Laurence, Any statements relating C509_Data and c5t should just reaffirm that the content of the C509_Data bstr is exactly the same as the input to the thumbprint hash. The c5t can be computed or compared without needing to decode or care about the C509Certificate structure.
On Tue, Jul 21, 2026, 16:20 Laurence Lundblade <[email protected]> wrote: > Here’s text from C509: > > The value type of c5t is the COSE_CertHash structure defined in > [RFC9360], which contains the hash value > of the C509 certificate calculated over C509Certificate. Thus, > C509CertData contains all data necessary > to calculate the thumbprint c5t. > > Later the table says: > > c5t 22 COSE_CertHash Hash of a C509Certificate > > I think this means that the first byte input to the hash is 0x8B, not 0x59 > (0x59 is the first byte of an encoded byte string of length 256..64K) > because of the mention of C509CertData. > > Seems like the definition should be: > > The input to the hash is a CBOR-encoded C509Certificate. > > No need to mention C509CertData because it’s not a factor in the c5t, only > in c5b and c5c. > > LL > > _______________________________________________ > COSE mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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