@inproceedings{e4ccbfe4d5ec4e0dac230ed0934226c5,

title = "A reaction attack on the QC-LDPC mceliece cryptosystem",

abstract = "Guo et al. recently presented a reaction attack against the QC-MDPC McEliece cryptosystem. Their attack is based on the observation that when a bit-flipping decoding algorithm is used in the QC-MDPC McEliece, then there exists a dependence between the secret matrix H and the failure probability of the bit-flipping algorithm. This dependence can be exploited to reveal the matrix H which constitutes the private key in the cryptosystem. It was conjectured that such dependence is present even when a soft-decision decoding algorithm is used instead of a bit-flipping algorithm. This paper shows that a similar dependence between the secret matrix H and the failure probability of a decoding algorithm is also present in the QC-LDPC McEliece cryptosystem. Unlike QC-MDPC McEliece, the secret key in QC-LDPC McEliece also contains matrices S and Q in addition to the matrix H. We observe that there also exists a dependence between the failure probability and the matrix Q. We show that these dependences leak enough information to allow an attacker to construct a sparse parity-check matrix for the public code. This parity-check matrix can then be used for decrypting ciphertexts. We tested the attack on an implementation of the QC-LDPC McEliece using a soft-decision decoding algorithm. Thus we also confirmed that soft-decision decoding algorithms can be vulnerable to leaking information about the secret key.",

keywords = "QC-LDPC McEliece cryptosystem, Reaction attack, Soft-decision decoding",

author = "Tom{\'a}{\v s} Fab{\v s}i{\v c} and Viliam Hromada and Paul Stankovski and Pavol Zajac and Qian Guo and Thomas Johansson",

year = "2017",

doi = "10.1007/978-3-319-59879-6_4",

language = "English",

isbn = "9783319598789",

volume = "10346 LNCS",

series = "Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)",

publisher = "Springer",

pages = "51--68",

booktitle = "Post-Quantum Cryptography - 8th International Workshop, PQCrypto 2017, Proceedings",

address = "Germany",

note = "8th International Workshop on Post-Quantum Cryptography, PQCrypto 2017 ; Conference date: 26-06-2017 Through 28-06-2017",

}