Hi all, Any idea whether we can use both of the above approaches as valid methods to calculate the "x5t#S256" parameter? Appreciate your input on this.
Best Regards, Thamindu Jayawickrama On Wed, Jan 10, 2024 at 9:40 AM Thamindu Dilshan Jayawickrama < thamindudill...@gmail.com> wrote: > Hi all, > > I have initiated this mail thread to get your opinion on the correct > approach of calculating the "x5t#S256" parameter in the JWKS response. JWS > specification [1 > <https://datatracker.ietf.org/doc/html/rfc7515#section-4.1.8>] defines > the "x5t#S256" parameter as follows. > > """ > The "x5t#S256" (X.509 certificate SHA-256 thumbprint) Header > Parameter is a base64url-encoded SHA-256 thumbprint (a.k.a. digest) > of the DER encoding of the X.509 certificate [RFC5280] corresponding > to the key used to digitally sign the JWS. > """ > > Different parties seem to be using two different methods when calculating > this field. > > *Method 1:* > > 1. Take DER encoding of the certificate which produces a 32 byte array > 2. Take the base64 url encoding > > In this method, we compute this "x5t#S256" parameter by directly url > encoding the 32 byte array without taking the hex string. Example given at > appendix A of the MTLS token spec [2 > <https://datatracker.ietf.org/doc/html/rfc8705#section-appendix.a>] > appears to be following this method. > > *Method 2:* > > 1. Take DER encoding of the certificate which produces a 32 byte array > 2. Convert it into a hexadecimal string and transform it into a 64 byte > array > 3. Take the base64 url encoding > > In some places I have seen the following approach is used to obtain a > value equal to the "x5t#S256" field. > > 1. Display the certificate with a tool like Keytool Explorer and copy the > SHA 256 fingerprint. > 2. Remove colons (":"s) and convert it to all lowercase. > 3. Base64url encode the value. > > This approach requires the above hexifing step (method 2) in order to > produce a similar result when computing the "x5t#S256" field. > > Hence I would like to query about the correct approach to follow when > calculating the "x5t#S256" parameter. Or can we accept both these forms as > correct methods to calculate the mentioned field? > > Thanks in advance. > > [1] https://datatracker.ietf.org/doc/html/rfc7515#section-4.1.8 > [2] https://datatracker.ietf.org/doc/html/rfc8705#section-appendix.a > > Best Regards, > Thamindu Jayawickrama > > -- Best Regards Thamindu Jayawickrama B. Sc in Engineering (Hons) Department of Computer Science & Engineering University of Moratuwa +94 71 485 2364 | +94 77 512 7790
_______________________________________________ OAuth mailing list OAuth@ietf.org https://www.ietf.org/mailman/listinfo/oauth
