Re: [TLS] How ALPN makes the http2-tls-relaxed option less secure, compared to NPN (was Re: ALPN concerns)

Martin Thomson <> Tue, 10 December 2013 17:03 UTC

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Date: Tue, 10 Dec 2013 09:03:07 -0800
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From: Martin Thomson <>
To: Brian Smith <>
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Cc: Peter Gutmann <>, "<>" <>
Subject: Re: [TLS] How ALPN makes the http2-tls-relaxed option less secure, compared to NPN (was Re: ALPN concerns)
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On 9 December 2013 18:15, Brian Smith <> wrote:
> If the server really doesn't care about the security or privacy
> properties of a resource, then it wouldn't implement opportunistic
> encryption in the first place, unless it was doing so purely as a
> compatibility hack.

I don't know that hack is the right word here.

One of the options that is being considered for HTTP/2.0 is the
mandatory implementation of unauthenticated TLS for http: URIs.  If
that were the case, all that a server would have to do is upgrade
their stack.  That sets a pretty low bar.

> we'd say that the client MUST NOT advertise
> the http2-tls-relaxed ALPN token, in order to avoid tipping off any
> MitM that the connection will be unauthenticated.

Yes, but that isn't the reason I'd use for it.  The reason is that
it's not necessary.  It's got absolutely nothing to do with tipping
anybody off.