CryptoPhone mobile phones run on top of a heavily modified and stripped-down Microsoft Windows Mobile. Windows Mobile provides an affordable and well-researched platform that offers ample performance for the speech encoding and crypto functions. A Windows Mobile based system was chosen as the first CryptoPhone platform because it was the only sufficiently fast device allowed us to do software integrity protection in ROM and the stripping of unnecessary functions.
We are continiously evaluating other platforms for CryptoPhone products and will put up announcements of additional platforms in due time. Unfortunately there is at this point in time no viable mass-market Linux based phone with sufficient choice of device form factors, performance, stability, hardware integration and availability on the market, as we of course would prefer a completely auditable source base for our products.
We are aware that there are risks associated with using any Windows platform and we have taken a number of extensive measures to mitigate these risks as best as we could. We removed applications, communication stacks and system parts that are unnecessary for the CryptoPhone’s operation and which may cause potential security problems. Since we introduced our operating system hardening in 2003, for every attack that was published against Windows Mobile since then we could show that we had already identified the threat and disabled the affected components years before in CryptoPhones. While this is no guarantee for the future, we have at least a provable continuous track record in respect to systematically securing mobile devices, which is much more than our competition has to show.
Most important for you as a user is that you should not install third party software on the CryptoPhone to prevent software based attacks on the firmware integrity. Protection against trojaned software that is intentionally installed by the user is nearly impossible, so it is your responsibility as a user to prevent that risk by not installing untrusted software on your device. The CryptoPhone firmware update mechanism is cryptographically secured.
The diagram below provides a schematic overview of the software architecture of GSMK CryptoPhones for your reference.