Re: Checksum (Re: KINK issue list)

On Jan 27, 2005, at 03:16, KAMADA Ken'ichi wrote:
> With regard to these three issues, I'd propose using HMAC as a KINK
> checksum.
> According to kcrypto, each etype based on simplified profile and
> etype based on 3DES has a HMAC as its attribute.  Let's use it as is.
> DES-based etypes (des-cbc-md5, des-cbc-md4, and des-cbc-crc) have
> no HMAC associated with them, so use HMAC-MD5.
>
> My main concern with this proposal is whether all future etypes
> will be based on simplified profile (have HMAC, I mean) or not.

I think it's safe to say that eventually we will see new encryption 
types that do not use the simplified profile.  We may also see some 
that do, of course.  But with the variety of authenticated-encryption 
modes being produced and analyzed, it would make sense for us to stop 
constructing our own.  So I'd expect some future cryptosystem to be 
based on EAX, CCM, or some other such mode.

In order for KINK to not require updates for these future 
cryptosystems, you'd need to be able to say now how to determine what 
kind of checksum is to be used.

The only tricky issue in dealing with the required-to-implement 
checksum type should be the lack of a fixed size output.  Is it that 
hard to work around?  (Maybe omit the checksum field when computing the 
checksum?)

Ken