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[Gnu-arch-users] Re: RFC: arch protocol, smart server, and tla implement


From: Chris Gray
Subject: [Gnu-arch-users] Re: RFC: arch protocol, smart server, and tla implementation prototypes
Date: Fri, 06 Feb 2004 14:59:56 -0800
User-agent: Gnus/5.1002 (Gnus v5.10.2) Emacs/21.2 (gnu/linux)

On 6 Feb 2004, Robert Collins wrote:
> On Sat, 2004-02-07 at 06:36, Chris Gray wrote:
>> On 6 Feb 2004, Robert Collins wrote:
>>> On Fri, 2004-02-06 at 10:48, Chris Gray wrote:
>>>
>>>> My message was that skiplists are a data structure that you
>>>> should consider for reasons of efficiency, simplicity, and size.
>>>> I feel they would be preferable to what we have now and easier to
>>>> implement than a truly smart server.
>>>
>>> They're cute and all, but while talking smart client, dumb server
>>> implementations, how do you propose maintaining signatures?
>>
>> I hadn't thought of it at all.  However, committing a summary delta
>> should not be any different than committing a patchset, so the
>> signature maintenance should not be much harder.
>
> You'r proposing we keep a single patch delta regardless, so the
> summary deltas are just extra information? Or are you proposing we
> re-sign chunks of the archive on a regular basis?

The summary deltas are redundant information.  They can certainly be
signed.  I don't know how the signing mechanism works in arch right
now, so I don't want to say what the exact signing mechanism for
summaries will be.  The way I imagine it is that there is a command
that says "I added this file to the archive, add its signature."
Well when you add a summary delta, run that command.

> I.e. in a shared archive Tom commits base-0, patch-1 -> patch-9 in a
> version. And I commit patch-10, causing a rebalance of the skiplist,
> will those summaries be signed by me or Tom? 

I'd say it's debatable, but my guess is that when the debate is over,
the changeset would be signed by you.  You are responsible for the
last change in the summary.

> How will someone who
> wants to check my commits only be sure that whats in the summaries
> is the same as whats in the single patch deltas?

How can someone be sure that the single patch deltas are what you
intended to be committed?  By checking the signatures, all he sees is
that you uploaded such-and-such a file with so-and-so bytes.  He can't
know that the patch has been computed correctly.  If each summary
delta is signed, the same assurances are there.  That is, this hunk of
data is what was been uploaded by you.  So just signing the data is no
assurance that the data is valid.

This is not to say that it wouldn't be trivial to check if summaries
are valid.  Simply replaying the summary and the individual patches to
different trees and doing a "diff -r" would work.

Cheers,
Chris





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