Think your cellphone call is private? Think again! GSM A5/1 encryption cracked.

Your cellphone calls aren't as secure and private as you might believe. The 2G GSM encryption standard A5/1 has been cracked, potentially exposing 80% of the world's calls to eavesdropping. In IT Blogwatch, bloggers listen in on this disturbing news.

By Richi Jennings. December 29, 2009.

Your humble blogwatcher selected these bloggy morsels for your enjoyment. Not to mention The many faces of a Space Invader...

    Kevin J. O’Brien divulges the news:

A German computer engineer ... has deciphered and published the secret code used to encrypt most of the world’s ... mobile phone calls. ... Karsten Nohl, aimed to question the effectiveness of the 21-year-old G.S.M. algorithm.


The G.S.M. Association ... called Mr. Nohl’s efforts illegal and said they overstated the security threat. ... Some security experts disagreed. ... About 3.5 billion of the world’s 4.3 billion wireless connections use G.S.M.; it is used by about 299 million consumers in North America.

Dan Goodin adds:

To capture both ends of a conversation, an attacker would have to place one of the radios in close proximity to the person making the call, while the second would be used to capture downlink transmissions coming from a carrier's base station. That requires a fair amount of effort [and] attackers must target a specific individual.


Nohl described the ... techniques at the 26th Chaos Communication Congress, an annual hacker conference in Berlin, along with fellow reverse engineer Chris Paget.

Karsten Nohl and Chris Paget monger fear:

The worlds most popular radio system has over 3 billion handsets in 212 countries and not even strong encryption. Perhaps due to cold-war era laws, GSM's security hasn't received the scrutiny it deserves. ... This bothered us enough to take a look; the results were surprising.


[It was] stunning to see what $1500 of [Universal Software Radio Peripheral] can do. Add a weak cipher trivially breakable after a few months of distributed table generation and you get the most widely deployed privacy threat on the planet. ... Prepare to change the way you look at your cell phone, forever.

Marc waves the flag:

GSM is the standard that is used for the AT&T and T-Mobile networks, and for the cellular networks of most of the rest of the world. It is used, not because it is technically superior, but because it is free to implement – no fees are necessary to use the microcode in chips of your own design.


As anyone slightly interested in this already knows, the chances of little Jimmie down the block listening to you talking to your mistress across the state and spilling the beans to your wife is not really applicable, but certainly the people who might be interested in more private things, say,  those from governments, are certainly able to do it. ... Still, just another small plus for the users of CDMA technology –  the Verizon and Sprint networks.

Marc Hav is dismissive:

I personally think this is yet another attention seeking article, this is nothing new, why else would the world leaders for years get special cellphones with 256-bit encryption or whatever if the existing technology is considered to be safe (until today as the article claims).

Kelly Hodgkins :

This is not the first time GSM was “cracked”. In 2003, the method by which GSM’s encryption code could be cracked was uncovered by a team of Israeli researchers and in 2008, David Hulton and Steve Muller presented at Black Hat a technique for the successful interception and decryption of a GSM stream using $1,000 of hardware and a half hour of time.


Before everybody panics, it is important to point out that the GSM algorithm that was cracked was the older and less secure 64-bit A5/1 algorithm, not the newer 128-bit A5/3 algorithm. Unfortunately, GSM carriers have been slow to adopt this new 128-bit encryption standard but Nohl’s disclosure may be the kick in the butt these lazy carriers need to beef up their security.

So what's your take?

Get involved: leave a comment.

    And finally...

Richi Jennings, your humble blogwatcher
  Richi Jennings is an independent analyst/consultant, specializing in blogging, email, and security. A cross-functional IT geek since 1985, he is also an analyst at Ferris Research. You can follow him as @richi on Twitter, or richij on FriendFeed, pretend to be richij's friend on Facebook, or just use good old email:

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