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Two attacks on rank metric code-based schemes: RankSign and an IBE scheme

Abstract : RankSign [29] is a code-based signature scheme proposed to the NIST competition for quantum-safe cryptography [5] and, moreover , is a fundamental building block of a new Identity-Based-Encryption (IBE) [25]. This signature scheme is based on the rank metric and enjoys remarkably small key sizes, about 10KBytes for an intended level of security of 128 bits. Unfortunately we will show that all the parameters proposed for this scheme in [5] can be broken by an algebraic attack that exploits the fact that the augmented LRPC codes used in this scheme have very low weight codewords. Therefore, without RankSign the IBE cannot be instantiated at this time. As a second contribution we will show that the problem is deeper than finding a new signature in rank-based cryptography, we also found an attack on the generic problem upon which its security reduction relies. However, contrarily to the RankSign scheme, it seems that the parameters of the IBE scheme could be chosen in order to avoid our attack. Finally, we have also shown that if one replaces the rank metric in the [25] IBE scheme by the Hamming metric, then a devastating attack can be found.
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https://hal.inria.fr/hal-01957207
Contributor : Jean-Pierre Tillich <>
Submitted on : Monday, December 17, 2018 - 10:56:40 AM
Last modification on : Monday, March 4, 2019 - 11:07:40 AM
Long-term archiving on: : Monday, March 18, 2019 - 1:34:39 PM

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Thomas Debris-Alazard, Jean-Pierre Tillich. Two attacks on rank metric code-based schemes: RankSign and an IBE scheme. ASIACRYPT 2018 - 24th International Conference on the Theory and Application of Cryptology and Information Security, Dec 2018, Brisbane, Australia. pp.62-92, ⟨10.1007/978-3-030-03326-2_3⟩. ⟨hal-01957207⟩

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