5 ms·
How to intercept Skype calls
"Researchers have discovered trick that allows encrypted VoIP calls like Skype to be deciphered without the need to crack encryption.
The method, dubbed "Phonotactic Reconstruction", exploited the Linear Predictive Filter, a system used by Voice over Internet Protocol platforms to transmit conversations by creating data sets from spoken English.
The researchers from the University of North Carolina said while you shouldn't ditch Skype, cryptographic system that leaked as much information as they managed to get are immediately deemed insecure.
- r3demon 15y agoEven if it's possible to weaken encryption in Skype, it could be still strong enough and require a billion-dollar effort to decrypt a single conversation.
- deleted 15y ago[deleted]
- eru 15y agoHave you read the article?
- christkv 15y agoI think they are saying that they don't need to crack the encryption due to the encrypted data containing patterns that still matched phonemes. It's basically a failure in the encryption for skype that the stream is not mixed up enough to avoid fixed patterns. Makes you wonder how long they have been decoding skype messages for intelligence reasons.
- FlowerPower 15y agoForever. When your moneysack is bottomless you can do anything, no need to decrypt it, man-in-the-middle it, if that cant do, switch the victims CPU for your own "special" one. Intelligence organizations have been breaking silently into peoples homes for hundreds of years, its a skill well developed. To then change a chip on your computer, is peanuts.
- bad_user 15y agoGeez, do you also wear a tinfoil hat, or was this humor?
- deleted 15y ago[deleted]
- dnadolny 15y agoHumor? The NSA tried to introduce an encryption chip[1] and get telecommunications providers to use it. It had a backdoor so that they could decrypt anything that used it. I vaguely remember hearing other stories where chips were made with secret backdoors in them, but I can't seem to find any. [1]: http://en.wikipedia.org/wiki/Clipper_chip http://en.wikipedia.org/wiki/Clipper_chip
- neworbit 15y agoI have the strangest feeling I'm probably feeding the troll, but... Why would you bother with CPU switching and such when you could just install an old fashioned microphone? If you were actually inclined to eavesdrop, it seems like hardware-subverting your PC is a lot more expensive and fragile than software or a specialty purpose bug elsewhere in the room.
- eru 15y agoA pretty clever attack. I wonder what the Skype people will do about it. (It seems like any algorithm that has e.g. a variable transmission rate will be relatively easy to attack.)
- by 15y agoIt's called traffic analysis https://secure.wikimedia.org/wikipedia/en/wiki/Traffic_analysis https://secure.wikimedia.org/wikipedia/en/wiki/Traffic_analy...
- tomp 15y ago> It seems like any algorithm that has e.g. a variable transmission rate will be relatively easy to attack. Not really, just make the variability of bandwidth not depend on the amount of data that's being transmitted... i.e., add a stochastic factor to it (random). If there's enough noise, you probably shouldn't be able to decipher the words spoken.
- JoachimSchipper 15y agoPeople seem to be misinterpreting the article, so here's a technical explanation: - Skype's encryption algorithm is not, itself, broken; - Skype uses a "prediction" algorithm to compress voice streams; - therefore, words have a specific pattern of bandwidth use (toy example: "techcrunch" spikes around the "-crunch", since you'd expect "-nology"); - bandwidth use of encrypted compressed data is equal to bandwidth use of data that has only been compressed; - these patterns (which can be detected "through" the encryption) allow fairly good reconstruction of the voice stream. If you like this kind of thing, Google "ssh keystroke timing attacks", or, more generally, "traffic analysis".
- caf 15y agoThe Linear Predictive Coding used for compressing speech does it at a much lower level than "technology" versus "techcrunch" - it uses a physical model of the human vocal tract (I've actually implemented the LPC used in the GSM codec).
- JoachimSchipper 15y agoYes, I was intentionally simplifying it to only what was essential to this article. Do you have a better one-sentence explanation?
- caf 15y agoI think it's clear enough without the example in the brackets. Anyway, it wasn't really a criticism, just more detailed information that I thought readers might appreciate.
- lgeek 15y agoI think your explanation is misleading. LPCs predict the shape of the speech waveform, nothing higher level than that.
- JabavuAdams 15y ago> Skype's encryption algorithm is not, itself, broken Skype's encryption has not been cracked, but it is broken in the sense that it preserves exploitable structure in the ciphertext. The ciphertext should be essentially random, shouldn't it?
- sc00ter 15y agoOriginal research paper: http://www.cs.unc.edu/~amw/resources/hooktonfoniks.pdf http://www.cs.unc.edu/~amw/resources/hooktonfoniks.pdf It's a facinitating piece of research, and a great collaberation between the CompSci and Linguistics depts of this University. The title above is linkbait, as the paper is about analysing any variable bitrate audio stream. Mobile phones and enterprise VOIP solutions could be just as vulnerable. ]
- pnathan 15y agoIt appears that a defense against this approach is to use a stream cipher with constant blocklengths. Does that sound like a reasonable interpretation of the paper?
- joshaidan 15y agoDoes anyone know if voice traffic actually passes through super-nodes, or are super-nodes just used for authentication, and punching holes through NAT? If it does, can you point to a reference stating this? Anyway, billions of people have unencrypted conversations through this telecommunications system called the plain old telephone service. At least Skype is one step better.
- bdhe 15y agoDoes anyone know if voice traffic actually passes through super-nodes, or are super-nodes just used for authentication, and punching holes through NAT? If it does, can you point to a reference stating this? Yes, Skype traffic does pass through supernodes. I know people working on using Skype to route around censorship and supernodes allow you to connect two clients even if the direct connection between them is dropped. Here's an article in Skype about rate limiting if you're running as a super node which is further evidence that voice traffic does pass through super-nodes. http://forum.skype.com/index.php?showtopic=13780 http://forum.skype.com/index.php?showtopic=13780
- spoiledtechie 15y agoIts pretty intense research and one that is highly valued in the DoD world. They pay top dollar for this type of research and most likely did. If I remember correctly, they put out a call about 1 year ago for this type of "breaking" to be done on Skype. Mainly to listen to calls between suspects...
- mirkules 15y agoUsing pattern recognition to guess words based on occurrence frequency is not a new concept, but the way they applied it is awesome. I saw something similar in Defcon 17 where the researchers recorded sound from a keyboard (using lasers as microphones, but that's irrelevant), then analyzed breaks in typing to attempt to guess what the victim was typing. Fascinating stuff!
- Splines 15y agoSo... I need to make Skype calls with the water faucet and/or some music playing now?