http://www.techworld.com/security/news/index.cfm?newsID=105263 By John E. Dunn Techworld 03 October 2008 Bitmaps stored inside encrypted backup files could be vulnerable to a sophisticated 'comparison' attack, a German security researcher has discovered. In a new paper, Bernd Roellgen of Munich-based encryption outfit PMC Ciphers, explains how it is possible to compare an encrypted backup image file made with almost any commercial encryption program or algorithm to an original that has subsequently changed so that small but telling quantities of data 'leaks'. The problem is that bitmaps often display low levels of entropy, such as would be the case in pictures taken at night with large areas of high contrast. Roellgen's attack is based on comparing two volumes encrypted into scrambled ciphertext using the same symmetric or 'static' key, where the original subsequently has new files added. This yields a pattern of structured similarities and differences that can be used to reveal some of the original information in plaintext form. The attack doesn't work for other types of data, for instance text files, because the entropy levels are too high. But it is believed to effect almost any encryption program currently on sale as long as the two volumes being compared use the same encryption key whilst being slightly different from one another. [...] __________________________________________________ Register now for HITBSecConf2008 - Malaysia! With a new triple-track conference featuring 4 keynote speakers and over 35 international experts, this is the largest network security event in Asia and the Middle East! http://conference.hackinthebox.org/hitbsecconf2008kl/Received on Sun Oct 05 2008 - 23:20:02 PDT
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