Re: [kitten] Verified authorization data

[Peter Mogensen <[e-mail]>]

On 2014-06-12 15:01, Simo Sorce wrote:
> Yes, we decided to combine this protection with ticket binding in one
> single operation by using EncTicketPart in the MAC calculation, makign
> the CAMMAC *simpler* to build.

I must have misunderstood something fundamental then.

The draft says:
"the KDC computes the MAC in the kdc-
       verifier over the ASN.1 DER encoding of the EncTicketPart of the
       surrounding ticket, *but* where the AuthorizationData value in the
       EncTicketPart contains the AuthorizationData value contained in
       the CAMMAC instead of the AuthorizationData value that would
       otherwise be present in the ticket."

(My emphasis)

So it's not the actual EncTicketPart which is used for the MAC. It's 
another version with different AuthorizationData. You have to compute 
both versions.
Compared to simply just placing the kdc-verifier outside of the 
EncTicketPart and using the actual EncTicketPart for computing the MAC.
... which I know can give compatability problems, but just so we 
understand what each other is talking about.

I would intuitively think it was simpler to just sign the entire actual 
EncTicketPart with the kdc-verifier. Of course, that will then bind to 
also any other authdata in the ticket.

/Peter