textfiles/programming/CRYPTOGRAPHY/code.txt

                            Cracking the Code
                            By: Mark D. Uehling


Last April, detectives in San Diego stunbled upon a national network of about 
1,000 computer hackers who had breached more than the conventional password-
related defenses of banks and credit card companies.  In the months after
the first arrests in California, police caught ringleaders in New York, Florida,
Arizona, Pennslyvania, Washington, and Ohio.  Among other financial data, the 
hackers had illegally divined the personal identification numbers used in 
automated teller machines.  These numbers are encrypted with a special federally
approved scarambling formual intended to protect the customers of every bank.
But the hackers were able to thwart that encryption.  They even used other
scrambling techniques to hide their own records from police.  "The hackers have
their own encryption system that is probably better than any at IBM," says 
Dennis Sadler, the San Diego detective in charge of the case.

Banking identification numbers depend on the sort of scrambling code used to
generate the gibberish displayed on Robert Redford's computer screen in the 
movie Sneakers.  This code can garble any form of information--words or numbers--
stored as computer data.  It can prevent eavesdropping on telephone conversations,
keep facsimiles out of the wrong hands, and safeguard radio broadcasts.  Crop
reports at the U.S. Department of Agriculture are encrypted with it.  So are
Nintendo cartridges and money (most funds move from one bank to another via
computers, not armored cars).

The original name of the devilishly versatile code was Lucifer.  At IBM, where
the formula was devised early in the 1970's, executives despaired of profiting
from Lucifer and released it to the public domain.  The U.S. government, which
has long collaborated with IBM, tinkered with the code and renamed it the Data
Encryption Standard, or DES.  Aware of the many illicit uses to which sensitive
government information could be put, Congress mandated DES encoding for federal
computer files.  It was adopted as a national standard in 1977.  With government
approval, DES gained wide public use first in banking and more recently in
personal computers and facsimile machines.

Fortunately, considering the stakes, most cryptographers have complete faith
in the code, believing it will never be cracked.  To the credit of IBM and its 
allies in the intelligence agencies, a generation of mathematicians have spent
their careers trying to break DES without success.  While other codes fell to
one mathematical attack or another, DES remained invulnerable, invincible,
uncrackable.

Now, however, that impressive record seems destined to end.  The speed of 
integrated circuits has grown at a fantastic rate, and it is not impossible to
envision a day when supercomputers will be powerful enough to search all possible
passwords for the key to a DES message.  "All cryptography has a natural life
span, and advances in technology will reduce the security provided by DES in
the future," concedes Michael S. Conn, chief of information policy at the 
National Security Agency (NSA), a Pentagon division devoted to electronic
espionage.

The federal government recognized the vulnerabilities of DES in 1988, when the 
NSA decertified DES for classified purposes within the government.  For the
customarily silent espionage establishment, that was a shotgun blast alerting 
the computer industry that DES was no longer wholly reliable.  By then, however,
American banks had adopted DES so completely that some form of federal approval
was demanded by the business community.  The Commerce Department obliged, 
reapproving DES.  However, Commerce's reputation for world-class code-making is
weaker than that of the NSA, which has more cryptographic brain power than
any university in the world.

One possible reason why the NSA souded the alarm about DES is because the code
is so well known.  As Conn of the NSA explains: "Government use of DES equipment
has spread to applications making [DES] increasingly attractive as a potential
target for adversaries of the U.S. government."  Indeed, unlike the classified
cryptography used for top-secret military plans and the Oval Office telephone,
DES is an open book.  Its workings have been described in official U.S. 
government publications and countless technical articles.

In basic DES procedure, a letter or document is converted into numbers.  These
numbers are then replaced and reordered using numbers selected from a key--a
password-like number chosen by the person encrypting the message.  The
substitution and reordering occur gradually so that the message and the key
are thoroughly mixed.  The resulting number is then scrambled again and again,
for a total of 16 rounds of manipulation.  By the end, a phrase such as "Cancel 
Plan B!" becomes 3102 5896 4807 1192 5046 1891 0288.  The numbers can only
be converted back into "Cancel Plan B!" if they are put through the same 
scrambling operation in reverse order, using the same key.

A DES key is 56 binary digits long.  In the world of computers, each digit can
be either a one or a zero, so the number of possible keys that can be used is
two raised to the 56th power.  That works out to 72,057,594,037,927,936 different
ways to encode a message with DES.

Cryptographers haggle over how much time is needed to plow through these
72 quadrillion passwords.  Some say a month; others believe it could be done
in a few hours on a supercomputer dedicated to the task.  "There must be
thousands of computers that could succeed with a brute force approach,"muses
David Stang, research director of the National Computer Security Association.
"A desktop computer you can buy for $20,000--maybe it sits on the floor by your
desk--is certainly as powerful as anything the National Security Agency owned
a decade ago when the standard was first discussed.  And a desktop computer could
succeed in some cases."  Thanks to faster silicon chips, parallel processing,
and ever-better supercomputers ["The Teraflops Race," March '92], even those
with faith in DES agree that some day soon DES keys will be searched and tested
with ease.

What's more, 16 rounds of substituting and reordering may not be enough to 
protect a message from prying eyes.  In 1974, when DES was first publised 
in the Federal Register, 16 rounds seemed more than sufficient.  But as many
cryptographers have shown, sometimes informally at conferences, they can track
messages through three-quarters of those rounds before getting lost in the maze
of numbers.  "There are theories that you can break a 12-round data encryption 
scheme without a tremendous amount of trouble," says Gary S. Morris, a Pentagon
consultant on information security.

It was against this backdrop that a gifted but self-promoting mathematician
named Adi Shamir stepped forward in the fall of 1991 to announce he had discovered
a "weakness" in DES.  Shamir, a professor at Israel's Weizmann Institute of 
Science, distributed his tantalizing comments over an international computer
network.  In the close-knit world of cryptography, the announcement was big
news; today the presence of Shamir's finding is about as widely known as DES
itself.

Collaborating with graduate student Eli Biham, Shamir developed a technique
called "differential cryptanalysis."  The technique currently has little 
practical application in breaking DES, but it outlines a method for discovering
a DES key without trying all of the 72 quadrillion possibities.  In essence,
Shamir claims that once he is given enough messages encrypted with the same
DES key, he can detect a pattern that will allow him to decipher other 
messages.

"Computers are hundreds or thousands of times more powerful than they were
when DES was first developed," says Nathan Myhrvold, vice president for 
advanced technology at Microsoft Corp.  "Shamir's work makes it potentially
feasible to break DES without brute force.  DES doesn't afford the same measure
of security [as it once did]."

For now, though, DES appears to be safe from Shamir's attack.  Although his
technique is a shortcut that makes it unnecessary to test 72 quadrillion
passwords, there's a hitch: To identify a DES key, Shamir must first obtain
several trillion messages encrypted with that key, as well as the original
texts.  That requirement makes it exceedingly difficult for im to crack the
code.

A top IBM research scientist, Don Coppersmith, who worked on DES in its early
days says the company anticipated Shamir's analysis more than 15 years ago, in
the mid 1970's.  According to Coppersmith, the DES formula is strong enough to
withstand the attack.  Shamir's technique won't work, Coppersmith maintains, 
unless a code-cracker can either persuade his enemy to encrypt an unimaginable
quantity of data, or commandeer his enemy's computer.  If Joe Q. Hacker wanted
to identify a DES key used by the First National Bank in Chicago, he would have
to take control of the bank's computers for months or years.

On a theoretical level, Coppersmith syas, the IBM team anticipated a hacker
who might try to break DES by analyzing differences in the enciphered versions
of two similar messages.  To do so, the hacker would need to detect a faint
pattern of differences after each of the 16 rounds of encryption.  By finding
that pattern, in theory, a hacker might be able to identify part of the DES key--
and quickly calculate the rest.  However, says Coppersmith, "the probability
of finding any one of these patterns is enormously small."  At best, he says
it's one in one quadrillion.  Discerning the pattern through trial and error
would require an astronomical number of calculations, as Shamir himself admits.
A code-cracker simply wouldn't have time to perform the calculations on the
targeted computer.

No matter how the scientific community assesses the Shamir attack, there are
two other problems with DES that have spurred the search for a new standardized
code.  The biggest obstable to using DES is that the sender and the recipient of
an encrypted message must somehow share the key.  Mentioning it on the telephone
is unwise; a novice detective could intercept the key with inexpensive gear
from Radio Shack.  Mail services can be subverted with equal ease.  Large
companies have been reduced to using trusted couriers; some departments in the 
U.S. and Canadian government have spent millions of dollars a year using such
messengers.  However, couriers are out of the question for a sender and a 
recipient who have never met: The recipient has no way of ascertaining whether
the DES key and message are genuine.

Worse, many cryptographers in academia and industry have long suspected that 
the government can already break the widely used DES code.  Its motive: to 
intercept the communications of foreign governments, terrorists, or the Mafia.
The government has long denied this ability exists, as does IBM.  But the NSA's
expertise in cryptography is so esteemed, so revered, that many cryptographers
assume the government can devote a supercomputer or a battalion of analysts
to cracking an important DES key.

"Undoubtedly the U.S. government knows how to break DES," says Harold J. Hyland,
editor emeritus of the journal Computer Security and a former intelligence
officer.  "The people capable of breaking it could never publish it.  They work
for the government or in academia.  If you did find a way to break it, you'd 
find it very hard to get funding."  Many in the field share Hyland's view and
cite the government's role in the birth of DES--when, at the NSA's request,
IBM shortened the original key.  That made DES easier to break.

The skepticism over DES intensified when the Commerce Department's National
Institute of Standards and TEchnology (NIST), guided by the NSA, proposed a
new standard in 1991--a so-called digital signature--for verifying and 
authenticating any electronic document.  Shortly after the government proposed
its method, a pair of mathematicians at Bellcore, the research arm of the 
regional Bell telephone companies, announced several shortcomings.  The bottom
line:  Under the new proposal, the government might be able to forge any
signature or read any document.

"Their proposal had a number of things wrong with it," says Bellcore mathematician
Stuart Haber.  Speaking of a hypothetical bureaucrat, he adds: "If he does
a very simple bit of arithmetic, he can check whether his guess is correct.
He gets the message and he gets your key from then on.  You don't need very
sophisticated techniques to mount this attack."  The government has not 
responded to the Bellcore objections, adding to speculation about Orwellian
intentions.

Given concerns about DES and the government's motives, the computer industry
is trying to agree on a new standard without the official backing of the 
government.  The system eliciting the most interest is a method of encryption
that does not depend upon easily intercepted exchange of a password.

Many of the largest computer hardware and software companies have already 
licensed the RSA Public Key Cryptosystem, which can be used in concert with DES.
RSA is named after its inventors--Ronald L. RIvest, a computer scientist at
the Massachusetts Institute of Technology (MIT);Shamir; and Leonard M. Adleman,
a mathematics professor at the University of Southern California who recently
served as a consultant for Sneakers.  All three were professors at MIT when 
they devised the system in 1977.  The university licensed the patent to
them in 1982, and they formed RSA Data Security in Redwood City, Calif., to
market the technology.

TWO KEYS ARE BETTER THAN ONE

Instead of a single key that must be shared between users, the RSA system has a 
matched pair of keys.  One key is private, and the other is public.  The public
key is published in a directory, allowing people who have never met to send 
messages to each other.  The public and private keys perform inverse functions:
What one does, the other can undo.

Under the RSA protocol, as with DES, a document is first converted into numbers.
Using the public key, these numbers are rased to frighteningly high exponential
powers and divided by the product--at least 150 digits long--of two prime
numbers.  The remainder of the fraction is the encrypted bit of information.
Only someone with the private key, which contains the two prime numbers, can 
compute the remainder and decode the message.

The system relies on the difficulty of factoring a large number back to two
prime numbers--numbers that can be dvided evenly only by the number 1 and 
themselves (3,5,7,11, and so on).  It is easy to multiply two large prime 
numbers together, but hard to factor their product back to its two components.
In October 1988, for example, it took an international group of computer
scientists nearly a month to factor a 100-digit number.  More than 400 computers
worked on the problem during idle hours to find the number's two factors--one
41 digits long, the other 60 digits long.  In June 1990, another team factored
a 155-digit number.  The number was handpicked to make the task easier, but it 
still took 275 years' worth of computer time.  To keep pace with ever-faster
computers, RSA's inventors can simply add more digits to the system's keys.

RSA and DES are not competitors.  In fact, RSA could help prevent DES from
becoming obsolete.  Because it takes a long time to encrypt an entire message
with RSA, the system is typically used to encrypt a DES key.  That key is then
used to encrypt the rest of the message.  "RSA lets you use a different DES
key for every message," explains James Bidzos, president of RSA Data Security.

A NEW GOVERNMENT STANDARD?

In the coming months, NIST will decide whether DES will remain as the standard
encryption method used by the federal agencies.  Because the new "digital 
signature" standard proposed by NIST is under fire, the Commerce Department's
computer security advisory board has recommended that the standards institute
delay its decisions until June of this year.

The computer industry would like NIST to adopt the RSA technology, but that 
isn't likely to happen.  One reason: If the privately developed technology 
becomes a standard, the government will have to pay royalties for its use.
And perhaps more important, the NSA does not want the government to back the 
RSA encryption system.  The agency has already conducted private negotiations
with the Software Publishers Association, which represents computer software
makers, regarding the export of programs containing encryption features.

"[The NSA] dislikes our system because it's too hard to break," says Bidzos.
"They clearly don't like what we do, but we're succeeding in spite of that."

The power of RSA's approach has already spread, through unknown channels, to
foreign enemies.  Iraqi generals are believed to have used RSA encryption
during the Persian Gulf war, and the technology is indisputably on the move
throughout the world.  Perhaps the only good news is that American generals 
had the same RSA technology in their laptop computers.

This article appeared in the January 1993 Popular Science, Vol 242, No. 1.
It was on pages 71-74,84.

Cobra

read any document.

"Their proposal had a number of things wrong with it,