> From: Poul-Henning Kamp [mailto:phk@phk.freebsd.dk] > Sent: Wednesday, 07 March, 2012 11:33 > > In message <0AB4526732901E45B9B3A55FFD725D67019CBB16@AUS- > EXCHANGE.microfocus.co > m>, "Michael Wojcik" writes: > > >> You cut and paste the link, and anybody who receives it can view > >> the copyrighted object, and you have no idea who leaked it. > > > >Actually, I think it's potentially worse than that. Consider this > case: > > > >- Publisher puts 100 copies of each resource on CDN, each encrypted > with > >a different key. > > What you propose is what's called "Thatcherizing" a document: During > the Thatchers government, they tweaked the spacing in a confidential > memo so that each recipients copy were unique, in order to expose > who leaked it to the press. It's similar, yes, and also similar to various proposed "Birthday Paradox" attacks against digital signatures using too-short digests (where you vary whitespace until you produce an image collision), etc. The real idea here, though, is that rather than giving every user a unique key, you partition the keyspace for each resource, so an accumulation of leaked keys gives increasing probabilistic identification of the source of the leak. > It is however, not an argument for the circus-crypto og http+aes Of course not - I meant it as an argument *against* http+aes. That's why I wrote "potentially worse" above. -- Michael Wojcik Technology Specialist, Micro Focus This message has been scanned by MailController - portal1.mailcontroller.co.ukReceived on Wednesday, 7 March 2012 17:17:27 UTC
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