Re: [pkix] draft-turner-additional-methods-4kis to ISE

[[e-mail] (Martin Rex)]

Sean Turner wrote:
> 
> Manger, James H wrote:
>> A few comments on "Additional methods for key identifiers":
>>
>> Truncation: are the "least significant bits" of a hash the
>> right-most bits? I would have though keeping the leftmost bits
>> was slightly more intuitive.
> 
> I'll add "(i.e., leftmost)" after "least significant bits".

"leftmost bits" is also what NIST FIPS 186-3 (Digital Signature Standard)
uses for hash output truncation (Section 4.2, page 16):

                                                   When the length of the
   output of the hash function is greater than N (i.e., the bit length of q),
   then the leftmost N bits of the hash function output block shall be used
   in any calculation using the hash function output during the generation
   or verification of a digital signature.



> 
> I'll add a new section:
>
>   [...]
>
> The SHA-256 hash output of the key is as follows:
> 
>    E72EE6C9C63D2B7F960F0E0611B9800917B5F9494182403EF1BBA8927A57625E
> 
> Using method 1 in Section 2, the output is truncated as follows:
> 
>    E72EE6C9C63D2B7F960F0E0611B9800917B5F949


Yup, an example helps showing truncation to "leftmost bits".


-Martin