🚀 go-pugleaf

gjb@fig.citib.com (Greg Brail) writes:

[... deleted ...]

: So -- as I've come to expect from Hollywood, most of the technical
: details in the book (and I assume the movie), are either impractical,
: impossible, or nonexistent. (There are a few neat tricks shown, however.)
: But let's assume someone does figure out how to trivially factor very
: large numbers. I understand that would defeat RSA. Am I correct? 

Yes.  The decryption key is trivially obtainable from the factors of
the public modulus.

: How about DES? 

No.  DES does not use problems in number theory.

: Are other common government and commercial cryptosystems based on
: large primes? I assume that one-time pads would still be quite effective.

Certainly.  Some cryptosystems (e.g. the proposed NIST signature
standard) are based on the discrete logarithm problem, which is
generally thought to be of similar difficulty to factoring large
primes.  It is possible that any breakthrough in number theory which
broke RSA could also be used to perform discrete log.

One time pads will always be effective.

: And how about this "Russian codes are different" stuff? Any truth to this?

No idea.

: I understand one can buy source code for DES and RSA on the streets of
: Leningrad (according to Communications of the ACM).

Source code is available by anonymous FTP.  Anyone with anonymous FTP
access in Leningrad could pick it up for free.  Papers discussing
efficient algorithms are freely available worldwide.

: Someday someone will produce a computer-cracking scene in a movie that
: looks as if the people involved have logged in to a system via a modem
: at least once in their lives. I don't think "Sneakers" will be it.
: 
: 				greg
: 
: P.S. If no one agrees that the technical details in this movie are silly,
: I'd be glad to post more.

I agree, it's silly.   Please, no more!  :-)

Andrew.

P.S.  Aren't the actors in the movie a little old to be hackers?

gjb@fig.citib.com (Greg Brail) writes:
>Universal Pictures will soon release (at least in the U.S.) a movie called
>"Sneakers" that purports to be an action/adventure starring a group of
>free-lance computer security consultants. The plot centers around a
>cryptographic device. For whatever reason, I bought the book (actually
>the "novel based on the screenplay"). It was already at a Barnes and Noble
>Sale Annex in Manhattan, which might indicate how well it's selling.

Hey, but the movie looks like a good one! Just remember to only watch the
characters and ignore the technical details like in "Wargames" and half-a-dozen
other 'hacker' movies.

>But let's assume someone does figure out how to trivially factor very
>large numbers. I understand that would defeat RSA. Am I correct? How about
>DES? Are other common government and commercial cryptosystems based on
>large primes? I assume that one-time pads would still be quite effective.

DES is a seperate system that doesn't rely on Factoring large numbers or large
primes (or at least that's what a friend of mine, an expert on this stuff he
claims, told me). One-time pads are so effective that according to Tom Clancy
(can he really be telling the truth?) that they have converted to using Digital
tapes that contain the 'pad'. Any tampering with the seal means all pads of
that line are destroyed. Anyways, one-time pads are really effective in short
messages and are reasonably secure on larger documents.

>And how about this "Russian codes are different" stuff? Any truth to this?
>I understand one can buy source code for DES and RSA on the streets of
>Leningrad (according to Communications of the ACM).

Russian Codes still use one-time pads. See the above paragraph.
-- 
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>>Anyways, one-time pads are really effective in short
>>messages and are reasonably secure on larger documents.

Arguably this is backwards. As suggested in "Codebreakers",
if I suspect that a "yes" or "no" decision is forthcoming, and I 
intercept a 3 character long message, I can make a reasonable
guess as to the message's contents.

More generally, "traffic analysis" is still a threat.  So some systems
send continuously, just sending nulls or-ed with the pad
(== the pad itself) when there is no real traffic.

In <715637499@romeo.cs.duke.edu> trt@duke.cs.duke.edu (Tom Truscott) writes:

>>>Anyways, one-time pads are really effective in short
>>>messages and are reasonably secure on larger documents.

>Arguably this is backwards. As suggested in "Codebreakers",
>if I suspect that a "yes" or "no" decision is forthcoming, and I 
>intercept a 3 character long message, I can make a reasonable
>guess as to the message's contents.

nope, 'cause even the book I have on crypto written for 10-year-olds
says to pad your messages out to groups of five....

sotha ttraf fican alysis isnot asbig athre atasi tcoul dbexx

>More generally, "traffic analysis" is still a threat.  So some systems
>send continuously, just sending nulls or-ed with the pad
>(== the pad itself) when there is no real traffic.

This is doubly true, however.  Everybody who's been around knows that when
there are pizza delivery trucks headed for Foggy Bottom, Something Big is
going down.... a very simple "traffic analysis".  

Anything remotely resembling good code won't reveal the actual number of
characters in the message exactly; really good stuff, a la above, sends
synchronously and uses framing characters or some such...  on the other
hand, if you stumble onto something sending async, you can always tell
when something's going on when the message traffic goes way up... ;)

-- Glenn R. Stone (glenn.stone@eas.gatech.edu)
Nazi conservative Quayle NSA coverup watergate CIA breakin nuclear gun drugs