Another gem from the latest Der Spiegel NSA leaks: the NSA can listen in on all Skype traffic and read Skype messages, because Microsoft hands over its keys.
The nature of the Skype data collection was spelled out in an NSA document dated August 2012 entitled "User's Guide for PRISM Skype Collection." The document details how to "task" the capture of voice communications from Skype by NSA's NUCLEON system, which allows for text searches against captured voice communications. It also discusses how to find text chat and other data sent between clients in NSA's PINWALE "digital network intelligence" database.
The full capture of voice traffic began in February of 2011 for "Skype in" and "Skype out" calls—calls between a Skype user and a land line or cellphone through a gateway to the public switched telephone network (PSTN), captured through warranted taps into Microsoft's gateways. But in July of 2011, the NSA added the capability of capturing peer-to-peer Skype communications—meaning that the NSA gained the ability to capture peer-to-peer traffic and decrypt it using keys provided by Microsoft through the PRISM warrant request.
Newly published NSA documents show agency could grab all Skype traffic [Sean Gallagher/Ars Technica]