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A PCS batch opening proof needs to Fiat-Shamir the evaluation claims #173

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chancharles92 opened this issue Feb 19, 2025 · 0 comments · Fixed by #174

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chancharles92 commented Feb 19, 2025 •

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In Hyperplonk, after running the sumchecks, the prover needs to generate a batch opening proof for the polynomial evaluations. In the current implementation:
https://github.com/EspressoSystems/hyperplonk/blob/main/hyperplonk/src/snark.rs#L610
https://github.com/EspressoSystems/hyperplonk/blob/main/subroutines/src/pcs/multilinear_kzg/batching.rs#L209
the Fiat-Shamir transcript (for generating the random challenge t) doesn't include the evaluation claims (i.e., the evaluation points and the evaluation values). This would be insecure, as an attacker can adaptively choose the evaluation values after knowing the challenge t.

Action items:

Fiat-shamir the evaluation values of the evaluation claims before batching.
Fiat-shamir the random evaluation point as well. (I didn't see an immediate attack without doing this, but I think it's safer to do so.)

cc @alxiong @mrain @zhenfeizhang

alxiong mentioned this issue

fix: append eval and eval_point to transcript #174

Merged

chancharles92 closed this as completed in #174

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