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From Paul Querna <p...@querna.org>
Subject Re: [PROPOSAL] mod_cloudbeat
Date Mon, 30 Mar 2009 15:18:03 GMT
On Mon, Mar 30, 2009 at 5:10 PM, "Plüm, Rüdiger, VF-Group"
<ruediger.pluem@vodafone.com> wrote:
>> -----Ursprüngliche Nachricht-----
>> Von: Paul Querna
>> Gesendet: Montag, 30. März 2009 17:04
>> An: dev@httpd.apache.org
>> Betreff: Re: [PROPOSAL] mod_cloudbeat
>>
>> On Mon, Mar 30, 2009 at 4:45 PM, Jim Jagielski
>> <jim@jagunet.com> wrote:
>> >
>> > On Mar 29, 2009, at 11:43 AM, Paul Querna wrote:
>> >>
>> >> URL Authentication is done by computing an randomly seeded
>> md5 signature
>> >> of:
>> >>    seed + "$"+ MD5(seed + shared_secret + uri)
>> >> This is base64 encoded, and placed in a 'X-Cloudbeat-Auth' header.
>> >>
>> >
>> > Thinking outloud here... The idea I think is to ensure that
>> > the X-Cloudbeat-Auth defines an authenticated server, using
>> > the fact that it knows the shared secret. But how does the
>> > above do that? Say for example that A and B known to each
>> > other and B is sending X-Cloudbeat-Auth. This is easy to
>> > find out, of course. So I setup B' to send the exact same
>> > header and apply a DoS to B causing it to drop/hang/whatever.
>> > Won't A just see B' as B, maybe thinking that it had a
>> > momentary glitch and came back? It seems to me that we need
>> > some sort of IP:port knowledge in there as well.
>>
>> In my mind, URL includes the IP/port, so you shouldn't be able to DoS
>> it this way.  I guess I should of been clearer by what I meant with
>> URL.
>>
>> I was thinking about this more, and we should also change the hash to
>> sha1, considering it only takes a few days to find md5 collisions if
>> you have enough playstation 3s:
>>     seed + "$"+ sha1(seed + shared_secret + ip ":"+ port + URI)
>
> Which IP do you use here? The one from the client that sends the request?
> Furthermore we should include a timestamp as we are very vulnerable against
> replay attacks otherwise.

Server A wants to talk to B.

We include server B's IP in the hash that Server A sends to B.  (this
prevents B without knowledge of the secret from doing a replay).

I dislike adding a timestamp as it tends to make the protocols more
brittle, but maybe int(current unix timestamp / 2 days in seconds)
would allow boxes out of sync, but prevent long term replay and hash
reuse.

Thanks,

Paul

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