7.2. Certificate Thumbprint Binding

The binding between the certificate and access token specified in Section 3.1 uses a cryptographic hash of the certificate. It relies on the hash function having sufficient second-preimage resistance so as to make it computationally infeasible to find or create another certificate that produces to the same hash output value. The SHA-256 hash function was used because it meets the aforementioned requirement while being widely available. If, in the future, certificate thumbprints need to be computed using hash function(s) other than SHA-256, it is suggested that, for additional related JWT confirmation methods, members be defined for that purpose and registered in the IANA "JWT Confirmation Methods" registry [IANA.JWT.Claims] for JWT cnf member values.

Community knowledge about the strength of various algorithms and feasible attacks can change suddenly, and experience shows that a document about security is a point-in-time statement. Readers are advised to seek out any errata or updates that apply to this document.