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equipment prices within reach of many experimenters. Already we have seen the
appearance of first-generation cellular phones on the used market, and new
units can be purchased for well under $1000 in many markets.
How High The Loss?
Subscribers who incur fraudulent charges on their bills certainly can't be
expected to pay them. How much will fraud cost the carrier? If the charge is
for home-system airtime only, the marginal cost to the carrier of providing
that service is not as high as if toll charges are involved. In the case of
toll charges, the carrier suffers a direct cash loss. The situation is at its
worst when the spoofer pretends to be a roaming user. Most inter-carrier
roaming agreements to date make the user's home carrier (real or spoofed)
responsible for charges, who would then be out hard cash for toll and airtime
charges.
We have not attempted to predict the dollar losses this chicanery might
generate because there isn't enough factual information information for anyone
to guess responsibly. Examination of current estimates of long-distance-toll
fraud should convince the skeptic.
Solutions
The problems we have described are basically of two types. First, the ESN
circuitry in most current mobiles is not tamper-resistant, much less
tamper-proof. Second and more importantly, the determined perpetrator has
complete access to all information necessary for spoofing by listening to the
radio emissions from valid mobiles because the identification information
(ESN/MIN) is not encrypted and remains the same with each transmission.
Manufacturers can mitigate the first problem by constructing mobiles that more
realistically conform to the EIA requirements quoted above. The second
problem is not beyond solution with current technology, either. Well-known
encryption techniques would allow mobiles to identify themselves to the
serving cellular system without transmitting the same digital bit stream each
time. Under this arrangement, an interloper receiving one transmission could
not just retransmit the same pattern and have it work a second time.
An ancillary benefit of encryption is that it would reasonably protect
communications intelligence--the digital portion of each transaction that
identifies who is calling whom when.
The drawback to any such solution is that it requires some re-engineering in
the Mobile-Land Station Compatibility Specification, and thus new software or
hardware for both mobiles and base stations. The complex logistics of
establishing a new standard, implementing it, and retrofitting as much of the
current hardware as possible certainly presents a tough obstacle, complicated
by the need to continue supporting the non-encrypted protocol during a
transition period, possibly forever.
The necessity of solving the problem will, however, become apparent. While we
presently know of no documented cases of cellular fraud, the vulnerability of
the current standards and experience with similar technologies lead us to
conclude that it is inevitable. Failure to take decisive steps promptly will
expose the industry to a far more expensive dilemma. XXX
Geoffrey S. Goodfellow is a member of the senior research staff in the
Computer Science Laboratory at SRI International, 333 Ravenswood Ave., Menlo
Park, CA 94025, 415/859-3098. He is a specialist in computer security and
networking technology and is an active participant in cellular industry
standardization activities. He has provided Congressional testimony on
telecommunications security and privacy issues and has co-authored a book on
the computer 'hacking' culture.
Robert N. Jesse (2221 Saint Paul St., Baltimore, MD 21218, 301/243-8133) is an
independent consultant with expertise in security and privacy, computer
operating systems, telecommunications and technology management. He is an
active participant in cellular standardization efforts. He was previously a
member of the senior staff at The Johns Hopkins University, after he obtained
his BES/EE from Johns Hopkins.
Andrew H. Lamothe, Jr. is executive vice-president of engineering at Cellular
Radio Corporation, 8619 Westwood Center Dr., Vienna, VA 22180, 703/893-2680.
He has played a leading role internationally in cellular technology
development. He was with Motorola for 10 years prior to joining American
TeleServices, where he designed and engineered the Baltimore/Washington market
trial system now operated by Cellular One.
--------
A later note indicates that one carrier may be losing something like $180K per
month....
==Phrack Inc.==
Volume Two, Issue 12, Phile #1 of 11
Index
~~~~~
3/29/87
Ok, so we made it through another few delayed weeks of saying a
release was coming soon. But of course, I finally got motivated and got this
issue moving. I'd like to thank many of the people who rushed themselves to
get their articles to me when they didn't know that the release was so soon,
and for those that haven't gotten their articles in in time (for two issues,
mind you [no names mentioned, of course, but I felt a denotation would be
sufficient to provide my feelings in the introduction]) a big, "Oh well."
We're glad you've continued your patronage (Ha!) with Phrack Inc. over the