Subject: Comments on draft-ietf-kitten-krb5-gssapi-prf-03.txt

From: Jeffrey Altman <[email-masked]>
Date: Wed, 18 May 2005 11:00:56 -0400

Overall I believe this document is ready for last call.   I do have one
concern though.  In the Security Considerations a technical unit of
measurement is used for which I am aware of no agreed upon standard
definition, the "handful".  I do not feel comfortable with a Security
Consideration that recommends a pinch of this and a touch of that.

Jeffrey Altman

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From: Jeffrey Hutzelman <[email-masked]>
Date: Wed, 18 May 2005 12:40:26 -0400

> Consideration that recommends a pinch of this and a touch of that.

I see nothing about pinches or touches; only handfuls.
I see no problem with using a somewhat vague term in this instance, since 
the point is not to make a specific recommendation that "more than X uses 
per context is bad", but rather to suggest that making a few calls per 
context is OK, but making them continuously across a long connection is not.

-- Jeff

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From: Nicolas Williams <[email-masked]>
Date: Wed, 18 May 2005 16:14:23 -0500

> I see nothing about pinches or touches; only handfuls.

Thanks for the laughs :)

> context is OK, but making them continuously across a long connection is not.

That text does need some cleanup, and the real issue is that the GSS-API
can't enforce any limits on the useful lifetime of PRF output used for
cryptographic purposes.  So, I propose replacing that paragraph with:

   Care should be taken not to exceed the useful lifetime of
   GSS_Pseudo_random() output, particularly when used for cryptographic
   purposes.  Specifically, applications should limit use of
   cryptographic keys derived from GSS_Pseudo_random() output to the
   original lifetime of the security contexts to which
   GSS_Pseudo_random() is applied.

That seems much more specific -- no handfuls, pinches or touches.

Cheers,

Nico
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From: Jeffrey Altman <[email-masked]>
Date: Wed, 18 May 2005 17:25:06 -0400

> That seems much more specific -- no handfuls, pinches or touches.

Nico:

I am much happier with the proposed text.   Does anyone else have any
comments?

Jeffrey Altman

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From: Jeffrey Hutzelman <[email-masked]>
Date: Thu, 19 May 2005 12:42:31 -0400

> I am much happier with the proposed text.   Does anyone else have any

I have no problem with adding that text, but it sounds like it addresses a 
different problem than the paragraph Nico proposes to replace.  The 
existing text appears to be concerned about the amount of data which the 
PRF can safely be used to generate.

-- Jeff