Re: encrypted email software
DES isnt secure? And where was it that you got this precious little piece of information?
You mean to tell me you believe what your government tells you about DES? Come on now! It's been public knowledge for quite some time that the NSA has a backdoor to DES and the FBI and other agencys know it.
Its public knowledge? were's the proof? Not one academic researcher has found it (and lived to publish about it). On the other hand some very respectable cryptographers have been able to show that the design critereon has made for very well chosen parameters. The FBI has shown that they dont know a backdoor in DES or at least they wont use it against suspects. There have been cases were data was encrypted with DES and the suspect refused to turn over the keys.
I certainly hope you were kidding!
-- Bob Tannen Borland International 1800 Greenhills Rd. Scotts Valley, CA. 95066
rtannen@borland.com RTANNEN @ BORLAND (MHS)
Timothy Newsham says:
DES isnt secure? And where was it that you got this precious little piece of information?
You mean to tell me you believe what your government tells you about DES? Come on now! It's been public knowledge for quite some time that the NSA has a backdoor to DES and the FBI and other agencys know it.
Its public knowledge? were's the proof? Not one academic researcher has found it (and lived to publish about it).
100% correct. Although DES is likely breakable by brute force, that can only be done at tremendous expense. The back door notion, although still possible, is now not believed to be true. Perry
The FBI has shown that they dont know a backdoor in DES or at least they wont use it against suspects.
For what it is worth, an FBI agent here in Boston once told me a story (over lunch) about a drug case involving a seized PC with DES encrypted files. The FBI folks called up "some friends" at NSA, who were able to decrypt the files. They couldn't use the info in court (since that would reveal what the NSA could do), but the information was valuable to them nonetheless. Now, I don't know whether to believe this or not. There was at least one interesting detail/inconsistency in the story (he mentioned that when they got the PC back from NSA they were somehow able to tell by examining some file-modification times that the decrypt had taken 12 minutes. It's not immediately obvious to me why this would be so.) The guy who told me the story isn't particularly technical; neither is he totally non-technical (at one point he told another story about how difficult it is to explain hexadecimal to a jury.) I don't think he would be above a little desinformatsiya. I don't see what he would gain from it, other than appearing to be more technical/powerful/in-the-know than he really is. That NSA can break DES is widely suspected, even if unproved. Cheers, - nick P.s. The truly funny postscript to this story is that halfway through the aforementioned lunch with this FBI fellow, I looked down and realized I was wearing one of the hack LOD T-Shirts. After I finished choking on my biriyani, he wanted to know where *he* could get one ...
"Perry E. Metzger"
100% correct. Although DES is likely breakable by brute force, that can only be done at tremendous expense. The back door notion, although still possible, is now not believed to be true.
People first thought there was a back door because they wouldn't release enough info on the algorithm to give people a chance to see if they trusted it or not. After it was all common knowledge, people examined it and came to the conclusion that it was secure, though questions are still around about why it was changed from 64 bit to 56 bit, which is also why it is believed that the NSA has computers that can break it by brute force in a reasonable amount of time, but nevertheless it is a brute force attack. That's how I've heard (from various sources) the whole story with DES goes, and it seems like a reasonable one. -- Mike Sherwood internet: mike@EGFABT.ORG uucp: ...!sgiblab!egfabt!mike
it and came to the conclusion that it was secure, though questions are still around about why it was changed from 64 bit to 56 bit, ... Didn't someone figure out a way that the 64 bit version would be more vulnerable to differential cryptanalysis (which was known to IBM as the "sliding attack" back when DES was being developed) than
the 56 bit one was? And I've heard indications that the predecessor
"Lucifer" at 128 bits had some trivial "meet-in-the-middle" attack
that left it at least as weak as 64 bits.
The only "backdoor" concept I've heard which had a technical
basis behind it was a few years back, when some researcher figured out
a way to *produce* S-boxes with particular types of holes, and
concluded that it was impossible to identify if the holes where there
or not unless you knew the precise formulation... I think it even had
a two-of-three challenge, ie, published 3 sets of s-boxes, one or two
of which were "trapped" in this way, as a challenge for people to find
methods of locating them. (The technical basis stops there -- the
psychological or political question that follows is "did NSA/IBM know
about this technique? Assuming they did, did they choose the s-boxes
with or without holes?")
_Mark_
People first thought there was a back door because they wouldn't release enough info on the algorithm to give people a chance to see if they trusted it or not.
not the algorithm, which was public from the start, but the rationale behind the selection of its parameters.
After it was all common knowledge, people examined it and came to the conclusion that it was secure,
the rationale remains classified; some people question nsa's motivation in keeping that aspect of des secret. i believe nsa keeps it secret to avoid teaching potential (or imaginary) adversaries advanced cryptographic techniques. (and also because keeping secrets is what nsa is all about. they seem to be very, very good at it.)
though questions are still around about why it was changed from 64 bit to 56 bit,
you mean 112 -> 56. this has been resolved -- it seems that longer keys don't impose any additional complexity on des attacks. although these attacks were discovered by the open crypto community only a few years ago, nsa had these techniques in hand long before. the bottom line is that additional key bits would not make des more secure. double des or triple des do.
which is also why it is believed that the NSA has computers that can break it by brute force in a reasonable amount of time, but nevertheless it is a brute force attack.
it has long been believed that a dedicated des-cracker is within the budget of extremely well financed organizations.
That's how I've heard (from various sources) the whole story with DES goes, and it seems like a reasonable one.
your story is pretty close to the spin i'm familiar with. peter
According to Mark Eichin:
The only "backdoor" concept I've heard which had a technical basis behind it was a few years back, when some researcher figured out a way to *produce* S-boxes with particular types of holes, and concluded that it was impossible to identify if the holes where there or not unless you knew the precise formulation... I think it even had a two-of-three challenge, ie, published 3 sets of s-boxes, one or two of which were "trapped" in this way, as a challenge for people to find methods of locating them. (The technical basis stops there -- the psychological or political question that follows is "did NSA/IBM know about this technique? Assuming they did, did they choose the s-boxes with or without holes?")
Could someone tell me what an s-box is? Thanx in advance. +-----------------------+-----------------------------+---------+ | 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---+
Could someone tell me what an s-box is? Thanx in advance.
The Data Encryption Standard (any many other crypto systems devised since) use a process of substitutions (replacing one block of bits with another) and permutations (re-arranging the bits). This process is iterated a number of times and the key is mixed in at different points. This R This L | | v | [E Expansion] | | | \ | XOR <------------- key for this round (subkey) | | | ----------------------------------- | | | | | | | | | | v v v v v v v v | ========================================= | | S1 | S2 | S3 | S4 | S5 | S6 | S7 | S8 | | ========================================= | | | | | | | | | | ----------------------------------- / | / [P Permutation] / | / \____________________________________/__ | / \ v / \ XOR <----------- | v v Next R Next L This is the basic structure of DES (if I didnt make a mistake, this is from memory). Anyway the basic idea is you take half the key (called L and R for Left and Right, but hey, I'm lysdexic). You put it through an expansion, this just mixes up the order of the bits and duplicates a few of them. Then you XOR it with the sub-key (the Key Generator is not shown). Then you split it up into 8 6-bit chunks and do a table lookup in the S-boxes, each Sbox has 6 inputs and 4 outputs. Then you re-arrange the bits in the P permutation. Finally you XOR that value with the L to get next R, and put the pre-XOR'ed value into the next L. This is 1 iteration and is done 16 times in DES, and 16*25 times in crypt(3). Crypt(3) also has the salt values which cause the swapping of two bits in the E expansion for every salt bit that is set. Before pulling apart the 64 bit input into 2 32 bit halfs (L and R) the data is passed through an Initial Permutation (IP), and at the end of the whole thing passed through (IP^-1) its inverse (this permutation isnt cryptographically that significant). The subkeys are generated by taking the input 56 bits of key, mixing them up and then successively rotating those bits, and passing them through a permutation. It outputs 48 bits of key each iteration to match the 48 bits after the E expansion. I hope I didnt make too many mistakes in the above discussion, but you get the general idea.
+-----------------------+-----------------------------+---------+ | 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---+
peter honeyman says:
still around about why it was changed from 64 bit to 56 bit, you mean 112 -> 56. this has been resolved -- it seems that longer keys don't impose any additional complexity on des attacks. although these attacks were discovered by the open crypto community only a few years ago, nsa had these techniques in hand long before. the bottom line is that additional key bits would not make des more secure. double des or triple des do.
Well, first - I believe DES was designed with 64 bit keys in mind, and then due to some technical (unspecified :-) reasons he key was shortened to 56 bits (and 56-bit version was submitted to NBS). While longer key indeed offers little protection against attacks like differential cryptanalysis - it's hard to argue that it can blow brute-force attack out of the water... And I'd be somewhat more concerned about an adversary cracking my DES-encrypted mail via brute force, than tapping my channel and collecting 2^45 of plaintext-ciphertext pairs to deduce my DES [randomly selected] key (:-). N'est pas?
it has long been believed that a dedicated des-cracker is within the budget of extremely well financed organizations.
Well, of course a government (any government :-) could build such a thing... After all, don't they get all those tax money? (:-) -- Regards, Uri uri@watson.ibm.com scifi!angmar!uri N2RIU ----------- <Disclamer>
Well, first - I believe DES was designed with 64 bit keys in mind, and then they apparently discovered it to be sensitive to the "sliding attack", ie. differential cryptanalysis...
While longer key indeed offers little protection against attacks like differential cryptanalysis - it's hard to argue that it can blow brute-force attack out of the water... But isn't the idea differential cryptanalysis *can* blow brute-force out of the water if the algorithm is sensitive to it, and the symmetries that could be introduced by 64-bit DES keying might have made it thus sensitive. It isn't just that extra key "offers little protection", it might actually *weaken* the algorithm. (No, I'm not an expert on DES, but I've followed the net, read the FIPS, read Biham-Shamir, and thought about it a bit for myself.) _Mark_
Mark Eichin says:
While longer key indeed offers little protection against attacks like differential cryptanalysis - it's hard to argue that it can blow brute-force attack out of the water... But isn't the idea differential cryptanalysis *can* blow brute-force out of the water if the algorithm is sensitive to it, and the symmetries that could be introduced by 64-bit DES keying might have made it thus sensitive. It isn't just that extra key "offers little protection", it might actually *weaken* the algorithm. (No, I'm not an expert on DES, but I've followed the net, read the FIPS, read Biham-Shamir, and thought about it a bit for myself.)
Well, to the best of my knowledge, "sliding attack" does NOT care about the length of a key - because it deduces the subkeys DIRECTLY. This means - one doesn't WEAKEN an algorithm by increasing the key length, it just doesn't help against "sliding attack"... And in order to pull out this "sliding attack" one HAS to have either enough of PLAINTEXT-CIPHERTEXT pairs, or even better - to be able to run CHOSEN-PLAINTEXT attack. How much are you afraid of such an attack against your e-mail? [Assuming you use one-time RSA-encrypted DES key, of course :-] -- Regards, Uri uri@watson.ibm.com scifi!angmar!uri N2RIU ----------- <Disclamer>
From cypherpunks-request Sun Jul 11 20:17:07 1993
participants (8)
-
eichin＠cygnus.com -
J. Michael Diehl -
mike＠EGFABT.ORG -
Nick Papadakis -
Perry E. Metzger -
peter honeyman -
Timothy Newsham -
uri＠watson.ibm.com