Im only speculating but perhaps the hashes are generated pre-encrypt.
Although 2 identical files encrypted with the same key and no cypher
block chaining or different salts will of course generate the same
result.  But as I say, it might be a step before encrypt that then
talks to the backup server.  I guess this could be implemented in
various ways with various products.

On Mar 6, 2:29 am, Sebastian Himberger
<[email protected]> wrote:
> What I don't understand: If the encryption happens on the client side
> and is done right this shouldn't be possible, right? Or am I missing
> something? I'm certainly no expert on this.
>
> Please enlighten me.
>
> Thanks,
> Sebastian
>
> On Mar 3, 4:55 am, Karsten Silz <[email protected]> wrote:
>
>
>
> > Hi,
>
> > During the episode the Posse talked about how to reduce the data for
> > online backups by avoiding redundant files.  This is called "data
> > deduplication" and is already used in backup and email 
> > systems:http://en.wikipedia.org/wiki/Data_deduplication
>
> > I would assume most online backup systems use this.  They even mention
> > the case where during a backup a client wouldn't send a file to the
> > server if it's already there (http://en.wikipedia.org/wiki/
> > Data_deduplication#Client_backup_deduplication).

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