Slashdot Mirror
Breaking RSA Keys by Listening to Your Computer
An anonymous reader writes "Adi Shamir and crew gave a talk on preliminary results in extracting a private RSA key
just by listening to the computer!. Similar to power analysis and LED leakage, this is a non-invasive, side channel attack that may have applications to tamper-resistant systems. It appears to be related to noisy capacitors on the motherboard, an effect which has been observed when CPU power saving is enabled on laptops."
Does anyone know the range of how far you can be away from the computer to hear the sounds? The proof-of-concept website just seemed to be "look, here are pictures of computer operations... in sound! Yay!" without enlightening us on any details.
Twenty years ago at Bell Labs one of the speech machines (an SEL with homebrew audio i/o) had output to loudspeakers that went through unshielded speaker wires that ran past the CPU, so if you weren't playing anything back the speakers played back CPU noise. We could tell what stage a compilation was at by the noise that came over the speakers.
If you go to the site of the DPA attack,Cryptographic Research, you can see that they have already have patents on Systems to protect against these kind of attacks. So it's not like they have developed anything (I don't know if they have) but you can already pay them to get protection from this kind of attack! yay!
Even at a 96 kHz sampling rate, the maximum frequency that can be sampled is 44 kHz. How could one hope to extract a certain few bits from a recording when the CPU's instruction throughput is many times that? Most of the information that would need to be examined wouldn't make it onto the recording. Correct me if I'm wrong, but it seems Nyquist leaves this idea dead in the water.
If you really want to do some acoustic evesdropping, listen to the keyboard. It's got a much larger signal to begin with (from across the room, instead of having to paste your ear to the computer case.) Since there are always slight mechanical differences between keys on any given keyboard, I would think that the sound spectrum would also be slightly different. Being able to always listen in on the same user would also help, since most people are somewhat consistent regarding which finger they use on which key. (Evesdropping on people who were smart enough to take a touch-typing class in high school is also a big plus.)
Assuming you could discern between the acoustic fingerprint of 100 different keys, then it's just a matter of figuring out which sound goes with which key. It's a simple substitution cypher, which are almost trivial to break.
Sneak your cell phone into your boss's office, set it to silent mode and plug in a headset so that you can set it to auto-answer when a call comes in. Then, while your boss is busy typing dirty notes to his mistress, you call your cell phone, start recording it, and presto, you've got a keylogger without ever having touch his computer or the software on it. Then, at your next performance review, you convince him to give you a hefty raise.
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
The most common thing I've found to induce audible noise (I use a SB Live, and can easily hear this with even cheap speakers) is to demute the sound card inputs that aren't connected to anything -- like CD audio and whatnot -- and then start moving my PS/2 mouse, which generates a fairly slow sequence of signals, producing a definite buzz. Video redraw also can do this -- dragging windows works well as well, and what's on the screen (oddly enough, lots of white areas seems to cause more of a buzz) has an impact.
It's really amazing how dirty a computer power supply is -- I also picked up a headphone preamp that fits inside a 5.25" drive bay, and can optionally run off the computer power supply. If it's running off the power supply, I get a *very* noisy signal that is affected by things like hard drive access.
May we never see th
R = Ron Rivest
S = Adi Shamir
A = Len Adleman
Having worked in telecommunications as well as consumer electronics and computing, I've played a lot :)
One of the more interesting things for fun was to poke around with a induction amplifier, you know, the "hound" in the fox and hound tone generator/ handheld probe that the phone guys use for tracing copper thru a building.
It is pretty sensitive and I've found many fun sounds by waving it around in various analog and digital equipment, it kinda gives a unique viewpoint. Used in different locations in a PC it picks up various interesting sounds that are very different according to what the system is doing, and where you are probing, memory, chipset, io/chips, cpu etc. Never found it very good for troubleshooting PC's, but lots of fun!
Also, I think the sounds you can hear around running electronics is partly caused by sympathetic viberation induced in the air molecules by high frequency energy changes happening, especially on the buses where there are long runs exposed, as well as perhaps by the caps, (?), could it be the aluminum in the caps is reacting to the energy field?, most of the round tall caps you see on a board are used on low frequency mainly power filtering applications.
I recall reading rumors of a blind fella who could play MunchMan on the TI-99/4 just by listening to the sounds in the background of the game.
While my experience is no where near that in-depth, I do remember that the computer made distinct sounds when performing certain tasks, such as reading GROM, initializing, running BASIC programs (I recall that some statements also have distinct sounds as well.)
Since then I have been able to detect certain sounds from my machines which indicate normal operations; to some extent I think we all do, just as we do with cars to "know" that something isn't right. And it's been pretty consistent through all of my computers: Commodore 64, 128D, Atari 800XL, various Amigas (amazing things heard by holding your ear to the A500 power supply,) many desktop PCs and notebooks. Even some console systems generate sounds under operation (an old NES on my shelf with a bad filter cap is good for this.)
I'm curious to know what correlations between design type, grounding, processor architecture, and other factors exist for this. Might be worth investigating like this chap did, should I find the time to do so.