Re: [Grapevine-devel] Re: Grapevine commentary

[Anthony J. <aj...@cl...>]

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On Friday 31 October 2003 16:13, Stephen Blackheath wrote:
> Thanks for all that.  How can the client check the signature?  What
> prevents the node with the root file from lying, since this information
> can't be protected by a CHK?

The client can decide whether or not to believe the signature. The signature 
must be from a node in the area at or near where the root file is located. A 
client should require a certain number of signatures from that area before it 
will actually believe them and not try to find the file for itself.

> Another idea I had was this:  Let's say the file contains 100 blocks.  You
> do a random sample to see what proportion of those blocks can be fetched
> (without downloading - it would be good find a way to cryptographically
> prevent cancer nodes lying).  A statistical analysis will give you a
> reasonably accurate indication of the probability of retrieving the entire
> file, with only a small sample.

That idea works. It certainly had the advantage of simplicity.

> Your plan has an efficiency advantage, though the signing would consume CPU
> time.  The idea I just mentioned has the advantage of simplicity - a very
> important thing to me at the moment.

The signing only happens when the node discovers that a file is broken. After 
that the "this is broken" marking can gain or loose signatures. I can see 
this starting to get complicated. I think I'm starting to prefer your idea.

Anthony
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