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RE: Making Implicit C-E work.

From: <K.Morgan@iaea.org>
Date: Wed, 14 May 2014 07:34:43 +0000
To: <jgraettinger@chromium.org>, <matthew@kerwin.net.au>
CC: <grmocg@gmail.com>, <ietf-http-wg@w3.org>, <C.Brunhuber@iaea.org>
Message-ID: <0356EBBE092D394F9291DA01E8D28EC20112D9C44F@sem002pd.sg.iaea.org>
On Tuesday,06 May 2014 23:11, Johnny Graettinger wrote:

> Something that hadn't been clear to me until now (thanks Roberto) is a significant difference

> between implicit c-e: gzip and implicit t-e: gzip …


> Assume a gateway inter-mediating a HTTP/2 client and a HTTP/1.1 origin. When forwarding

> a POST from the client which uses c-e: gzip … it's reasonable for the gateway to forward the

> request and expect the client to know what it's doing.


> Conversely, when forwarding a POST from the client which uses t-e: gzip, the gateway is

> required to decompress before handing off to the origin … and face the ensuing DoS attack

> surface.

(This thread is about implicit C-E gzip for responses. C-E gzip on requests is being discussed in the thread “Support for gzip at the server #424”.  No matter though, because your example is true in the other direction as well. Plus, t-e gzip is in both directions.)

Nearly all of the problems brought up w.r.t. t-e gzip are also true for C-E gzip. This one is no exception.

Implicit C-E gzip adds a large DoS attack surface to intermediaries.  An attacker simply sends requests without ‘accept-encoding: gzip’ from a HTTP/1.1. origin through a 1.1<->2 gateway for a resource it knows the server will implicitly C-E gzip. Then (using your own words Johnny) “the gateway is required to decompress before handing off to the origin … and face the ensuing DoS attack surface.”

*I would be thrilled if a request with no ‘accept-encoding’ header implied C-E gzip, but you can opt out by explicitly sending an ‘accept-encoding’ header.*

Just as a point of clarification, I don’t think t-e gzip should be implicit.  (I may have said that in the past, but definitely changed my mind for the very reason you brought up.) I do think frame compression (t-e gzip) and its associated SETTINGS_COMPRESS_DATA setting should be enabled by default, but I think there should always be a way to opt out.

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Received on Wednesday, 14 May 2014 07:35:27 UTC

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