Subject: RE: [TLS] Re: PSK question

From: [email-masked]
Date: Wed, 15 Dec 2004 11:40:19 +0200

[email-masked] writes:
> EKR <[email-masked]> writes:
> 
> > Peter, do you have a strong objection to this proceeding 
> > as-is or do you just find it mildly unaesthetic?
> 
> I'm not keen on the PSK kludging when it's fed into the PRF
> but I guess I can live with that, however I'd really like to
> have the server keyex/identity hint made optional.  Except for
> one extremely obscure situation (the 3GPP thing that Pasi
> mentioned), implementors won't even know what they're supposed
> to do with this facility, let alone be able to use it.  All
> it's doing is unnecessarily complicating the code on both the
> client and server, and bloating up the handshake message size.

It should not complicate the client code at all, since even if
the client does not use the hint for anything, it has to be able
to skip it. And the "bloat" we're talking on server side is maybe 
one line of code.

So IMHO it really does not matter either way (reducing message
bloat by 6 bytes increases specification bloat by a couple of
sentences), so if this is keeping the draft from going forward,
let's change it.

In Section 2, change

   "To help the client in selecting which identity to use,
   the server can provide a "PSK identity hint" in the
   ServerKeyExchange message (note that if no hint is 
   provided, a ServerKeyExchange message is still sent)."

to

   "To help the client in selecting which identity to use,
   the server can provide a "PSK identity hint" in the
   ServerKeyExchange message. If no hint is provided, 
   the ServerKeyExchange message is omitted."

In Section 2, change

   "The elements in parenthesis are not included when PSK 
   key exchange algorithm is used."

to

   "The elements in parenthesis are not included when PSK
   key exchange algorithm is used, and "*" indicates a
   situation-dependent message that is not always sent."

In the figure in Section 2, change 

  "ServerKeyExchange"

to
  
  "ServerKeyExchange*"

In Section 3, change

   "When these ciphersuites are used, the ServerKeyExchange and
   ClientKeyExchange also include the Diffie-Hellman parameters.
   The PSK identity and identity hint fields have the same
   meaning as in the previous section."

to

   "When these ciphersuites are used, the ServerKeyExchange and
   ClientKeyExchange messages also include the Diffie-Hellman
   parameters.  The PSK identity and identity hint fields have
   the same meaning as in the previous section (note that
   the ServerKeyExchange message is always sent even if no
   PSK identity hint is provided)."

In Section 4, change

   "As in normal RSA ciphersuites, the server must send a
   Certificate message.  The format of the ServerKeyExchange
   and ClientKeyExchange messages is shown below."

to

   "As in normal RSA ciphersuites, the server must send a
   Certificate message.  The format of the ServerKeyExchange 
   and ClientKeyExchange messages is shown below.  If no PSK 
   identity hint is provided, the ServerKeyExchange message 
   is omitted."

Would this be better?

Best regards,
Pasi

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---

From: Eric Rescorla <[email-masked]>
Date: Wed, 15 Dec 2004 11:07:06 -0800

> sentences), so if this is keeping the draft from going forward,
This looks good to me. Peter, can we call this soup?

-Ekr