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Re: [TLS] Entirely omitting context in draft-ietf-tls-extractor

<Pasi.Eronen@nokia.com> Mon, 22 February 2010 18:05 UTC

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From: Pasi.Eronen@nokia.com
To: ekr@networkresonance.com, tls@ietf.org
Date: Mon, 22 Feb 2010 19:06:19 +0100
Thread-Topic: [TLS] Entirely omitting context in draft-ietf-tls-extractor
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Subject: Re: [TLS] Entirely omitting context in draft-ietf-tls-extractor
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Not wearing any hats: This could potentially simplify TLS library 
APIs a bit (no need to provide special cases for EAP-TLS/EAP-TTLS).  
And since we require that one label can't be a prefix of any other 
label, this seems safe, too. So no objections from me as individual.

Wearing AD hat: I'll wait for a week or so to see if there are
objections before OK'ing this change with the RFC editor.

Best regards,
Pasi

> -----Original Message-----
> From: tls-bounces@ietf.org [mailto:tls-bounces@ietf.org] On Behalf Of
> ext Eric Rescorla
> Sent: 22 February, 2010 01:35
> To: tls@ietf.org
> Subject: [TLS] Entirely omitting context in draft-ietf-tls-extractor
> 
> During LC, we received a comment from Jouni Malinen that
> unconditionally
> including the context in the PRF created an unnecesssary
> incompatibility
> with exporter-type mechanisms in EAP-TLS and EAP-TTLS which could
> otherwise
> be retconned into being extractor usages. In order to address this, I
> propose changing the text to read:
> 
> 
>   If no context is provided, it then computes:
> 
>          PRF(SecurityParameters.master_secret, label,
>              SecurityParameters.client_random +
>              SecurityParameters.server_random
>              )[length]
> 
>   If the context is provided, it computes::
> 
>          PRF(SecurityParameters.master_secret, label,
>              SecurityParameters.client_random +
>              SecurityParameters.server_random +
>              context_value_length + context_value
>              )[length]
> 
>   Where PRF is the TLS PRF in use for the session.  The output is a
>   pseudorandom bit string of length bytes generated from the
>   master_secret. (This construction allows for interoperability
>   with older exporter-type constructions which do not
>   use context values, e.g., [RFC5281]).
> 
> Any objections?
> 
> -Ekr
> 
> 
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