>> "The RSA algorithm gives security under the assumption that as long as >> the private key is private, you can't break in unless you guess it. >> We've shown that that's not true," said Valeria Bertacco, an associate >> professor in the Department of Electrical Engineering and Computer >> Science, in a statement. > > They're not the first ones to show that! Side-channel attacks have been > around for a while now. It's not just the algorithms, but the machine > executing them and its physical characteristics that matter.
I agree. I think the paper overstates its novelty and implications. It seems to be an experimental implementation of a fault attack presented by Boneh, DeMillo and Lipton (i.e. where it is assumed that single bit errors affect the private exponent). They target _some_ crypto application** that uses the openssl library running on an fpga board. Getting the attack to work in real life is no small feat, so they deserve props for that, but they make a few questionable claims -- e.g. they seem to state that the left-to-right fixed-window exponentiation algorithm was thought to be immune to fault attacks. In fact, adapting the BDL attack, which was presented against a right-to-left algorithm, to work against a left-to-right algorithm is straightforward, and so the susceptibility of the left-to-right FWE algorithm has been known for some time. What I find much more strange about the paper is that the authors make no mention of message blinding. I could be wrong, but message blinding would defeat their attack. By default, an openssl server utilizes message blinding in its private key operations, so there attack wouldn't apply... ** I just had the following realization: I had assumed that the authors were attacking an openssl *server* running on the fpga board, but perhaps that is not so. They don't seem to make that specific claim. They claim only to be attacking an "unmodiﬁed version of the OpenSSL library". It is possible that they only created a toy RSA application that generates signatures using the openssl library (i.e. by making calls to specific openssl functions). This would explain why they don't discuss message blinding -- because they didn't enable it in their toy application! I suspect that's what they did. In that case, their experimental results say very little about the susceptibility of an openssl server to fault attacks. Wow... if I'm correct, then the authors really need to be more clear about exactly what they did. -James
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