PQCrypto 2019

PQCrypto 2019 was held at Ronghui Spa Hotel in Chongqing, China on May 8-10, 2019. Prior to the conference, two other PQC events (the PQC 2019 summer school on May 6th and the 4th Asia PQC Forum on May 7th) were held at the same place.

The session on isogeny-based cryptography was held in the afternoon of May 9. It included three talks by young researchers:

  • Thomas Decru “Faster SeaSign signatures through improved rejection sampling” (joint work with Lorenz Panny and Frederik Vercauteren)

    This talk presented a faster variant of the SeaSign signature scheme by improving rejection sampling, which is a key technical ingredient of SeaSign. To obtain a practical isogeny-based (post-quantum) signature scheme is an important research direction in this field. This work advances a nice step towards the goal, however, it does not yet succeed.

  • Yan Bo Ti “Genus Two Isogeny Cryptography” (joint work with Victor Flynn)

    First, this talk presented a systematic method for finding collisions of the Charles-Goren-Lauter type genus-two hash function (which was suggested in a previous paper of mine). The collision finding was accomplished based on a closer look of the structure of isogeny graphs in genus two. A little surprisingly, it is now fixed by a very recent paper by Castryck, Decru, and Smith (eprint arxiv 2019/296), which reformulates it by using genus-two “superspecial” subgraphs. The talk also proposed a SIDH-type key exchange in genus two, in which (2,2)- and (3,3)-isogenies are used instead of 2- and 3-isogenies in the genus one case, respectively.

  • Michael Meyer “On Lions and Elligators: An efficient constant-time implementation of CSIDH” (joint work with Fabio Campos and Steffen Reith)

    This presentation proposed an efficient constant-time implementation of CSIDH. In the authors’ previous paper (INDOCRYPT 2018), they initiated an improvement of CSIDH implementation, which resulted in a faster algorithm than the original. However, this previous one leaks various information about the private key. Therefore, for obtaining side-channel leakage resistance, this talk modified how to sample key elements and used dummy isogenies, and then obtained a constant-time implementation (with several efficiency improvements furthermore).

Moreover, there were two invited talks which are relevant to this blog. One was by Tsuyoshi Takagi (Univ. of Tokyo), and the title was “Computational Challenge Problems in Post-Quantum Cryptography”, in which he first briefly reviewed the NIST PQC standardization, and then introduced PQC challenge problems with focus on the Fukuoka MQ Challenge and the Darmstadt Lattice Challenge. The other was given by Dustin Moody (NIST) on “Round 2 of NIST PQC Competition”. He carefully summarized the history of the competition and, for all the round 2 submissions, he made brief comments on advantages and/or unique features of the schemes. He also very briefly mentioned the future schedule of the competition.

— Katsuyuki Takashima

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