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seen Sep 12 '13 at 18:19

Oct
1
comment Online backup : how could encryption and de-duplication be compatible?
The second attack, which we call "learn the remaining information", is not so obvious, and as far as I know nobody was aware of this attack until 2008 when Drew Perttula and Brian Warner developed it as an attack against the Tahoe-LAFS secure filesystem. In the "learn the remaining information" attack, the attacker can make guesses about a few secret, random, unknown parts of a larger file and then find out if one of their guesses is correct. Please see the write-up at: tahoe-lafs.org/hacktahoelafs/drew_perttula.html
Oct
1
comment Online backup : how could encryption and de-duplication be compatible?
There are two possible attacks. The first one, which we call the "confirmation of a file attack" is the obvious problem that deduplication exposes the fact that the two things were the same as each other. This issue was immediately appreciated and discussed when convergent encryption was first proposed (not under that name) on the cypherpunks mailing list in 1996. (Before Microsoft applied for a patent on convergent encryption, so the cypherpunks discussion is prior art that invalidates the Microsoft patent.)