Re: [freehaven-dev] Deletion of documents

[dmolnar@belegost.mit.edu]

Brian raised another issue at the meeting today :

* The y values are public, so other people can incorporate the y value 
  from one share as the self-destruct code for another, completely
  unrelated share. This allows two things :

	1) A publisher can be "linked" to a share which he did not 
	actually publish. Suppose Roger publishes crypto-anarchist
	tracts with a certain value of y. I can create a share of
	kiddie porn with the same value of y and distribute it widely.
	When the State raids Roger looking for subversive material,
	they find that his value of x also unpublishes some kiddie porn. 

	This is either good or bad, depending on how it's interpreted
	legally 
		- good : because someone can do this, it raises reasonable
		doubt about Roger publishing kiddie porn 

		- bad : it doesn't raise enough doubt to get Roger 
		off the hook.

	2) We can have situations in which a single self destruct code
	destroys lots of unrelated data. Some of which we may want to 
	keep. This is no problem if we know ahead of time what data
	corresponds to what y value - we can pull it out and submit with
	a new y value.

	If we don't know, and we release an x value...

	We might then want something which retreives shares based on
	what y value they have. This wouldn't completely solve the
	problem, since between the last time we check and the time
	we release x, some new data may be added. 


These properties do not seem to arise with the "unpublish requests signed
by same private key used to sign shares." This is because no one other
than the original publisher has the private key, and therefore cannot
cause any new shares to be unpublish-able by means of that key. 

Thanks, 
-David


On Sat, 11 Mar 2000, Ron Rivest wrote:

> 
> Why not just publish a value y=SHA1(x) with a document.  y could exist
> with each share.  When x is revealed, anyone holding a share with
> "self-destruct code" y should delete their share...
> 
> 	Cheers,
> 	Ron
>