Subject: Re: Working Group Last call - draft-ietf-cat-kerberos-set-passwd-05.txt - non-ASN.1 comments :-)

From: Wyllys Ingersoll <[email-masked]>
Date: Tue, 22 May 2001 22:04:22 -0400 (EDT)

>> >I'm sort of stumbling around in the dark here, not being any sort of
>> >cryptographer, but I've definitely gotten the impression that not all
>> >encryption schemes use dense key spaces, and whatever other
>> >representations are used may not be trivial to convert back and forth
>> >to a random bit-string of a fixed length.  (Look at PDM: The hint is
>> >desirable because finding the prime may be an expensive operation.)
>> 
>> The idea is for the server to add enough entropy to the keys. Exactly
>> what should be done for each different encryption type is a function of
>> the encryption type.
>
>What about adding a new request type just to get random data (entropy)
>from the server? The request would have one argument: requested length
>of random bit string. The server would respond with a bit-string of upto
>that many bits, possibly fewer, including possibly 0 (to allow for
>situations where the server can't generate sufficient entropy).
>
>It would be up to the client to obtain enough entropy by whatever
>method it prefers (including asking the server for some) and then
>generating a key from it.
>
>As long as there is no set-me-a-new-random-key-and-tell-me-what-it-is
>request type then this business of adding entropy to a key seems a bit
>overdone such that a separate request to get random data from the
>server seems to me like a clearer approach, but, then again, I'm no
>cryptographer.
>
>So that makes it three request types:
>
> - change password
> - set key
> - could you spare me some entropy?

I dont think this request type belongs in this draft.  Its use could
go way beyond just the password set/change functionality that this
draft is supposed to address.  Im not even sure it belongs as part 
of Kerberos at all since providing entropy is just a general
cryptographic function.   It should almost be part of the OS that any
application can use, in fact some OS now offer entropy/random 
interfaces such as /dev/random for just this reason.

-wyllys

---

From: Nicolas Williams <[email-masked]>
Date: Wed, 23 May 2001 10:26:32 -0400

Indeed, but, it's already in the draft. I.e., the draft already has an
option for the client to ask for entropy as part of the set key
operation and so on and that has led to some argument as to the
semantics of it all. And what I'm arguing now is that it would be better
to separate the request for entropy because that then simplifies the
rest of the protocol and clarifies the meaning of having the server add
entropy to the client's suggested key (by getting rid of that).

Nico

--