HDTenEightyP/NetNews huggingface dataset:
From: endacott@kuhub.cc.ukans.edu
Newsgroups: sci.materials
Subject: Building Demolition Technology??
Date: 21 Jul 92 22:52:55 CDT
Organization: University of Kansas Academic Computing Services

Our Director of Support Services poses an interesting question.  I
would appreciate any information related to improved technology for
building demolition or leads to any research in process dedicated to
this subject. I will summarize any direct mail back to the list.

If we can disolve gall stones in a quiet fashion, without destroying
"neighboring" tissue, perhaps we could disolve concrete/mortar/steel
with this same or similar technology and just "flush unwanted
buildings right down the drain!"  No fuss, muss, or noise pollution!!

Any related information will be appreciated. . . . Phil---

------- Forwarded Message Follows -------

To:         PHIL
From:       CO/RO
Date:       16 Jul 92 09:38:14 GMT+O700

Phil, I would like you to send out an inquiry soliciting input from
other institutions regarding the availability of alternative
demolition procedures to the mess causing jackhammer, air compressor
and concrete saw. As you so well know, the renovation projects on the
campuses are numerous and will continue to grow in numbers with
changes in our research and instructional programs.  The combination
of dust, noise and worker protection associated with current
demolition methods is very disruptive and annoying to "neighbors" to
the project.

    How are other institutions handling this dilemma? Are other
procedures such as ultra high pressure water being sucessfully used?

-------END OF FORWARDED MESSAGE--------
From: snyder@henry.ece.cmu.edu (John Snyder)
Newsgroups: sci.materials
Subject: Re: Insulator with good heat conductivity
Date: 28 Jul 92 07:53:19 GMT
Article-I.D.: fs7.1992Jul28.075319.9973
Organization: Physics Department, Carnegie Mellon University

In article <7926@dirac.physics.purdue.edu> parks@gibbs.physics.purdue.edu (Chris Parks) writes:
>
>What is a good material (good=price + availability) which is
>an electrical insulator and a good conductor of heat?
>
>It will be used at temperatures as low as 4.2 Kelvin and it needs
>to hold up to about 200 volts / mm, heat conductivity needs to
>be comparable to copper.  Does it exist?
>
>Note: Diamond may be ideal but not practical!
>
>Chris Parks
>parks@physics.purdue.edu


Sapphire has been mentioned to me as such a material.  You do not mention in
what form: shape, size this material must be or how much of it you need.  
I believe that you can get man-made sapphire substrates.  They are probably
not cheap, but surely cheaper than diamond.

For cryogenic temperatures, you could try intrinsic silicon (at low
temperatures, it is a very poor electrical conductor (not enough
energy to put any electrons up into the conduction band).  I believe
that most of the heat conduction in silicon is carried by phonons
(lattice vibrations), however, so it should still be a fairly good
conductor of heat (I once saw figures comparing thermal conductivities
of silicon doped at different concentrations, and the thermal conductivity
did not vary much).  Silicon might be one to think of also, since it has
the diamond structure, and is just below diamond in the periodic table.

Hope this helps

John
snyder@henry.ece.cmu.edu
Newsgroups: sci.materials
From: connor@nexus.yorku.ca (James Connor)
Subject: Re: Building Demolition Technology??
Organization: York University
Date: Thu, 23 Jul 1992 02:03:16 GMT

endacott@kuhub.cc.ukans.edu writes:

|Our Director of Support Services poses an interesting question.  I
|would appreciate any information related to improved technology for
|building demolition or leads to any research in process dedicated to
|this subject. I will summarize any direct mail back to the list.

|If we can disolve gall stones in a quiet fashion, without destroying
|"neighboring" tissue, perhaps we could disolve concrete/mortar/steel
|with this same or similar technology and just "flush unwanted
|buildings right down the drain!"  No fuss, muss, or noise pollution!!

|Any related information will be appreciated. . . . Phil---

 The 'gall stone' allusion gives me an idea...why not use some form of 
 ultra/infrasound to do the job...there are numerous quasi-scientific
 (and pseudo-scientific) books that purport to describe such technology,
 what does the orthodox physics community think ??


jcr



















Xref: sparky sci.materials:586 sci.electronics:13688
From: kwg@creare.COM (Kent Goeking)
Newsgroups: sci.materials,sci.electronics
Subject: Negative resistance
Date: 30 Jul 92 13:15:55 GMT
Reply-To: kwg@creare.UUCP (Kent Goeking)
Followup-To: sci.materials
Organization: Creare Inc., Hanover, NH


   I would like to know if there are any materials that demonstrate negative
   resistance on the macroscopic scale.  I am aware of this behavior in tunnel
   diodes but I wonder if it might not occur in other structures. 

   For example, it seems plausible to me that the conductivity (albeit small)
   of a dielectric material may be sensitive to the electric field in unusual
   ways.  If leakage currents are primarily carried along grain boundaries then
   perhaps if the material was piezoelectric, under a field these current paths
   might become more restricted due to increased internal stresses.  Hence the
   resistance would increase with applied field.  A plot of V vs I in this case
   would have negative slope and thus Ohms law would be rewritten V=-IR.

   Anyone know of such a material?  Is it possible to design some sort of
   composite?  Not sure what applications it would be good for but sure would
   be a unique capability.




-- 
^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~
Kent Goeking (kwg@creare.com)| "We are continually faced with a series of
Creare Inc., P.O. 71         |  opportunities brilliantly disguised as
Hanover, New Hampshire 03755 |  insoluble problems"  - John W. Gardner
From: stanb@hpnmdla.sr.hp.com (Stan Bischof)
Newsgroups: sci.materials
Subject: Re: Insulator with good heat conductivity
Date: 29 Jul 92 15:05:03 GMT
Organization: Hewlett-Packard, Santa Rosa, CA

In sci.materials, whit@milton.u.washington.edu (John Whitmore) writes:

Sorry, but I have to disagree with two of your points:

>	If your electricity is in superconductors, 'insulator' is a fair
>description of copper...

Copper is an excellent conductor at cryogenic temps, by any definition.
Please no pedantic drivel like ' compared to ZERO resistivity, anything
is infinitely less conductive and hence an insulator'.

>but 113W/cm/K at helium temperature.  Except for diamond, your
>best bet is BeO (highly toxic, by the way!) but the only data I have
                  ^^^^^^^^^^^^^^^^^^^^
Nonsense. This is pure urban legend. You could eat BeO on your breakfast
cereal and have no problems.

The only problems with BeO come in when you powder it very finely and 
inhale it into your lungs. The small particles cause some nasty reactions
similar to what happens with inhaled asbestos. Basically a mechanical
irritation. 

Stan Bischof
SRSD

*************************************************
Merely my own opinions, in no way related to the
opinions of my employer, Hewlett-Packard
*************************************************
From: rbradley@polaris.cv.nrao.edu (Richard Bradley)
Newsgroups: sci.materials
Subject: Re: Insulator with good heat conductivity
Date: 28 Jul 92 14:33:59 GMT
Distribution: na
Organization: National Radio Astronomy Observatory

Crystalline quartz is a good electrical insulator and a good thermal 
conductor at cryogenic temperatures.  Its thermal expansion coef. matches
that of copper so it will not crack upon cooling.  It is relatively
inexpensive and is available from a number of companies.  We use it
as a thermal strap for the center conductor of microwave coaxial cable.

Hope this helps.
From: jms@central.cis.upenn.edu (Jonathan M. Smith)
Newsgroups: sci.crypt
Subject: On Congruential Generators
Summary: Good References
Date: 30 Jul 92 12:45:40 GMT
Organization: University of Pennsylvania

Try either:

"How to Predict Congruential Generators", Hugo Krawczyk, in Advances in
Cryptology - CRYPTO '89 (Springer-Verlag LNCS #435), pp. 138-153

or:

"Inferring Sequences Produced by Pseudo-Random Number Generators", Joan
Boyar, J. ACM, V. 36, N. 1, 1989, pp. 453-461

						-Jonathan
Newsgroups: sci.crypt
From: bill@chaos.cs.umn.edu (Hari Seldon)
Subject: Re: Keeping track of a lot of passwords
Organization: University of Minnesota
Date: Thu, 23 Jul 1992 02:16:51 GMT

In <5006@transfer.stratus.com> cme@ellisun.sw.stratus.com (Carl Ellison) writes:

>In article <62453@cup.portal.com> ts@cup.portal.com (Tim W Smith) writes:
>>My current scheme is to have a file that lists the various passwords
>>I am using.  This file will be encrypted with a password that is *NEVER*
>>*EVER* used for anything else, and *NEVER* *EVER* written down anywhere.
>>Perhaps this file will even be kept off-line.  How does this seem?


>This sounds like an opportunity for some calculator company (probably
>Japanese).

>I can see having a password file in the continuous memory of a hand-held
>computer which I carry with me at all times.
oh! i thought this was already done. i do. and i wrote a small rng to 
get new ones with. and the code for it all is in a wierd jumping off
point in the hh. so you need to know where to jump to to start the thing.
it's not perfect but it helps.
i'd considered putting it in my sons pc jr but some day .....

bill pociengel
--
bill@chaos.cs.umn.edu
Newsgroups: sci.crypt,comp.security.misc
From: dhesi@cirrus.com (Rahul Dhesi)
Subject: Re: Crypt should be based on MD5 (was: the Crypt 16 discussion)
Organization: Cirrus Logic Inc.
Date: Thu, 23 Jul 1992 01:30:37 GMT

Some general comments about password expiration.   Assumption: the
intruder is trying to guess a password by already having access to the
encrypted form.

Suppose T1 is the time it takes for the intruder to determine a password
by some sort of search (guessing, exchaustive, whatever).  Suppose T2 is
the time it takes for an intruder to actually *begin using* a password
once he has guessed it.  So if the intruder acquires an encrypted
password at time t0, he can begin using it at time t0 + T1 + T2.

It makes sense to set the password expiration period to be less than T1 +
T2.  Then, by the time the intruder is ready to use the password, it has
been changed.

So what are useful values for T1 and T2?

My guess is that T2 can be as little as 15 seconds, the time it takes to
log in.

For well-chosen Unix passwords T1 is at least decades, if not several
centuries.  We need to expire a password in (some decades + 15 seconds).
It should be reasonable to expire a password in about a year.

For *poorly* chosen passwords, T1 might be as short as a day.  In that
case, passwords should expire every few hours.

CONCLUSION 1:  If passwords are well-chosen, password expiration adds
nothing to security.  If passwords are poorly-chosen, password expiration
must occur too rapidly to be of much use.

However, consider the intruder's point of view.  If the intruder can
immediately get access to the encrypted form a password when it is
changed, then password expiration becomes irrelevant.  Mathematically
speaking, if the intruder is always trying the *current* encrypted
password, his chances of guessing it neither increase nor decrease if the
encrypted password changes every 6 hours (or however often).

CONCLUSION 2:  If the intruder has immediate access to changed encrypted
passwords, then password expiration has no beneficial effect at all.

FINAL CONCLUSION:  Password expiration sounds good, may impress
customers, and certainly makes a sysadmin feel powerful and in control
(the VAX/VMS syndrome).  But it's far, far better to use a "passwd"
program that doesn't allow poor passwords in the first place.  And if you
do so, shadow password files aren't really needed, though they are still
a good thing.
-- 
Rahul Dhesi <dhesi@cirrus.com>
also: dhesi@rahul.net
"He's metabolically challenged, Jim."
From: brnstnd@nyu.edu (Dan Bernstein)
Newsgroups: sci.crypt
Subject: Re: New record non-networked factorization of difficult number
Date: 25 Jul 92 14:53:04 GMT
Organization: IR

In a reply to Bob Silverman I wrote:
> (2^488 + 1)/257 had 146 digits, last I counted.

Which proves once and for all that number theorists can't count. :-)
The factorization is still the record non-networked factorization, of
course, but (2^488 + 1)/257 has only 145 digits. While I'm at it let me
correct my assertion that 2^512 + 1 is the record difficult number; the
record difficult number is (2^512 + 1)/2424833, which has 148 digits.

In case anyone's wondering, I was misled by the UNIX dc program, which
acts like this:

% dc
2 488^ 1+ 257/p
310960166879725296199878945847101390767175534833553546544725362515212\
1265127859917318281565697486165824574686253229943428928722855633467075\
526401
10 145^p
1000000000000000000000000000000000000000000000000000000000000000000000\
0000000000000000000000000000000000000000000000000000000000000000000000\
000000

Notice how the first line of output is chopped off a digit early. This
is what I get for counting digits with the help of a computer instead of
by hand.

---Dan
Newsgroups: sci.crypt
From: mike@maria.wustl.edu
Subject:  Warning: naive question about /etc/passwd encryption
Date: Tue, 21 Jul 92 19:37:36 CDT
X-Received: by usenet.pa.dec.com; id AA03374; Tue, 21 Jul 92 17:49:22 -0700
X-Received: by inet-gw-1.pa.dec.com; id AA09806; Tue, 21 Jul 92 17:49:21 -0700
X-To: sci.crypt.usenet


I am a complete novice at cryptography and DES and all that stuff.

I have a (somewhat) hypothetical situation here.  Suppose I know
(or guess) that a user uses the same password on two different 
Unix systems and I have access to an unshadowed /etc/passwd.
Of course, the two encrypted entries for this person's password are
different on the two machines, but I know that the person uses the 
same password.  Does this make it more than twice as likely that I
could find out what this person's password is armed with this knowledge?
How does this extend to -- say -- 10 different encryptions on 10
different systems of the same password?

Please reply by email as my Usenet access is unreliable (and why I am
using a mail-news gateway to post).

-Mike
mike@maria.wustl.edu
Newsgroups: sci.crypt
From: jac54@cas.org ()
Subject: Another aspect of DNA and cryptology
Organization: Chemical Abstracts Service, Columbus, Ohio
Date: Wed, 22 Jul 1992 10:24:55 GMT

	In the most recent issue of Nature (9 July '92) John Maddox
	discusses a paper from Physical Review Letters (vol. 68, 3805)
	in which a mysterious property of the information content of
	DNA is studied: long-range correlations in nucleotide sequences.
	To put it another way, pieces of information separated by a lot of
	other (related) information affect one another.

	The correlations were found using a random walk model in four
	dimensions and they have a '1/f noise' character.

	This reminded this amateur cryptologist of looking for repeated
	n-graphs to identify the period in a polyalphabetic cipher.  So the
	following questions come to mind:

	Could such an approach be used to identify large numbers used as
	superencipherments?

	Any particular reason why not?

	If you have technical questions, please check the original
	documents, the analysis is certainly is not my field.

	Alec Chambers.

If these are my organization's opinions, I'd be extremely surprised.
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
<Alec Chambers (jac54@cas.org)  + Americans are a broad-minded people. They'll>
<Associate Editor, CAS          + accept the fact that a person can be an     >
<Phone (614)-447-3600 ext. 3992 + alcoholic, a dope fiend, a wife-beater, and >
<                               + even a newspaperman, but if a man doesn't   >
<Unsolicited Mail:              + drive there's something wrong with him.     >
<P.O.Box.21368                  +                                             >
<Upper Arlington                +  Art Buchwald.                              >
<OHIO 43221-0368                +                                             >
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Newsgroups: sci.crypt
From: lewis@aera8700.mitre.org (Keith Lewis)
Subject: Re: RSA Public Key Generations.
Organization: The MITRE Corporation
Date: Wed, 29 Jul 1992 20:09:56 GMT

In article <avalon.712399566@coombs>, avalon@coombs.anu.edu.au (Darren Reed) writes:
>Hi, I've been looking at implementing RSA encrpytion and have found that
>generating the initial keys is a somewhat tricky.  The only algorithm
>I have found for generation the public key is:

[find large primes x and y]
>N = x*y
>p*s mod (x-1)(y-1) = 1
>
>and solve for p. :(
>
>Is there an easy way to solve this problem ?

p*s = 1 + c * (x-1) * (y-1)

Pick a value for c other than zero.

You are now solving for p and s.  Try to factor 1 + c * (x-1) * (y-1). You
don't have to factor it completely, just enough so that p and s are  both
large (greater than N ** 0.33333, for example).  If you can't, start over
with a different c.

I know this algorithm will work, but I cannot guarantee that it will be 
cryptographically strong.

Here's a better one.  I haven't taken the time to understand it myself; it's
from Phillip Zimmermann's PGP.  Context:  p=x, q=y, e=p, d=s.

First find a small e which has no factors in common with (p-1)*(q-1).
Then use inv(d, e, (p-1)*(q-1)) below to find d.  

void inv(unitptr x,unitptr a,unitptr n)
    /* Euclid's algorithm extended to compute multiplicative inverse.
       Computes x such that a*x mod n = 1, where 0<a<n */
{
    /*    The variable u is unnecessary for the algorithm, but is 
        included in comments for mathematical clarity. 
    */
    short i;
    unit y[MAX_UNIT_PRECISION], temp[MAX_UNIT_PRECISION];
    unit gcopies[3][MAX_UNIT_PRECISION], vcopies[3][MAX_UNIT_PRECISION];
#define g(i) (  &(gcopies[i][0])  )
#define v(i) (  &(vcopies[i][0])  )
/*    unit ucopies[3][MAX_UNIT_PRECISION]; */
/* #define u(i) (  &(ucopies[i][0])  ) */
    mp_move(g(0),n); mp_move(g(1),a);
/*    mp_init(u(0),1); mp_init(u(1),0); */
    mp_init(v(0),0); mp_init(v(1),1);
    i=1;
    while (testne(g(i),0))
    {    /* we know that at this point,  g(i) = u(i)*n + v(i)*a  */    
        mp_udiv( g(iplus1), y, g(iminus1), g(i) );
        mp_mult(temp,y,v(i)); mp_move(v(iplus1),v(iminus1)); mp_sub(v(iplus1),temp);
    /*    mp_mult(temp,y,u(i)); mp_move(u(iplus1),u(iminus1)); mp_sub(u(iplus1),temp); */
        i = iplus1;
    }
    mp_move(x,v(iminus1));
    if (mp_tstminus(x))
        mp_add(x,n);
    mp_burn(g(iminus1));    /* burn the evidence on the stack...*/
    mp_burn(g(iplus1));
    mp_burn(v(0));
    mp_burn(v(1));
    mp_burn(v(2));
    mp_burn(y);
    mp_burn(temp);
#undef g
#undef v
}    /* inv */

Keith Lewis             klewis@mitre.org          "Mr. Cheap"
I don't dance to music; music dances to me.  Email me for my corrected PGP key.
The above may not (yet) represent the opinions of my employer.
Newsgroups: sci.crypt
From: hal@gateway (Hal Feinstein)
Subject: Re: linear congruential RNG cipher (was: Re: Cypher algorithm question.)
Keywords: cipher linear congruential random number xor weak Knuth break
Organization: Mitre Corporation, McLean, VA
Date: Fri, 31 Jul 1992 12:49:51 GMT

In article <1992Jul31.034244.9150@chpc.utexas.edu> jonathan@chpc.utexas.edu (Jonathan Thornburg) writes:
>In article <tom.712397505@cluster> tom@stallion.oz.au (Thomas Essebier) writes:
>>By far not being an expert on cryptology, I would appreciate some 
>>comments on the crypto scheme below. 
>> [ use a standard linear congruential random number generator (= RNG),
>>   primed with the key, to derive a stream of bits, which is then xor-ed
>>   with the data ]
>>
>
>In general, the fundamental lesson of crypto history is that good
>cryptosystems are designed *only* by people who have both theoretical
>knowledge of, *and* practical experience with, breaking existing
>high-quality cryptosystems.  In other words, unless you have a lot
>of crypto experience you're unlikely to come up with a system that
>would withstand professional attack.
>
>
>- Jonathan Thornburg
>  University of Texas at Austin / Physics Dept / Center for Relativity
>  and (for a few more months) U of British Columbia / {Astronomy,Physics}


Not True. In fact the principle used by many cipher systems were invented by
invented by amateurs (as well as a lot of garbage).  It takes a 
professional to cast in into a framework were it will be strong. For example,
public key cryptography was not invented by professional codemakers.
It was originally invented by a student at Stanford. Experts took the 
principle and developed it into a strong system.

In contrast, it usually takes  profesional codebreakers to break a system.
Cryptanalysis doesn't seem to be a subject were amateurs thrive.

Newsgroups: sci.crypt
From: pmetzger@snark.shearson.com (Perry E. Metzger)
Subject: Re: Cypher algorithm question.
Keywords: question, algorithm, encrypt, crypt, decrypt
Organization: /usr/local/lib/news/organization
Date: Wed, 29 Jul 1992 15:50:03 GMT

In article <tom.712397505@cluster> tom@stallion.oz.au (Thomas Essebier) writes:
>By far not being an expert on cryptology, I would appreciate some 
>comments on the crypto scheme below. 

Linear congruential generator based schemes are very easy to break;
I've even heard Phil Zimmerman tell of encountering an intro crypto
class where breaking them was a homework assignment in the first week.
Everyone thinks them up at one time or another. One technique that
DOES work is a scheme similar to yours based on using
cryptographically strong RNGs, like ones the breaking of which is
equivalent to factoring large numbers. However, I should point out
that no one uses these techniques in practice for the same reason that
people only exchange keys using RSA and use conventional cyphers for
the real work -- too much computation time.

>Where does it stand in terms of security when compared to transposition 
>cyphers, DES etc.

DES is very hard to break. Transposition cyphers, well, that depends
on which one we are talking about.

>If anybody could point me to some literature that explains why the above
>is (un?)reasonably (in?)secure I would be most grateful. Please note that
>I make no claim to have carefully studied and researched this topic. 
>I was hoping to avoid all that :-)

I would suggest that you read some intro to cryptography texts; it
would likely be quite rewarding; the topic is common enough.

--
Perry Metzger		pmetzger@shearson.com
--
		  Just say "NO!" to death and taxes.
			 Extropian and Proud.
Xref: sparky sci.crypt:2716 comp.security.misc:772
From: nelsonm@leela.cs.orst.edu (Michael Nelson)
Newsgroups: sci.crypt,comp.security.misc
Subject: Re: Crypt should be based on MD5 (was: the Crypt 16 discussion)
Date: 22 Jul 92 20:37:46 GMT
Article-I.D.: leela.1992Jul22.203746.10010
Distribution: usa
Organization: Computer Science Outreach Services - Oregon State University

In <62451@cup.portal.com> ts@cup.portal.com (Tim W Smith) writes:

>Has anyone shown that forcing users to change passwords every so often
>actually makes things more secure?  Isn't frequent changing of passwords
>just going to make it more likely that users will write down the passwords
>somewhere?

I have a real example of how changing the password very month can
lower security.

I have a friend that has to change the password every month, and can't
reuse passwords.

His solution was simple.  91Jan 91Mar 91Apr and so on.  

>--Tim Smith
Newsgroups: sci.crypt