Paper 2022/357

An Effective Lower Bound on the Number of Orientable Supersingular Elliptic Curves

Antonin Leroux

In this article, we prove a generic lower bound on the number of $\mathfrak{O}$-orientable supersingular curves over $\mathbb{F}_{p^2}$, i.e curves that admit an embedding of the quadratic order $\mathfrak{O}$ inside their endomorphism ring. Prior to this work, the only known effective lower-bound is restricted to small discriminants. Our main result targets the case of fundamental discriminants and we derive a generic bound using the expansion properties of the supersingular isogeny graphs. Our work is motivated by isogeny-based cryptography and the increasing number of protocols based on $\mathfrak{O}$-oriented curves. In particular, our lower bound provides a complexity estimate for the brute-force attack against the new $\mathfrak{O}$-uber isogeny problem introduced by De Feo, Delpech de Saint Guilhem, Fouotsa, Kutas, Leroux, Petit, Silva and Wesolowski in their recent article on the SETA encryption scheme.

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Public-key cryptography
Publication info
isogeny based cryptography quaternion orders quadratic orders
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antonin leroux @ polytechnique org
2022-06-09: last of 2 revisions
2022-03-18: received
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      author = {Antonin Leroux},
      title = {An Effective Lower Bound on the Number of Orientable Supersingular Elliptic Curves},
      howpublished = {Cryptology ePrint Archive, Paper 2022/357},
      year = {2022},
      note = {\url{}},
      url = {}
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