Abstract
The Fibonacci-to-Galois transformation is useful for reducing the propagation delay of feedback shift register-based stream ciphers and hash functions. In this paper, we extend it to handle Galois-to-Galois case as well as feedforward connections. This makes possible transforming Trivium stream cipher and increasing its keystream data rate by 27 % without any penalty in area. The presented transformation might open new possibilities for cryptanalysis of Trivium, since it induces a class of stream ciphers which generate the same set of keystreams as Trivium, but have a different structure.
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Notes
- 1.
An \(n\)-bit NLFSR is uniform if, for all \(i \in \{\tau ,\tau +1,\ldots ,n-1\}\), the largest index of variables of function \(g_i\) in (2) is smaller than or equal to \(\tau \), where \(\tau \) is the maximal index such that, for all \(j \in \{0,1,\ldots ,\tau -1\}\), \(g_j = 0\).
- 2.
We use an \(n\)-bit ring as a simplification of an \(n\)-bit shift register which shows the structure of its feedback/feedforward connections. The gates implementing GF(2) addition (XORs) are omitted and the gates implementing GF(2) multiplication (ANDs) are represented by a dot. Everything unnecessary for structural analysis is removed.
- 3.
Note that in this case the initial states are the same but generally they can be different [22].
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Acknowledgements
This work was supported in part the research grant No 621-2010-4388 from the Swedish Research Council and in part by the research grant No SM12-0005 from the Swedish Foundation for Strategic Research.
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Dubrova, E. (2014). An Equivalence-Preserving Transformation of Shift Registers. In: Schmidt, KU., Winterhof, A. (eds) Sequences and Their Applications - SETA 2014. SETA 2014. Lecture Notes in Computer Science(), vol 8865. Springer, Cham. https://doi.org/10.1007/978-3-319-12325-7_16
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