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older systems.
First, the number of subscribers that older systems could support fell far
short of the demand in some areas, leading groups of users to share a single
mobile number (fraudulently) by setting several phones to send the same
identification. Carriers lost individual user accountability and their means
of predicting and controlling traffic on their systems.
Second, systems had no way of automatically detecting use of stolen equipment
because thieves could easily change the transmitted identification.
In theory, the required properties of the ESN allow cellular systems to check
to ensure that only the correctly registered unit uses a particular MIN, and
the ESNs of stolen units can be permanently denied service ('hot-listed').
This measure is an improvement over the older systems, but vulnerabilities
remain.
Ease of ESN Tampering
Although the concept of the unalterable ESN is laudable in theory, weaknesses
are apparent in practice. Many cellular phones are not constructed so that
'attempts to change the serial number circuitry renders the mobile station
inoperative.' We have personally witnessed the trivial swapping of one ESN
chip for another in a unit that functioned flawlessly after the switch was
made.
Where can ESN chips be obtained to perform such a swap? We know of one recent
case in the Washington, D.C. area in which an ESN was 'bought' from a local
service shop employee in exchange for one-half gram of cocaine. Making the
matter simpler, most manufacturers are using industry standard Read-Only
Memory (ROM) chips for their ESNs, which are easily bought and programmed or
copied.
Similarly, in the spirit of research, a west coast cellular carrier copied the
ESN from one manufacturer's unit to another one of the same type and
model--thus creating two units with the exact same identity.
The ESN Bulletin Board
For many phones, ESN chips are easy to obtain, program, and install. How does
a potential bootlegger know which numbers to use? Remember that to obtain
service from a system, a cellular unit must transmit a valid MIN (telephone
number) and (usually) the corresponding serial number stored in the cellular
switch's database.
With the right equipment, the ESN/MIN pair can be read right off the air
because the mobile transmits it each time it originates a call. Service shops
can capture this information using test gear that automatically receives and
decodes the reverse, or mobile-to-base, channels.
Service shops keep ESN/MIN records on file for units they have sold or
serviced, and the carriers also have these data on all of their subscribers.
Unscrupulous employees could compromise the security of their customers'
telephones.
In many ways, we predict that 'trade' in compromised ESN/MIN pairs will
resemble what currently transpires in the long distance telephone business
with AT&T credit card numbers and alternate long-distance carrier (such as
MCI, Sprint and Alltel) account codes. Code numbers are swapped among
friends, published on computer 'bulletin boards' and trafficked by career
criminal enterprises.
Users whose accounts are being defrauded might--or might not--eventually
notice higher-than-expected bills and be reassigned new numbers when they
complain to the carrier. Just as in the long distance business, however, this
number 'turnover' (deactivation) won't happen quickly enough to make abuse
unprofitable. Catching pirates in the act will be even tougher than it is in
the wireline telephone industry because of the inherent mobility of mobile
radio.
Automating Fraud
Computer hobbyists and electronics enthusiasts are clever people. Why should
a cellular service thief 'burn ROMs' and muck with hardware just to install
new IDs in his radio? No Herculean technology is required to 'hack' a phone
to allow ESN/MIN programming from a keyboard, much like the IMTS phone thumb
wheel switches described above.
Those not so technically inclined may be able to turn to mail-order
entrepreneurs who will offer modification kits for cellular fraud, much as
some now sell telephone toll fraud equipment and pay-TV decoders.
At least one manufacturer is already offering units with keyboard-programmable
MINs. While intended only for the convenience of dealers and service shops,
and thus not described in customer documentation, knowledgeable and/or
determined end users will likely learn the incantations required to operate
the feature. Of course this does not permit ESN modification, but easy MIN
reprogrammability alone creates a tremendous liability in today's roaming
environment.
The Rolls Royce of this iniquitous pastime might be a 'Cellular Cache-Box.' It
would monitor reverse setup channels and snarf ESN/MIN pairs off the air,
keeping a list in memory. Its owner could place calls as on any other
cellphone. The Cache-Box would automatically select an ESN/MIN pair from its
catalog, use it once and then discard it, thus distributing its fraud over
many accounts. Neither customer nor service provider is likely to detect the
abuse, much less catch the perpetrator.
As the history of the computer industry shows, it is not far-fetched to
predict explosive growth in telecommunications and cellular that will bring