I heard something interesting which made me think. (gasp) I heard that if you encrypt a file with the xor encryption alg. multiple times with different keys, you get an encrypted file with a coorisponding effective key which has some interesting properties. The key in such a system would have a length equal to the Least Common Multiple of the lengths of the original key. So, if you used keys of length 1,2,3,5,7,11,13, you would have an effective key-length of 30,030 bytes! Of course, you could use more than one 5-byte key if you wanted, and some of the bytes should be greater than 127. Not knowing any better, it occurs to me that given a 30,030 byte key, and the task of finding the original keys that make it up, (if any) I'd be out of luck. It would seem that "factoring" this large key into smaller keys would be a tough job...perhapse almost as hard as the factoring problem in a finite group? Brute-force and known plaintext attacks are possible, but lets forget that for (just) a moment. If someone DID find the required 30,030 bytes required to read your massage, you could just as easily show them another 30,030 bytes which would decode the message into the U.S. Bill of Rights if you wanted to. You could keep such One Time Pads laying around your hard disk if you wanted to...in zip format, perhapse. You would always be able to get the true plaintext by simply knowing the 7 key-words. But few others would be so lucky. The point being that there would be some degree of plausible deniability with such a cypher. For the sake of arguement, lets say that the plaintext was first encrypted with some strong crypto. Then we used the xor crypto with 7 keys. It would be pretty hard to see what had been done. Now we deal with the brute force attack to get the original keys. Lets say that someone does get 7 words which will decrypt your ciphertext into a plot to distribute <your favorite scum> to <your favorite victim>? If you had to, I'm sure you could reverse engineer a completely different set of keys which will form the same plaintext. If you absolutely had to, you might be able to come up with 7 words which will decrypt your ciphertext back into the Bill of Rights, thus giving you absolute plausible deniability. As far as known plaintext attacks go...well, we hope that doesn't happen. ;^) Well, I'm about to wrap this up. Some time ago, I proposed hiding messages on the end of other files such as executable. Well, if we pgp encrypted a file, then xor encrypted the result with 7 keys and stuck that on the end of 4dos.com, which is over 64K BTW, I find it hard to believe that you would be caught readily. I haven't had time to investigate the harmonic qualities of such a cypher, but it seems feasible. You could delete and wipe the encryption program from your harddisk. (after uploading the source/executable to your local bbs) There would be tough times for anyone who had to pin a given message on you. Well, what do you think? I hope to drum up as much discussion here as with the "radical paranoia" thread, from which I learned a lot. Well, I promised to wrap this up, so I guess I'm done. +-----------------------+-----------------------------+---------+ | J. Michael Diehl ;-) | I thought I was wrong once. | PGP KEY | | mdiehl@triton.unm.edu | But, I was mistaken. |available| | mike.diehl@fido.org | | Ask Me! | | (505) 299-2282 +-----------------------------+---------+ | | +------"I'm just looking for the opportunity to be -------------+ | Politically Incorrect!" <Me> | +-----If codes are outlawed, only criminals wil have codes.-----+ +----Is Big Brother in your phone? If you don't know, ask me---+
J. Michael Diehl <mdiehl@triton.unm.edu> says:
I heard something interesting which made me think. (gasp)
I heard that if you encrypt a file with the xor encryption alg. multiple times with different keys, you get an encrypted file with a coorisponding effective key which has some interesting properties. The key in such a system would have a length equal to the Least Common Multiple of the lengths of the original key.
Sadly, the Friedmans already cracked the "multiple repeating xored keys" cypher a while back -- about fifty years ago. Don't be embarassed, by the way -- everyone comes up with cyphers that have been cracked before. However, I would suggest reading "The Codebreakers" and the current literature before proposing new systems. Perry
According to Perry E. Metzger:
Sadly, the Friedmans already cracked the "multiple repeating xored keys" cypher a while back -- about fifty years ago.
I knew it was crackable. That wasn't the point. The point was data hiding.
Don't be embarassed, by the way -- everyone comes up with cyphers that have been cracked before. However, I would suggest reading "The Codebreakers" and the current literature before proposing new systems.
I'm not embarassed; I didn't develope the crypto I was discussing. I was simply discussing a new application for it. I will read Codebreakers. Thanx. +-----------------------+-----------------------------+---------+ | J. Michael Diehl ;-) | I thought I was wrong once. | PGP KEY | | mdiehl@triton.unm.edu | But, I was mistaken. |available| | mike.diehl@fido.org | | Ask Me! | | (505) 299-2282 +-----------------------------+---------+ | | +------"I'm just looking for the opportunity to be -------------+ | Politically Incorrect!" <Me> | +-----If codes are outlawed, only criminals wil have codes.-----+ +----Is Big Brother in your phone? If you don't know, ask me---+
What you are talking about sounds like the original Vernam cipher that Dave Kahn talks about in _CodeBreakers_. There, he was using a teletype with two XORing tapes. One tape was 1000 characters long, the other was 999. Thus, 999000 characters would have to go past before the system repeated. HOWEVER, once it does repeat, all security is compromized. Even before that time, I believe there are subtle attacks you can use based on the repetition of the keys. So, this is not a secure cipher method. I would personally suggest tacking an 128 bit IDEA key onto 4dos.com instead. Or use DES even. BTW: Though you could come up with a 30Kb+ string which when XORed would give you any plaintext, you could not come up with a few small strings which when used over each other would give you that. There just isn't enough information to make that possible. -- PGP 2.3 Key by finger
According to Douglas Sinclair:
What you are talking about sounds like the original Vernam cipher that Dave Kahn talks about in _CodeBreakers_. There, he was using a teletype with two XORing tapes. One tape was 1000 characters long, the other was 999. Thus, 999000 characters would have to go past before the system repeated. HOWEVER, once it does repeat, all security is compromized. Even before that time, I believe there are subtle attacks you can use based on the repetition of the keys. So, this is not a secure cipher method. I would personally suggest tacking an 128 bit IDEA key onto 4dos.com instead. Or use DES even.
The point wasn't to be unbreakably secure; it was to be UNFINDABLY secure. We convolute an allready encrypted message to the point of not being recognizable as cyphertext, then we hide it on the end of a file. We want it to look like garbage.
BTW: Though you could come up with a 30Kb+ string which when XORed would give you any plaintext, you could not come up with a few small strings which when used over each other would give you that. There just isn't enough information to make that possible.
Agreed. This leaves us with several OTP's laying around in zip format. This isn't so bad as long as we don't forget the original 7 keys. The main purpose of all of this is plausible deniability. Thanx for your comments. Still listening. +-----------------------+-----------------------------+---------+ | J. Michael Diehl ;-) | I thought I was wrong once. | PGP KEY | | mdiehl@triton.unm.edu | But, I was mistaken. |available| | mike.diehl@fido.org | | Ask Me! | | (505) 299-2282 +-----------------------------+---------+ | | +------"I'm just looking for the opportunity to be -------------+ | Politically Incorrect!" <Me> | +-----If codes are outlawed, only criminals wil have codes.-----+ +----Is Big Brother in your phone? If you don't know, ask me---+
J. Michael Diehl <mdiehl@triton.unm.edu> says:
According to Douglas Sinclair:
The point wasn't to be unbreakably secure; it was to be UNFINDABLY secure. We convolute an allready encrypted message to the point of not being recognizable as cyphertext, then we hide it on the end of a file. We want it to look like garbage.
Cyphertext from any decent system ALREADY looks random. Whats the point of doing more to it? Perry
According to Perry E. Metzger:
J. Michael Diehl <mdiehl@triton.unm.edu> says:
According to Douglas Sinclair: The point wasn't to be unbreakably secure; it was to be UNFINDABLY secure. We convolute an allready encrypted message to the point of not being recognizable as cyphertext, then we hide it on the end of a file. We want it to look like garbage.
Cyphertext from any decent system ALREADY looks random. Whats the point of doing more to it?
Many encryption tools such as ripem, pgp, and dolphin can recognize their own output...which indicates that there is a footprint to that particular implimentation. +-----------------------+-----------------------------+---------+ | J. Michael Diehl ;-) | I thought I was wrong once. | PGP KEY | | mdiehl@triton.unm.edu | But, I was mistaken. |available| | mike.diehl@fido.org | | Ask Me! | | (505) 299-2282 +-----------------------------+---------+ | | +------"I'm just looking for the opportunity to be -------------+ | Politically Incorrect!" <Me> | +-----If codes are outlawed, only criminals wil have codes.-----+ +----Is Big Brother in your phone? If you don't know, ask me---+
J. Michael Diehl <mdiehl@triton.unm.edu> writes:
Many encryption tools such as ripem, pgp, and dolphin can recognize their own output...which indicates that there is a footprint to that particular implimentation.
in this case, you're just trying to garble what people see so why not just xor "hello, world." /bin/csh or \command.com on top of it to avhieve that result. No need for anything significant, I mean, if you xor 'X' over the whole thing, you've achieved the same result - after all, if someone wants to xor 'X' to knock that level of encryption(if I may call simple substitution "encryption") then it's fair to assume that the person knows it's cyphertext and they want the information below it, so that's a good place to use some decent encryption.. "congratulations, you have found the secret message. send the answer to old pink care of the funny farm" (Pink Floyd, The Wall (backmasking)) is what readily comes to mind when i see what you're getting at.. after all, searching a disk for data that fits specific patterns is one thing, figuring out that one of the index files for a database program with literally hundreds of database files and indecies (I used to work on programming such a database, so I know they exist and that they are a perfect hiding place for just about everything) is actually an encrypted file isn't a walk in the park. anyway, enough babbling - hope some of it makes sense. =) the park -- Mike Sherwood internet: mike@EGFABT.ORG uucp: ...!sgiblab!egfabt!mike
J. Michael Diehl <mdiehl@triton.unm.edu> says:
According to Perry E. Metzger:
J. Michael Diehl <mdiehl@triton.unm.edu> says:
According to Douglas Sinclair: The point wasn't to be unbreakably secure; it was to be UNFINDABLY secure. We convolute an allready encrypted message to the point of not being recognizable as cyphertext, then we hide it on the end of a file. We want it to look like garbage.
Cyphertext from any decent system ALREADY looks random. Whats the point of doing more to it?
Many encryption tools such as ripem, pgp, and dolphin can recognize their own output...which indicates that there is a footprint to that particular implimentation.
Intentionally. They INTENTIONALLY put magic numbers at the head of the file. If you remove that, the file is random. You can hack PGP not to use headers if you really want to. Proposing some useless cryptosystem just to hide the headers is completely unneeded. Perry
participants (4)
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Douglas Sinclair -
J. Michael Diehl -
mike＠EGFABT.ORG -
Perry E. Metzger