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| Sci.crypt Can Not Break Cryptosms; after long time nobody cracks cryptosms | |
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| Topic Started: Aug 29 2005, 08:56 PM (392 Views) | |
| Donald | Sep 1 2005, 12:25 PM Post #16 |
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Unregistered
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That depends on what kind of Cryptography!  Modern Crypto, you wouldn't even attempt by hand, it's machine work. But before you even considered that, you should try playing with pen and pencil ciphers. "Alvin's Secret Code" by Clifford Hicks is a great start there, (It's a kid's story, but a good one). But there are DOZENS of books available out there that can give you a kick start on decrypting pen and paper ciphers. From there, you can move on to the serious stuff, IF you have the math for it. I don't. 
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| Theophrastus Philipus Aureolus B | Sep 1 2005, 01:27 PM Post #17 |
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Giving the source code public is a big decision, since the makers of the program lose all their rights when they do. It is surprising that so many programs are opened source. How can people afford to spend so much time for little or no return? == "The dose makes the poison." - Paracelsus  |
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| PulsarSL | Sep 2 2005, 03:31 PM Post #18 |
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Super member
  ![]](http://209.85.122.85/static/1/pip_r.png)
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I've often wondered that (especially for things like PHPBB, which IMO could be sold). I suppose their return is getting their name in the credits... and I think they also like the challenge. |
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| Donald | Sep 2 2005, 04:10 PM Post #19 |
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Unregistered
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Releasing the source does not necessarily mean a product is free. PGP releases thier source, but they charge an arm and a leg for the product. It's a GOOD product mind you, well worth it, but they ARE making money. |
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| PulsarSL | Sep 3 2005, 02:22 AM Post #20 |
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True... but PGP actually has infrastructure to maintain |
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| insecure | Sep 9 2005, 10:29 PM Post #21 |
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Taking those questions in reverse order: It's not illegal to discuss general principles of cryptography and cryptanalysis. If you are in the USA, because of the Digital Millennium Copyright Act you don't have free speech, so you have to be very careful when discussing reverse engineering. Consult a lawyer if need be. Yes, there is software to help you crack encrypted messages, but the more it does for you, the less it teaches you - unless you write it yourself (which is much more fun anyway). Cracking stuff by hand is a lot of fun, but not terribly effective against sophisticated ciphers. Alan Turing's Enigma-cracking bunch achieved wonderful things "by hand" in terms of analysis, but they still needed to test a huge number of potential keys - so they invented the stored-program digital computer. (This fact was classified for so long that the Americans genuinely thought, and still think, that they invented it!) But cracking by hand is still the best way to start. Consider this simple cipher, known as the Caesar cipher (a special case of a class of ciphers called "shift ciphers"). Can you crack it? By hand? FDQBR XFUDF NWKLV Hint: think "shift cipher". This looks impossible, but it's actually quite simple. Julius Caesar used it. Please note that I've used a longstanding convention of dividing the ciphertext into groups of five cipher characters. The spaces of the original message have been removed, so after decoding one has to mentally reinsert them. Once you've cracked a shift cipher, I trust it will whet your appetite a little. The next challenge would be a monoalphabetic substitution cipher - and that's where your education really starts. |
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| PulsarSL | Sep 10 2005, 06:22 PM Post #22 |
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Alright... I figured either D or F was equal to E because they are the most frequent, so I tried both, but came up with nothing. Would you have to try 26 different levels of shift to crack it? |
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| Revelation | Sep 10 2005, 08:50 PM Post #23 |
Administrator
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Alright, that was easy. You should write another application for this one PulsarSL. It is just a shift by three (same as Ceasar's).
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RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN | |
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| Donald | Sep 11 2005, 04:01 AM Post #24 |
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On a message this short, you can't trust frequency analysis. Just not enough letters. For example, look at the frequencies of this short example: A BOX OF XYLOPHONE'S. O=4 X=2 A,B,E,F,H,L,N,P,S,Y=1 And it doesn't even have to be that odd of a sentence. I DON'T CLIMB MOUNTAINS. I=3 N=3 M=2 O=2 T=2 A,B,C,D,L,S,U=1 So even if the message sender isn't attempting to manipulate the frequencies, you just can't trust that they have much meaning at all in very very short message. By the way, The ACA (American Cryptography Association) has a "Crypto Drop Box" that is full of interesting resources: http://www.und.nodak.edu/org/crypto/crypto/resources.html One of which is a Classical Cryptography course by Randy Nichols (LANAKI) President of the American Cryptogram Association from 1994-1996. You can find his course here: http://www.und.nodak.edu/org/crypto/crypto...ki.crypt.class/ You can find the first 12 lessons of the same course in a very nice HTML format on Joe Peschel's page: http://members.aol.com/jpeschel/lessons.htm If you are interested in learning classical cryptography, you might find these lessons helpful. I'd also consider purchasing Helen Fouche Gaines book "Cryptanalysis, a study of ciphers and their solution". It's not real user friendly, but it's full of good information. It's available new at Dover And, one of my favorites, "Alvin's Secret Code" by Clifford B. Hicks. You can still get it used at Amazon Ok, yeah, it's a kids book, but I STILL enjoy it, AND it's an excellent course in begining cryptography. For the definitive history of cryptography, you want: David Kahn's "The Code Breakers" And for a lighter, (and cheaper), but still very good history and introduction to cryptography, try: Simon Singh's "The Code Book" Donald |
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| insecure | Sep 11 2005, 04:28 AM Post #25 |
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Elite member
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On the subject of kids' books, I agree entirely with Donald that they can be very useful for broaching a subject that you either have never studied or have not studied for some time. You should take them with a pinch of salt (sometimes, for forgiveable reasons, they over-simplify), but they can be handy nonetheless. I bought a mathematics textbook long after leaving school, because I realised that my mathematical ability was not all that it should be. The textbook was aimed at 15-18 years, but I found it extremely useful despite having exceeded that age range for - er - quite a while! Kahn: I don't have a copy, but it has an excellent reputation within the cryptographic community. Singh: This does not have an excellent reputation, but don't let that put you off. It's a very good book, in my opinion. Just think of it as a kid's book for grown-up kids. That is, let it give you the basic idea, but don't assume that everything you read in there is correct. To Donald's excellent list I would add: "Applied Cryptography", 2nd edition, by Bruce Schneier. "Handbook of Applied Cryptography" (not by Schneier, the closeness in titles probably being coincidental), available online, legally, for free. You shouldn't have any trouble finding it. Donald E Knuth's currently-three-volume work "The Art of Computer Programming" is a useful resource for some aspects of cryptography. For example, it gives you stuff like bignum algorithms, Miller-Rabin, and (I think) RSA. Knuth seems recondite at first, but I actually found his description of Miller-Rabin superior to that of Schneier. (I thought: "Knuth? No way. Schneier? Yeah." I looked in Schneier. I thought: "Er, WHAT?" I thought: "Knuth? Maybe." I looked in Knuth. I thought: "Ohhhhhh! That's how it works." You get the picture.) The sci.crypt FAQ is also well worth a read. It may help to explain why ciphertext-only challenges are generally not considered to be worth the Web space they take up (except as puzzles, for entertainment or educational purposes). |
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4:45 AM Nov 27
