December 2003 - cypherpunks-legacy

Re: crypto technique
by Karl Lui Barrus 17 Dec '03

17 Dec '03

-----BEGIN PGP SIGNED MESSAGE----- Well, I couldn't resist trying to find A, B, C, D, E, F. You may be on to something, Matt. The equations are underspecified, and have many solutions - here are some I generated (any of them match what you picked? :-) > 103 110 10 1 51 139 > 103 156 251 1 151 19 > 103 169 254 1 157 43 > 103 72 17 1 191 195 > 103 111 5 1 209 99 > 103 1 18 1 237 203 > 103 202 16 1 251 187 > 5 237 10 5 43 139 > 5 201 4 5 99 91 > 5 64 3 5 113 83 > 5 200 23 5 129 243 > 5 62 8 5 173 123 > 5 164 21 5 185 227 > 5 198 12 5 189 155 Maybe you could look at what these alternate solutions are - it could turn out that the mod operation creates extra valid solutions, which would be quite undesirable. But then, without the mod, the equation may be too easy to pick apart. Or maybe there is some other attack I haven't thought of or don't know about. -----BEGIN PGP SIGNATURE----- Version: 2.3a iQCVAgUBLMXDk4OA7OpLWtYzAQH/YwP/aTP4NwJ257A7GT1iWk7uhCYNEyJGTnkK UrEm0Pw2n1yq3bMwzEem2EPbK+XOIzP1ql0VdgpLOyQ+7quMGWl1+IKY9Ht7wd2J cy0ynJm8N1BZiJjJ2GHza+jAlqsOeVOICyT7f6Jxf/RU79/KSGQ/Jb0j52sHgrEi LfIBPXZueUc= =nzmt -----END PGP SIGNATURE-----

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Photocopying money
by I still don't know your name, stranger. 20-Oct-1993 1925 17 Dec '03

17 Dec '03

>It's true. Canon did indeed create such a chip. It's the same chip >that's used in vending machines to scan dollar bills. They built a >prototype copier which prevented copying money, but I don't know if they >actually decided to install the chip in all their assembly-line >production copiers or not tho. Nope. There is no "chip" that scans dollar bills. Dollar bill scanning is based on the magnetic ink in a few simple stripes, the presence (actually, absence) of UV fluorescent inks, and not on optical recognition per se, and besides, we all know how "reliable" such machines are. NOT! Besides, even if a pattern-match chip existed that could do it fast enough, simply turning the bill a few degrees (say, 45 degrees, across the glass) would render the problem intractable... And how about adding a background of stripes... something to really confuse the chip.... Sorry, no. -Bill

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Re: Paper Shredders
by koontzd＠lrcs.loral.com 17 Dec '03

17 Dec '03

Having been an AFSC 30670 (Electronic and Cryptographic Equipment Systems Technician), and been assigned in hazardous areas you use document destroyers on paper stuff - glass vials with grenade fuses). Equipment destroyers were 35 lb thermite charges, designed to sit on top of a standard piece of equipment in a 19 inch relay rack. I had orders to Iran but got diverted when the Shah fell. The liquid in the document destroyers was clear, and we got to set one off for demo purposes twice a year (never did get to set off thermite, though). Had a one acre room half filled with crypto, thermite would have brought the roof and lots of airconditioners down. All the key cards were treated with lead acetate, they would burn without leaving anything but a greasy wisp of ash.

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Re: crypto technique
by Karl Lui Barrus 17 Dec '03

17 Dec '03

-----BEGIN PGP SIGNED MESSAGE----- I think the modulus operation destroys uniqueness. I don't have a proof, but after working symbolically for a while, I tried an example: f = a x + b g = c f^2 + c f + d where I picked a = 11/2, b = 8, c = 25/2, d = 3. I also pick P = 16 to keep it small. So g = 903 + 4675/4 x + 3025/8 x^2 mod 16 and if I reduce each coefficient mod 16, I get g' = 7 + 3/4 x + 81/8 x^2 mod 16 Great so far. (And I checked to see that g and g' are equal). So let's look at all possible messages and their encryption: x g'(x) x g'(x) - - ----- - ----- 1 15/8 9 15/8 2 1 10 3 3 35/8 11 67/8 4 12 12 2 5 63/8 13 127/8 6 8 14 2 7 99/8 15 67/8 8 5 16 3 There is a serious problem in the above: the messages 10 and 16 encrypt to the same ciphertext; 11 and 15 also; and 12 and 14. The ciphertext 3 decodes to 10 or 16, 67/8 decodes to 11 or 15, 2 decodes to 12 or 14. That's 6 out of 16 messages, a sizeable 37.5%. This behavior may have uses in fair coin flipping or some sort of oblivious transfer (I am not claiming this in the general case, just in the example above!), but not as encryption. Besides, the fact that even messages encrypt to integers and odd messages encrypt to fractions probably isn't good. So Matt, with the numbers you used to generate the challenge problem, see if any messages encrypt to the same ciphertext, just as a check. -----BEGIN PGP SIGNATURE----- Version: 2.3a iQCVAgUBLMXPfIOA7OpLWtYzAQFoowP/XLN/poS5kB49IdCBxDe5lVUK05XZYNh+ 0vlBCjDwczqeER5SZMRPagyKSP4qbJb+BFPCNIcw0fcDrSlGCrYejzpgnn5N8vsM KmxlUE+1+8SSIsyyz6ctj7tLFp7wArxgVlOjjxQ7Yj92CIX81IShpvqWPu7rdqWN 1cCpphAwzHI= =d0rL -----END PGP SIGNATURE-----

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by Gregory W. Kamen 17 Dec '03

17 Dec '03

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Re: Paper Shredders
by owen＠autodesk.com 17 Dec '03

17 Dec '03

> Stanton McCandlish says: > > > Does anyone know of an AFFORDABLE shredder that really destroys documents > > > by cutting them into confetti, rather than the easy-to-reassemble strips > > > that the typical shredder does? > > > > Yeah, it's called fire. > Fire is, of course, an optimal solution, and those of us who live or > work in a building with a fireplace or incinerator would do well to > use it. However, its hard to spend every day burning things, and > besides that, many of us live and work in urban areas where fireplaces > and other places you can burn large numbers of papers are rare. The > question is thus not out of place. brings back ugly memorys of burn detail, back when I was stationed at a SAC command and control post up in the mountains near Westover AFB. Every scrap of paper that was discarded had to be incinerated, and we rotated through a schedule that made sure everybody got their chance to share the experience. > By the way, the standard method for destroying embassy documents in > case of siezure (not done during the Iran hostage crisis) is > reportedly Thermit grenades. (Thermit would likely reduce a filing > cabinet to slag in moments.) Sounds to me like an enterprising pyro could have a nice little operation, contracting with individuals to burn or blow up their sealed bags of trash. I understand that Beavis and Butthead might be looking for a new job, hey the little weinerheads might amount to something after all! :-) LUX ./. owen

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Re: crypto technique
by Karl Lui Barrus 17 Dec '03

17 Dec '03

-----BEGIN PGP SIGNED MESSAGE----- Another possible problem with the technique is that the multiple solutions are all valid. For example, with two nestings and a = 11/2, b = 8, c = 25/2, d = 3, P = 16 I obtain g = 903 + 4675/4 x + 3025/8 x^2 mod 16 g' = 7 + 3/4 x + 81/8 x^2 mod 16 where the g' is obtained from g by reducing the coefficients mod 16. Solving the resulting equations yields two solutions: a = 11/2, b = 8, c = 25/2, d = 3 (what I chose) a = 31/2, b = 6, c = 17/2, d = 2 Plugging in the second solution: h = 359 + 6851/4 x + 16337/8 x^2 mod 16 h' = 7 + 3/4 x + 81/8 x^2 mod 16 Notice that h' equals g'! So the other solution can be used to form the same polynomial (which we already saw doesn't encrypt uniquely). Can this other solution be used for decryption as well? I'd check but I've REALLY got to go study now :-) -----BEGIN PGP SIGNATURE----- Version: 2.3a iQCVAgUBLMXZsYOA7OpLWtYzAQFjMAP/Si1RuZjfnBNjLauB20rXaUXQMQqyiWBU n/ur7ckXSEmWnADYQqZqCy1tb/+vf5zThQD2IpbF5IH8roxYG99nZQBvvtZAQfEO 3EdbM1esMTS/I0DwcLqkuG26GNNWYGZWi8MQ/0+eXfMa9BXZvkDTuuVBzzHBSXxW 84CVKvitZ68= =FeJW -----END PGP SIGNATURE-----

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Clipper Chip report on 700 Club today (Wednesday)
by mlshew＠netcom.com 17 Dec '03

17 Dec '03

I hear there will be a report on the Clipper chip on today's (Wednesday, October 20) 700 Club. Sorry for the very late notice. (The 700 Club, for those without benifit of a handy TV schedule, will be on at 10:00 pm eastern on the Family Channel, and then at 2:00 am Thursday morning. I don't know if there are different feeds for the different time zones, so your milage might not vary.)

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Wizardry's Encryption
by Robert J Woodhead 17 Dec '03

17 Dec '03

Matthew writes (about how Wizardry was encrypted): > But, alas, the character files were in plaintext, and > numerous people figured out how to edit them. They were that way for two reasons: performance (they were always being read and written) and reality (it was a known plaintext situation, since the user could change his character in any manner of methods, like simply trading gold around between the characters, and thus map out the database) Encryption in those days wasn't intended to be strong; it was intended to be strong enough to hold off the pirates for the crucial first few months of sales. Given that we were pushing the machines to the limit of their performance envelopes, we couldn't take too much of a hit (time or code-wise) for strong encryption. And I think Sir-tech still replaces Apple II discs, but I am no longer involved in the company, so you'll have to call and ask them. ;^)

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Anon Bank Accounts / Imminent Demise of US Govt (Conclusion)
by Robert J Woodhead 17 Dec '03

17 Dec '03

Stanton McCandlish asks: > If the govt is oppressive at all, why support this? Perry E. Metzger posits: > Who needs to break it [government]? At the current rate, > it will have destroyed itself within a decade. My answer is simple: the alternative is worse. Anarchy is usually very uncomfortable, unless you have more guns and money than anyone else. Also, the current US government is, at it's core, based on sound principles. If it crashes and burns, what is it more likely to be replaced by? Whether you like it or not, you live in and are supported by a society, in a myriad of ways. The maintenance and improve- ment of that society, and the betterment of your fellow human beings, ought to be a primary goal. It is for me. And finally, Sameer Parekh opines: > I'd suggest that the politics discussion be taken to another > forum? A good suggestion. I've made my point, and perhaps infected a few people with a meme or two. Time to shut up. Best, R

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