Siemens GSM crypto-phone

The Crypto GSM is the first tap-proof mobile telephone on the market. The basis of the Crypto GSM is the renowed Siemens dualband mobile phone S35i. The core, however, is the crypto module which has been completely integrated into the S35i. Encrypted speech is transmitted on the transparent GSM data channel. To attain highest security, two algorithms are combined; an asymmetrical algorithm with a 1024-bit key for key agreement and a symmetrical algorithm with a 128-bit key for voice encryption. One touch of a key is all it takes to establish an encrypted connection. The caller merely has to dial the number of the desired subscriber and briefly press the crypto softkey below the display to switch to the crypto mode. Everything else is done automatically. A data call is initiated and within 15 seconds the key exchange will be performed. By pressing the End key, encrypted calls can be terminated in the same way as normal calls. As soon as the call ends the keys generated in the beginning are deleted. Besides the
long key this is one of the essential security features of the Crypto GSM.
Apart from encryption Crypto GSM optionally offers a further security function: the authentication. With a special software several Crypto GSM can be combined to closed user groups. An encrypted connection is only possible, if both partner devices belong to the same chosen user group.

Characteristics
The Crypto GSM is suitable for encrypted end-to-end voice communication in the GSM frequency ranges of 900 MHz and 1800 MHz. A confidential discussion can either be carried on between two Crypto GSM mobile phones. Or encrypted calls can be made from the Crypto GSM to the landlie network: the only prerequisite is that the called ISDN station must be protected by a Crypto 703+ of the Crypto product family. As a matter of course it is also possible to communicate with every subscriber in the normal unencrypted way.