A key recovery attack on MDPC with CCA security using decoding errors

Research output: Chapter in Book/Report/Conference proceedingPaper in conference proceedingpeer-review

Abstract

Algorithms for secure encryption in a post-quantum world are currently receiving a lot of attention in the research community, including several larger projects and a standardization effort from NIST. One of the most promising algorithms is the code-based scheme called QC-MDPC, which has excellent performance and a small public key size. In this work we present a very efficient key recovery attack on the QCMDPC scheme using the fact that decryption uses an iterative decoding step and this can fail with some small probability. We identify a dependence between the secret key and the failure in decoding. This can be used to build what we refer to as a distance spectrum for the secret key, which is the set of all distances between any two ones in the secret key. In a reconstruction step we then determine the secret key from the distance spectrum. The attack has been implemented and tested on a proposed instance of QC-MDPC for 80 bit security. It successfully recovers the secret key in minutes. A slightly modified version of the attack can be applied on proposed versions of the QC-MDPC scheme that provides IND-CCA security. The attack is a bit more complex in this case, but still very much below the security level. The reason why we can break schemes with proved CCA security is that the model for these proofs typically does not include the decoding error possibility.

Original languageEnglish
Title of host publicationAdvances in Cryptology - ASIACRYPT 2016 - 22nd International Conference on the Theory and Application of Cryptology and Information Security, Proceedings
PublisherSpringer
Pages789-815
Number of pages27
Volume10031 LNCS
ISBN (Print)9783662538869
DOIs
Publication statusPublished - 2016
Event22nd Annual International Conference on the Theory and Applications of Cryptology and Information Security (ASIACRYPT), 2016 - Hanoi, Viet Nam
Duration: 2016 Dec 42016 Dec 8

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume10031 LNCS
ISSN (Print)03029743
ISSN (Electronic)16113349

Conference

Conference22nd Annual International Conference on the Theory and Applications of Cryptology and Information Security (ASIACRYPT), 2016
Country/TerritoryViet Nam
CityHanoi
Period2016/12/042016/12/08

Subject classification (UKÄ)

  • Computer Science

Free keywords

  • CCA-security
  • Key-recovery attack
  • Post-quantum cryptography
  • QC-MDPC
  • Reaction attack

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