Abstract
In 1989, Tsujii, Fujioka, and Hirayama proposed a family of multivariate public key cryptosystems, where the public key is given as a set of multivariate rational functions of degree 4. These cryptosystems are constructed via composition of two quadratic rational maps. In this paper, we present the cryptanalysis of this family of cryptosystems. The key point of our attack is to transform a problem of decomposition of two rational maps into a problem of decomposition of two polynomial maps. We develop a new improved 2R decomposition method and other new techniques, which allows us to find an equivalent decomposition of the rational maps to break the system completely. For the example suggested for practical applications, it is very fast to derive an equivalent private key, and it requires only a few seconds on a standard PC.
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Ding, J., Wagner, J. (2008). Cryptanalysis of Rational Multivariate Public Key Cryptosystems. In: Buchmann, J., Ding, J. (eds) Post-Quantum Cryptography. PQCrypto 2008. Lecture Notes in Computer Science, vol 5299. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-88403-3_9
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DOI: https://doi.org/10.1007/978-3-540-88403-3_9
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-540-88402-6
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