Soundness issue with Plonky2 look up tables

Vulnerability Description

Plonky2 is a SNARK implementation based on techniques from PLONK and FRI. Lookup tables, whose length is not divisible by 26 = floor(num_routed_wires / 3) always include the 0 -> 0 input-output pair. Thus a malicious prover can always prove that f(0) = 0 for any lookup table f (unless its length happens to be divisible by 26). The cause of problem is that the LookupTableGate-s are padded with zeros. A workaround from the user side is to extend the table (by repeating some entries) so that its length becomes divisible by 26. This vulnerability is fixed in 1.0.1.

References

• https://github.com/0xPolygonZero/plonky2/security/advisories/GHSA-hj49-h7fq-px5h
• https://github.com/0xPolygonZero/plonky2/commit/091047f7f10cae082716f3738ad59a583835f7b6
• https://github.com/0xPolygonZero/plonky2/blob/main/plonky2/src/plonk/prover.rs#L97