Common Reference String

The collection of all public parameters required to run a protocol - usually in the context of SNARKs and polynomial commitment schemes.

In polynomial commitment schemes and SNARKs - like may other cryptographic protocols - different parties need to agree on some common parameters. These often include what kind of mathematical objects they will be manipulating (integers, points on an elliptic curve, lattices, etc…), a prime number, a generator of a cyclic group. Once a setup has been run to determine all the necessary parameters, they are collected into a string and are published for future reference. This collection (string) is what we call a common reference string.

Trusted Setups. In some cases the common parameters are constructed using information that needs to remain secret for the protocol to be secure. In this case we refer to the setup as a Trusted Setup and the string of parameters as a Structured Reference String.