STIR: Reed-Solomon Proximity Testing with Fewer Queries

We present STIR (Shift To Improve Rate), an interactive oracle proof of proximity (IOPP) for Reed-Solomon codes that achieves the best known query complexity of any concretely efficient IOPP for this problem. For $\lambda$ bits of security, STIR has query complexity $O(\log d + \lambda \cdot \log \log d )$, while FRI, a popular protocol, has query complexity $O(\lambda \cdot \log d )$ (including variants of FRI based on conjectured security assumptions). STIR relies on a new technique for recursively improving the rate of the tested Reed-Solomon code.

We provide an implementation of STIR compiled to a SNARK. Compared to a highly-optimized implementation of FRI, STIR achieves an improvement in argument size that ranges from $1.25\times$ to $2.46\times$ depending on the chosen parameters, with similar prover and verifier running times. For example, in order to achieve 128 bits of security for degree $2^{26}$ and rate $1/4$, STIR has argument size $114$ KiB, compared to $211$ KiB for FRI.