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From: Maaartin on 16 Mar 2010 18:20
On Mar 16, 6:12 pm, Christian Baer <christian.b...(a)uni-dortmund.de>
wrote:
> On Tue, 16 Mar 2010 09:23:15 -0700 (PDT) Maaartin wrote:
> > Sure, and there's a nice algorithm for this: secret sharing. I know
> > only the one by Shamir, which is quite easy to implement and proven do
> > it its job perfectly. But I don't know if there's a disc encryption
> > software integrating a key sharing algorithm.
>
> You can always use more than one key file and each operator holds one.
> Basicly, if they want to conspire against you, there is no real technical
> way to stop them doing that.

But this is only a trivial way of key sharing - you require all of the
keys. This is most secure w.r.t. privacy but also the most dangerous
w.r.t. key loss. If any of the key holders is gone (dead, lost,
drunken, forgetful, ...), you're toasted.

The other extreme would be to accept any of the keys. A simple usage
of key sharing is to require K of N keys, which means there's no data
leak unless K keyholders co-operate und no data loss unless N-K of
them are gone. And you don't have to wake up the whole crew after each
power outage. There're more sofisticated scenarios where you can
preciselly specify which key subsets are sufficient.
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