<snip> Watermarking is an attack which does not give any secrets to the attacker but allows him to prove that the user of the encrypted file system has a certain file stored on his drive. The file has previously been specially prepared by the attacker. Following [1], data encrypted with the CBC cipher mode is vulnerable to watermarking attacks under some circumstances. Consider a file which is divided into file blocks B1 , ..., Bk of blocksize which are individually encrypted using CBC and AES (whereas each file block consists of blocksize/16 cipher blocks) (as in EncFS). The attack succeeds if the attacker is able to calculate the XOR of the initialization vectors (IV) for some Bi and Bj , i != j. If so, the attacker prepares the first plain text blocks of block i and j such: Pi1 XOR Pj1 = IV(i) XOR IV(j) and therefor Pi1 XOR IV(i) = Pj1 XOR IV(j) This causes that Ci1 = Enc(Pi1 XOR IV(i)) = Enc(Pj1 XOR IV(j)) = Cj1 i.e. the first cipher block of file blocks i and j are identical. Therefore, the attacker can test the cipher blocks Ci1 and Cj1 and conclude with high probability whether this is his prepared file or not. We analyzed the distribution of IV(i) XOR IV(j) for a randomly chosen blocks and a random so-called fileIV which is used to make the IVs different from file to file. This showed that IV(i) XOR IV(j) is not at all uniformly distributed. There is a certain value for IV(i) XOR IV(j) which is highly more probable that expected for a uniform distribution (2*10^-4). We then watermarked a file such that the even file blocks start with the found value and the odd file blocks with all zero. So, the encrypted file is successfully recognized by testing whether there are two consecutive file blocks that start with the same cipher block. Using a file with 50000 blocks we achieved a probability of > 99.9% of recognizing the watermarked file. </snip>
EncFS 1.7.1 -- August 30, 2010 Change Log * add new IV initialization mode to foil watermark attack - see this 2010-08 analysis. The old IV setup is kept for backwards compatibility.
Arch's: Test & stabilize =sys-fs/encfs-1.7.1
x86 stable
amd64 done
GLSA Vote: no.
GLSA Vote: no -> Closing. Feel free to reopen if you disagree.
