From: john@anasazi.com (John R. Moore)
Subject: Re: 800MHz Trunked Radio System Signals
Reply-To: john@anasazi.com
Organization: Anasazi, Inc.  Phoenix, Arizona USA
Date: Sat, 2 Jan 1993 02:14:29 GMT

Keywords: 

In article <1993Jan1.225759.15962@timesink.chi.il.us> mikebo@timesink.chi.il.us (Michael Borowiec) writes:
]You are mistating yourself. I said you couldn't outlaw a "THING"
](object), only the USE of that "THING" (object). You said I was
]wrong, and then proceeded to validate what I said... the law outlaws
]the ACT of intentional reception of encrypted signals. Note that the
]mere possession of the such receiving equipment is NOT ILLEGAL. It's
]been my observation that only very few things (objects) are illegal
]to possess, such as drugs and dangerous weapons.
It is indeed possible to outlaw a thing, as you demonstrate. It is
possible to outlaw, for example, scanners. Fortunately it hasn't
been done nationwide.

]>Yes, DES is relatively secure. However, the most recent cryptography research
]>that I have read about claims that they believe DES is about as secure as is
]>possible with a 56 bit key. That means you need an exhaustive key search
]>(2^56 keys). At 100 Mips, you could figure maybe 100,000 tries per second?
]>That would yield 548 YEARS of decryption time. Now, it is ALLEGED that the
]>NSA eats DES messages for lunch, but I would point out that 20 million dollars
]>for a specialized computer is peanuts to the NSA. I doubt they eat them
]>for lunch with a few 100 MIPS computers!
]>
]Where do you get this $20M number from, out of thin air?

No, out of a report on the estimated cost to decrypt DES. It comes from
estimating how much it would cost to develop specialized chips for cracking
DES, and then building a massively parallel processor (millions of MIPS!)
to do the key search. Since no one has found a practical way to significantly
reduce the size of the key search, this is not an unreasonable estimate.
]
]Have you seen the latest "Crack" program? As the system admin, I was
]interested in how secure password encryption was. I ran "Crack" on my
]password file and it busted over 60% of the DES encrypted passwords
]on my systems within a week on a mere 33Mhz 386. These were not all
]dictionary words either. Sure, this is a super easy example... but
]the same techniques can be used to crack any encrypted plaintext.

Crack does not decrypt DES. As I understand it, it generates likely
passwords and then ENCRYPTS them (the encryption algorithm is known) and
compares the results. By the way, UNIX password encryption is NOT DES,
although it is related to it.

There have been plenty of people who are experts in cryptography who
have been trying for years to break DES. The have so far only been
able to determine that it is MORE secure than they thought, and in 
fact was generated using security ENHANCING techniques that were not
publicly known until the last few years, even though DES was invented
in the 70s.

If you think DES is practically breakable, try it. Better would be to
read what those far more knowledgable than myself or yourself have
been discovering about it. DES achieves its difficulty by two
techniques: it makes sure that every output bit is dependent on
almost every input bit and key bit; the cipher function (Key operating
on plaintext => ciphertext) is extremely nonlinear, resulting in
an extremely large number of min-terms in the cipher function, and
no known analytical solution. These principles are both used in modern
cryptography to produce the most secure ciphers.

There is no reason to believe that NSA would make DES weak, because they
can easily afford the specialized computer systems needed to break it
quickly, while very few other organizations can. This gives them an
advantage that is not vulnerable to a sudden discovery or a security link.

]>By the way, it is even more secure with voice encryption, because once you
]>have it decoded, how can you tell that you have the right plaintext? More
]>processing required. Most text info, on the other hand, is easier (letter
]>frequency tests, parity bit tests, etc).
]>
]Yup... I'm sure audio complicates things. But I don't believe in
]unsinkable ships or unbreakable codes. Never say never...  DVP presents
]some neat challenges. I have no doubt the NSA is already able to crack
]any system on the market. Much harder would be putting together spread
]spectrum with a shifting hop pattern.

Well, you are talking beliefs. Let's talk about facts. There IS
a well known unbreakable cipher (codes are a different thing): the
one-type cipher. This uses a randomly generated bit sequence which is
exclusive-or' with the plaintext/ciphertext to yield ciphertext/plaintext.
Since the cipher key is generated randomly (I mean truly randomly, such as 
radioactive decay counters, no pseudo-randomly), and each bit is used
only once, there is no way to decode a message enciphered this way
other than having a copy of the original cipher key. These ciphers can
be attacked on the basis that they are not generated truly randomly,
but it is not hard to generate one that is random enough to be
unbreakable. The only other attack is to steal the key. In a true
high security system, the key would be generated by a physically random
process and only two copies would be made (perhaps on CD ROM for large
volumes of data). One copy would remain in the possession of the sender
and the other in the possession of the recipient.

In theory, one time ciphers ARE ABSOLUTELY UNBREAKABLE. In practice,
they are also, except by stealing the key, or spoofing the key generator,
or other non-cryptographic attacks.

It is nice to have a faith that there are no unbreakable codes, but that
faith is no more accurate than a faith that the earth is flat.

-- 
John Moore NJ7E, 7525 Clearwater Pkwy, Scottsdale, AZ 85253  (602-951-9326)
john@anasazi.com ncar!noao!asuvax!anasaz!john anasaz!john@asuvax.eas.asu.edu
"Modern liberals are the termites in the structure of our society."
  John Moore
Xref: sparky alt.radio.scanner:3503 rec.radio.shortwave:9002