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Thats not true. Every time when you hash something what is bigger
than your returned hash, there can be collision.
This hash thing was talked alot before and in that time I offered
solution that first slice that message to small parts and then select example
first and last part. Hash both of them and thats it, almost impossible to get
collision. It's still possible, but change is very very
small.
So to be safe, there must be at least 2 full
hash.
Maybe, composite 2-column unique key (mime part size) and (mime
part SHA1/any other hash) is a suitable solution?
Same hash for
same message size is really impossible, but for
different message size it can occur.
> Date: Fri, 28 Dec 2007 18:17:46 +0100
> From:
paul nfg.nl
>; To: dbmaildbmail.org
> Subject: Re: [Dbmail] Re:
DBMail 2.3.0 released
>
> Matija Grabnar wrote:
>; >
Aaron Stone wrote:
>; >> I'm a big fan of double digest. I don't
think the algorithm matters much,
> >> just as long as the two are
very different. Even just MD5 and SHA1 should
>; >> be plenty good,
IMHO.
> >>
> > No, not more than some checksum that was
as long as the sum of the two
> > checksums you were using.
>;
> I've decided to offer some relief for those concerned. I'm
adding
>; libmhash as a build requirement, but that will add a lot of
hashing
> algorithms.
>
> By default dbmail will use SHA1
hashing for generating unique-ids per
> mime part. But dbmail will
support using any algo supported my mhash,
>; and you'll be able to do
single or double digests, and you can select
>; the hash(es) you trust
not to generate collisions. Of course, after you
> change the hash(es)
the ids in the mimeparts and partlists tables will
> have to be
recalculated and updated, so dbmail-util will have to support
> that.
And it will be up to the DBA to make sure the ID fields are wide
>
enough to hold the keys.
>
>
>
>
>
>
--
>
________________________________________________________________
> Paul
Stevens paul at nfg.nl
>; NET FACILITIES GROUP GPG/PGP:
1024D/11F8CD31
> The
Netherlands________________________________http://www.nfg.nl
>
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