NSA can decode many GSM cellphone calls
The NSA may say that its phone surveillance efforts focus on metadata rather than the associated calls, but we now know that the agency can listen to many of those conversations whenever it wants. Documents leaked to the Washington Post by Edward Snowden confirm that the NSA can decode GSM-based cellphone calls without obtaining the encryption keys. The ability isn’t surprising when GSM has known weaknesses, but the document suggests that the NSA (and potentially other US agencies) can easily process cellphone calls worldwide. Not surprisingly, the intelligence branch argues that such cracking is necessary — folks on both sides of the law use encryption to hide information, after all. The NSA may not have such an easy time in the future, however. AT&T, T-Mobile Germany and other carriers worldwide are moving to tougher encryption methods for their GSM service, and 3G calls are typically more secure as a matter of course. These measures don’t prevent eavesdropping, but they do complicate any attempts to snoop on cellular chats.
Source: Washington Post