Re: [TLS] NULL cipher to become a MUST NOT in UTA BCP

Ralph Holz <holz@net.in.tum.de> Wed, 03 September 2014 18:00 UTC

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Date: Wed, 03 Sep 2014 20:00:43 +0200
From: Ralph Holz <holz@net.in.tum.de>
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Subject: Re: [TLS] NULL cipher to become a MUST NOT in UTA BCP
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>> That will make it clear that implementers are free to retain NULL (and
>> they will), but that the purpose of the BCP is to propose secure TLS
>> configurations to protect application-layer protocols, and for those no
>> deployment should ever negotiate NULL.
> 
> This is still too strong.  Local MTA to Mail-Store LMTP is an
> application protocol.  It is a fine use-case for NULL ciphers.

I hear you (and the others), but balancing the purpose of the BCP with
such requirements as you mention leads me to believe we should favour
the solution I proposed. I added one more thing, though:

"Note: TLS implementations MAY retain code for the NULL cipher to allow
specialised purposes like debugging, custom solutions, etc."

That "custom solution" - to me - seems to address what you describe. I
see no other way to balance the requirements.

If the vote were black/white between dropping and keeping, I'd favour
dropping, by the way. I'd rather protect the many.

Ralph

-- 
Ralph Holz
I8 - Network Architectures and Services
Technische Universität München
http://www.net.in.tum.de/de/mitarbeiter/holz/
Phone +49.89.289.18043
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