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On the Concrete Security of Non-interactive FRI

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Security and Cryptography for Networks (SCN 2024)

Abstract

FRI is a cryptographic protocol widely deployed today as a building block of many efficient SNARKs that help secure transactions of hundreds of millions of dollars per day. The Fiat-Shamir security of FRI—vital for understanding the security of FRI-based SNARKs—has only recently been formalized and established by Block et al. (ASIACRYPT ’23).

In this work, we complement the result of Block et al. by providing a thorough concrete security analysis of non-interactive FRI under various parameter settings from protocols deploying (or soon to be deploying) FRI today. We find that these parameters nearly achieve their desired security targets (being at most 1-bit less secure than their targets) for non-interactive FRI with respect to a certain security conjecture about the FRI Protocol. However, in all but one set of parameters, we find that the provable security of non-interactive FRI under these parameters is severely lacking, being anywhere between 21- and 63-bits less secure than the conjectured security. The conjectured security of FRI assumes that known attacks are optimal, the security of these systems would be severely compromised should a better attack be discovered. In light of this, we present parameter guidelines for achieving 100-bits of provable security for non-interactive FRI along with a methodology for tuning these parameters to suit the needs of protocol designers.

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Notes

  1. 1.

    An interactive protocol is public-coin if all messages sent by the verifier are sampled uniformly at random and are independent of all prior protocol messages.

  2. 2.

    See Remark 2 for a discussion on the difference between these notions.

  3. 3.

    A similar definition for bits of security is given in the ethSTARK documentation [26].

  4. 4.

    To the best of our knowledge, all projects using this conjecture set \(\delta = 1-\rho \).

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Acknowledgements

The authors would like to thank Matthew Green for all the helpful presentation suggestions of this work. Alexander R. Block was supported by DARPA under Contract Nos. HR00112020022 and HR00112020025. Pratyush Ranjan Tiwari was supported by the Ethereum Foundation’s grant FY23-1087, and partly supported by a Security & Privacy research gift from Google, a research gift from Cisco. The views, opinions, findings, conclusions, and/or recommendations expressed in this material are those of the authors and should not be interpreted as reflecting the position or policy of DARPA or the United States Government, and no official endorsement should be inferred.

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Block, A.R., Tiwari, P.R. (2024). On the Concrete Security of Non-interactive FRI. In: Galdi, C., Phan, D.H. (eds) Security and Cryptography for Networks. SCN 2024. Lecture Notes in Computer Science, vol 14973. Springer, Cham. https://doi.org/10.1007/978-3-031-71070-4_13

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