GCHQ & NSA hacked the worlds largest SIM manufacturer Gemalto to get keys to decrypt calls according to Edward Snowden.
http://www.theregister.co.uk/2015/02...ys_to_kingdom/
Quote:
“The target for the team was the unique Ki encryption keys baked into each of Gemalto's SIM cards. These 128-bit values are hidden away inside the SIM electronics, and are supposed to be kept secret. Every SIM has one, regardless of its manufacturer.
Mobile networks keep a copy of a SIM's Ki key before the card is given to a subscriber. This is so that the carrier can identify and authenticate the device containing the SIM when it joins a network.”
“The target for the team was the unique Ki encryption keys baked into each of Gemalto's SIM cards. These 128-bit values are hidden away inside the SIM electronics, and are supposed to be kept secret. Every SIM has one, regardless of its manufacturer.
Mobile networks keep a copy of a SIM's Ki key before the card is given to a subscriber. This is so that the carrier can identify and authenticate the device containing the SIM when it joins a network.”
http://www.theregister.co.uk/2015/02...ys_to_kingdom/