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Timing Attack against Protected RSA-CRT Implementation Used in PolarSSL

Abstract : In this paper, we present a timing attack against the RSA-CRT algorithm used in the current version 1.1.4 of PolarSSL, an open-source cryptographic library for embedded systems. This implementation uses a classical countermeasure to avoid two previous attacks of Schindler and another one due to Boneh and Brumley. However, a careful analysis reveals a bias in the implementation of Montgomery multiplication. We theoretically analyse the distribution of output values for Montgomery multiplication when the output is greater than the Montgomery constant, R. In this case, we show that an extra bit is set in the top most significant word of the output and a time variance can be observed. Then we present some proofs with reasonable assumptions to explain this bias due to an extra bit. Moreover, we show it can be used to mount an attack that reveals the factorisation. We also study another countermeasure and show its resistance against attacked library.
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Contributor : Pierre-Alain Fouque Connect in order to contact the contributor
Submitted on : Friday, December 12, 2014 - 9:27:07 AM
Last modification on : Thursday, April 4, 2019 - 10:18:05 AM
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Cyril Arnaud, Pierre-Alain Fouque. Timing Attack against Protected RSA-CRT Implementation Used in PolarSSL. Topics in Cryptology - 2013, Mar 2013, San Francisco, United States. pp.16, ⟨10.1007/978-3-642-36095-4_2⟩. ⟨hal-01094300⟩



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