciphers based on the levenshtein distance. Journal of Cryptology, 3(3):201-212.

#### Paper Citation

#### in Harvard Style

Petrović S. (2007). **CLOCK CONTROL SEQUENCE RECONSTRUCTION IN THE GENERALIZED SHRINKING GENERATOR** . In *Proceedings of the Second International Conference on Security and Cryptography - Volume 1: SECRYPT, (ICETE 2007)* ISBN 978-989-8111-12-8, pages 259-262. DOI: 10.5220/0002118402590262

#### in Bibtex Style

@conference{secrypt07,

author={Slobodan Petrović},

title={CLOCK CONTROL SEQUENCE RECONSTRUCTION IN THE GENERALIZED SHRINKING GENERATOR},

booktitle={Proceedings of the Second International Conference on Security and Cryptography - Volume 1: SECRYPT, (ICETE 2007)},

year={2007},

pages={259-262},

publisher={SciTePress},

organization={INSTICC},

doi={10.5220/0002118402590262},

isbn={978-989-8111-12-8},

}

#### in EndNote Style

TY - CONF

JO - Proceedings of the Second International Conference on Security and Cryptography - Volume 1: SECRYPT, (ICETE 2007)

TI - CLOCK CONTROL SEQUENCE RECONSTRUCTION IN THE GENERALIZED SHRINKING GENERATOR

SN - 978-989-8111-12-8

AU - Petrović S.

PY - 2007

SP - 259

EP - 262

DO - 10.5220/0002118402590262