→ hack.lu CTF Power security tokens

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Having trace.pkl file and title with keyword "power" we know thats it's an Power Analysis task. In task said it's an signature generation function, by task name keyword "tokens" we can assume it's RSA.

If we plot some of our data list, we get something like: click to zoom
Can you see impulses?

Main idea of Power analysis is that different instructions have different power consumption patterns.
RSA signature generation:
S = M^d mod N


for i =L-1 downto 0:
    S = S^2 mod N
    if di == 1:
        S = S * M mod N
For every bit of d we've square and if bit = 1 we've multiplication also. So we just check our data for duration patterns:
short+long=1, short=0. Simple, hah?

Sources included.
Thanks to @hellman1908 for error corection!

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This page contains a single entry by kyprizel published on September 21, 2011 7:38 PM.

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