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Posted at 7:17 a.m. PDT Monday, April 13, 1998

Code cracked on a digital cellular phone



SAN FRANCISCO -- Cryptographers have ``cloned'' a digital cellular phone -- until now considered impossible.

Cloning, or copying the codes in a cell phone so that an unauthorized user can use them to make calls on another phone, costs the industry millions of dollars every year. Thieves use specially configured analog cell phones to steal codes out of the airwaves, then sell cheap, illegal calls.

Advertising for digital cell phones has focused on their security, which is stronger than analog phones.

Still growing in the United States, digital phones are booming internationally. The Global System for Mobile Communications (GSM) digital standard is the most widely used in the world, with more than 79 million phones in use. The cryptographers used a GSM phone -- relatively rare in the United States.

The cryptographers' recent feat, announced Saturday, is the first public cracking of any digital phone code. ``As to the public at large, caveat emptor (let the buyer beware),'' said David Wagner, who with fellow University of California-Berkeley graduate student Ian Goldberg broke the encryption algorithm in ``about five hours.''

Encryption uses an algorithm to scramble data to make them secure. Fellow researcher Marc Briceno of the Smartcard Developers Association provided the digital phone's algorithm after two months of tinkering with the phone's chip on nights and weekends, he said, with only ``a home-built smart card reader and a laptop.''

The trio did the research purely as a challenge. Wagner and Goldberg also found a security flaw in Netscape's Web browser in 1995 and broke analog phone codes last year.

Among cryptographers, a code isn't considered fully tested unless everyone's had a crack at it. Strong encryption withstands all but the most determined, time-consuming attacks.

One reason they wanted to test the chip's code was that it was designed in secret. ``Security through obscurity doesn't work,'' said Wagner, who urged the industry to make security designs public -- as many code creators do -- so cryptographers can test them.

In the meantime, digital phone owners need not panic or turn in their phones, Wagner said. ``If anyone should be concerned, it should be the network services,'' he said.

To clone a GSM phone, hackers would need to have it for six to eight hours to extract the code key from the chip inside the phone. That single copy wouldn't be of much use because digital networks don't allow the same account to be used by more than one phone at a time, notes GSM operators alliance spokesman George Schmitt of Omnipoint Communications, Cedar Knolls, N.J.

Schmitt applauds the accomplishment but said he slept like a baby despite the news. ``If I'd thought it was a real problem ... I wouldn't have.''

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