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Status: RO
User-Agent: Microsoft-Entourage/
Date: Thu, 23 Jan 2003 16:57:25 +0900
Subject: [IP] Master Key Copying Revealed (Matt Blaze of ATT
From: Dave Farber <[EMAIL PROTECTED]>

Master Key Copying Revealed

January 23, 2003

A security researcher has revealed a little-known
vulnerability in many locks that lets a person create a
copy of the master key for an entire building by starting
with any key from that building.

The researcher, Matt Blaze of AT&T Labs-Research, found the
vulnerability by applying his area of expertise - the
security flaws that allow hackers to break into computer
networks - to the real-world locks and keys that have been
used for more than a century in office buildings, college
campuses and some residential complexes.

The attack described by Mr. Blaze, which is known by some
locksmiths, leaves no evidence of tampering. It can be used
without resorting to removing the lock and taking it apart
or other suspicious behavior that can give away ordinary
lock pickers.

All that is needed, Mr. Blaze wrote, is access to a key and
to the lock that it opens, as well as a small number of
uncut key blanks and a tool to cut them to the proper
shape. No special skills or tools are required; key-cutting
machines costing hundreds of dollars apiece make the task
easier, but the same results can be achieved with a simple
metal file.

After testing the technique repeatedly against the hardware
from major lock companies, Mr. Blaze wrote, "it required
only a few minutes to carry out, even when using a file to
cut the keys."

AT&T decided that the risk of abuse of the information was
great, so it has taken the unusual step of posting an alert
to law enforcement agencies nationwide. The alert describes
the technique and the possible defenses against it, though
the company warns that no simple solution exists.

The paper, which Mr. Blaze has submitted for publication in
a computer security journal, has troubled security experts
who have seen it. Marc Weber Tobias, a locks expert who
works as a security consultant to law enforcement agencies,
said he was rewriting his police guide to locks and
lock-picking because of the paper. He said the technique
could open doors worldwide for criminals and terrorists. "I
view the problem as pretty serious," he said, adding that
the technique was so simple, "an idiot could do it."

The technique is not news to locksmiths, said Lloyd
Seliber, the head instructor of master-key classes for
Schlage, a lock company that is part of Ingersoll-Rand. He
said he even taught the technique, which he calls decoding,
in his training program for locksmiths.

"This has been true for 150 years," Mr. Seliber said.

Variations on the decoding technique have also been
mentioned in passing in locksmith trade journals, but
usually as a way for locksmiths to replace a lost master
key and not as a security risk.

When told that Mr. Seliber taught the technique to his
students, Mr. Tobias said: "He may teach it, but it's new
in the security industry. Security managers don't know
about it."

In the paper, Mr. Blaze applies the principles of
cryptanalysis, ordinarily used to break secret codes, to
the analysis of mechanical lock designs. He describes a
logical, deductive approach to learning the shape of a
master key by building on clues provided by the key in hand
- an approach that cryptanalysts call an oracle attack. The
technique narrows the number of tries that would be
necessary to discover a master-key configuration to only
dozens of attempts, not the thousands of blind tries that
would otherwise be necessary.

The research paper might seem an odd choice of topics for a
computer scientist, but Mr. Blaze noted that in his role as
a security researcher for AT&T Labs, he examined issues
that went to the heart of business security wherever they
arose, whether in the digital world or the world of steel
and brass.

Since publishing Mr. Blaze's technique could lead to an
increase in thefts and other crimes, it presented an
ethical quandary for him and for AT&T Labs - the kind of
quandary that must also be confronted whenever new security
holes are discovered in computing.

"There's no way to warn the good guys without also alerting
the bad guys," Mr. Blaze said. "If there were, then it
would be much simpler - we would just tell the good guys."

Publishing a paper about vulnerable locks, however,
presented greater challenges than a paper on computer

The Internet makes getting the word out to those who manage
computer networks easy, and fixing a computer vulnerability
is often as simple as downloading a software patch. Getting
word out to the larger, more amorphous world of security
officers and locksmiths is a more daunting task, and for
the most part, locks must be changed mechanically, one by

But Mr. Blaze said the issue of whether to release
information about a serious vulnerability almost inevitably
came down to a decision in favor of publication.

"The real problem is there's no way of knowing whether the
bad guys know about an attack," he said, so publication
"puts the good guys and the bad guys on equal footing."

In this case, the information appears to have made its way
already to the computer underground. The AT&T alert to law
enforcement officials said that a prepublication version of
the paper distributed privately by Mr. Blaze for review
last fall had been leaked onto the Internet, though it has
not been widely circulated.

"At this point we believe that it is no longer possible to
keep the vulnerability secret and that more good than harm
would now be done by warning the wider community," the
company wrote.

There is evidence that others have chanced upon other
versions of the technique over the years. Though it does
not appear in resources like "The M.I.T. Guide to
Lockpicking," a popular text available on the Internet, Mr.
Blaze said, "several of the people I've described this to
over the past few months brightened up and said they had
come on part of this to make a master key to their college

Mr. Blaze acknowledged that he was only the first to
publish a detailed look at the security flaw and the
technique for exploiting it.

"I don't think I'm the first person to discover this
attack, but I do think I'm the first person to work out all
the details and write it down," he said. "Burglars are
interested in committing burglary, not in publishing
results or warning people."

Mr. Tobias, the author of "Locks, Safes and Security: An
International Police Reference," said that the technique
was most likely to be used by an insider - someone with
ready access to a key and a lock. But it could also be
used, he said, by an outsider who simply went into a
building and borrowed the key to a restroom.

He said he had tested Mr. Blaze's technique the way that he
tests many of the techniques described in his book: he gave
instructions and materials to a 15-year-old in his South
Dakota town to try out. The teenager successfully made a
master key.

In the alert, AT&T warned, "Unfortunately, at this time
there is no simple or completely effective countermeasure
that prevents exploitation of this vulnerability, short of
replacing a master-keyed system with a nonmastered one."

The letter added, "Residential facilities and
safety-critical or high-value environments are strongly
urged to consider whether the risks of master keying
outweigh the convenience benefits in light of this new

Other defenses could make it harder to create master keys.

Mr. Blaze said that owners of master-key systems could move
to the less popular master-ring system, which allows a
master key to operate the tumblers in a way that is not
related to the individual keys. But that system has
problems of its own, security experts say.

Mr. Blaze suggested that creating a fake master key could
also be made more difficult by using locks for which key
blanks are difficult to get, though even those blanks can
be bought in many hardware stores and through the Internet.

But few institutions want to spend the money for robust
security, said Mr. Seliber of Schlage. His company
recommends to architects and builders that they take steps
like those recommended by Mr. Blaze, measures that make it
more difficult to cut extra keys - like using systems that
are protected by patents because their key blanks are
somewhat harder to buy, Mr. Seliber said. Even though such
measures would add only 1 to 2 percent to the cost of each
door, builders were often told to take a cheaper route. He
said that they were told, " `We're not worried about ninjas
rappelling in from the roof stuff - take it easy.' "

That is not news to Mr. Blaze, who said it was also a
familiar refrain in the world of computer security. "As any
computer security person knows," he said, "in a battle
between convenience and security, convenience has a way of


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