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. Last Updated: 07/27/2016

Researchers Claim to Crack Wireless Phone Code

SAN FRANCISCO -- Two Israeli researchers say they have found an efficient way to crack the code that protects the privacy of conversations and data transmissions over a type of wireless telephone used by more than 215 million people worldwide.

The encryption method is part of the Groupe Speciale Mobile, or GSM, wireless phone standard. Though not dominant in the United States, it is the world's most widely used cellular technology. More than 215 million digital phones use it worldwide, including more than 100 million in Europe and 5 million in the United States.

Most cell phones in the United States are based on other wireless technologies, but several U.S. cellular phone companies, including Pacific Bell, a unit of SBC Communications Inc., and the Omnipoint Corp., use the GSM standard.

The code the researchers say they cracked is known as the A5/1 algorithm, which is supposed to protect calls from being intercepted by electronic eavesdroppers. It is not an authentication code, which prevents detecting a phone's number and "cloning" it in another phone to bill calls fraudulently.

While cell phone encryption has been cracked before, the new method is significant because it requires very little computer power; an eavesdropper with just a PC could break into a conversation in less than a second, its developers said.

Several methods of attacking the GSM algorithms have been announced before, but most were impractical, requiring several hours and a network of computers to intercept a single conversation.

The researchers who say they discovered the latest method are Alex Biryukov and Adi Shamir of the Weizmann Institute in Rehovot, Israel. The men said they were able to break the code using a computer with 128 megabytes of RAM and two 73 gigabyte hard disks. The computer is used to analyze the A5/1 algorithm in the first two minutes of the conversation, which is intercepted using a digital scanner. Once that data is gathered, the eavesdropper can listen to the entire conversation, they said.

For now, the new cracking method requires resources not available to most individuals. Before intercepting phone conversations, an eavesdropper must make one-time sophisticated computations that demand significant computer power. Once that is completed, though, all GSM-protected conversations are easily accessible, the researchers said.

An eavesdropper must also have access to a digital scanner, which can intercept wireless calls within a radius of several kilometers. Such devices cost thousands of dollars and are illegal in the United States.

Though the finding was not formally announced, it was confirmed on Monday by one of the researchers after word spread quickly among encryption experts on Internet mailing lists.

A spokesman for Omnipoint on Monday called the researchers' claims "ridiculous."

"What they're describing is an academic exercise that would never work in the real world," said the spokesman, Terry Phillips. "What's more, it doesn't take into account the fact that GSM calls shift frequency continually, so even if they broke into a call, a second later it would shift to another frequency, and they'd lose it."

But David Wagner, a computer security researcher at the University of California at Berkeley, insisted the discovery was significant.

"This is a big deal," he said. "I don't think that the frequency hopping will be a major barrier." He added that it put the interception of GSM calls "within the reach of corporate espionage."

Computer security researchers continually try to break codes because the measure of an encryption scheme is how much time and computing power are needed to crack it.

In 1998, Wagner and Ian Goldberg, also at Berkeley, and Marc Briceno of the Smart Card Developers Association demonstrated that they could crack an authentication method associated with GSM in a matter of hours on a single PC.

In their research, they found that the A5/1 algorithm used keys, which are used to scramble and unscramble the data, that were much shorter than advertised and thus much easier to break. That prompted speculation that the algorithm had been deliberately weakened to allow for government eavesdropping.

In August, Wagner, Goldberg and Briceno developed a method for breaking into calls protected by weak versions of the A5/1 algorithm used in parts of Asia and Australia.

Their method could break into a conversation in a fraction of a second with a single PC.