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Codebreaking - Taking the First Step?
Master Spy asks: "Here's something that the Slashdot community might be able to help with. If you receive a message in code how do you take the first step? Back in the days of WWII it was easier. The codebreakers at Bletchley Park already knew that the messages were encoded using an Enigma machine so all they had to do was work out the positions of the rotors using brain power, the Bombe or later the Colossus machine. American codebreakers also knew the basic details about the methods the Japanese used but now however things are more complicated. Suppose you are listening to a transmission and you receive the following: 'sdjek dYqkP 1Nt$% GGl9) MHrYD +++' How do you know how the message has been encrypted? It could be an Enigma machine, it could have been XOR'd with a second message or a one-time pad or it could use some form of software encryption such as Blowfish or DES. Before you start ripping the message apart for decoding how do codebreakers find out what method has been used to encode the message?"
The only, only thing you can expect to learn is who's communicating with whom [and when / how much information is exchanged] ( you probably know this already ) , and what protocol they're using ( it's probably unbreakable ).
Chances are, if you are intercepting an encrypted stream, you are intercepting an unbreakably encrypted stream.
Perhaps you are thinking that if only you knew what protocol the stream is using, you might look online and see if that protocol has been cracked.
Don't waste your time.
The chances are approximately 0 that the stream you are intercepting is using a protocol that has been cracked, or that it is using a keyspace you can brute-force for under a few hundred thousand dollars, or in under a matter of years.
Sorry -- you have a higher chance (almost infinitely higher -- as I said, the chance you will succeed in what you are asking to do is approximately 0) of port-scanning the machine at the source or the destination and 0wning it than you do of breaking the stream.
I don't say this to mean you should give up -- just that you're phrasing your question wrong. Don't discount the 0wning venue of attack.
For every million desktop machines communicating over TCP/IP, only a matter of a few dozen will have 0 exploitable security weaknesses. (However, most security weaknesses are unknown.)
Find out what kind of machine is at the source and the destination, then 0wn one of them. Chances are almost overwhleming that it's possible, if not with a remote exploit, then through social engineering. (Send an attachment that will be opened on either end of the communication, or induce either end to visit a web page in a browser that is exploitable (=, basically, every browser except Lynx).
If they browse with Netscape or Internet Explorer, chances are almost overwhelming that they can be owned.
It's not that hard to get someone to browse to a certain page, if you know anything at all about who that person is.
Back to your original question: gone are the days that protocols were breakable by any hotshot think tank. Today only implementations are, and rarely at the level you're trying to address. Don't break the code -- break into the system.
Hope this helps.