About the FRI Protocol
The FRI (Fast, Reed-Solomon Interactive Oracle Proof of Proximity) protocol is the final component of RISC Zero's argument of computational integrity.
RISC Zero's STARK converts an assertion of computational integrity to an assertion about polynomial division. In the language of Reed-Solomon codes, this assertion about polynomial division can be re-framed as an assertion about block proximity. The FRI protocol finishes the argument by proving the assertion about block proximity.
Basic Function
Given a Merkle root, the FRI protocol is a recursive technique for proving that the associated Merkle leaves are associated with a low-degree polynomial.