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

Paul Lambert <paul@marvell.com> Tue, 02 September 2014 21:01 UTC

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From: Paul Lambert <paul@marvell.com>
To: "tls@ietf.org" <tls@ietf.org>
Date: Tue, 02 Sep 2014 14:01:22 -0700
Thread-Topic: [TLS] NULL cipher to become a MUST NOT in UTA BCP
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Subject: Re: [TLS] NULL cipher to become a MUST NOT in UTA BCP
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]-----Original Message-----
]From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Viktor Dukhovni
]Sent: Tuesday, September 02, 2014 12:52 PM
]To: tls@ietf.org
]Subject: Re: [TLS] NULL cipher to become a MUST NOT in UTA BCP
]
]On Tue, Sep 02, 2014 at 09:47:08PM +0200, Ralph Holz wrote:
]
]> > Postfix supports authenticated NULL ciphers for communication
]> > between an MTA and local (127.0.0.1 or ::1) LMTP server.  Encrypting
]> > local IPC is just a waste of CPU.  Yes, this is a specialized use-
]case.
]> >
]> > This can also be useful for access-controlled hand-off between
]> > reverse HTTP proxies, and web applications that support client
]> > certificates.  These are sometimes used to implement GSSAPI SPNEGO
]> > support in front of application that don't support GSSAPI.  The
]> > application is configured to listen on 127.0.0.1, but is then
]> > vulnerable to impersonation attacks from anything running on the
]> > host.  With authenticated NULL ciphers, the connection can be
]> > restricted to just the front-end reverse proxy.
]>
]> Both seem to be real corner cases - wouldn't they be covered just as
]> well with encryption prescribed?
]
]Yes, these are "corner cases".  A sufficiently broadly applicable tool
]has a lot of corners.
]
]While I agree that NULL ciphers should not be enabled *by default*,
]making NULL ciphers a "MUST NOT" seems rather too strong.  Why burn
]limited CPU cycles doing nothing useful (encrypting local IPC).

I disagree, and support the draft as written.  
'MUST NOT' is the appropriate recommendation for NULL ciphers.

Paul


]
]--
]	Viktor.
]
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