It is estimated that, in most countries where mobile communications are available, the volume of mobile communication traffic now equals the volume in fixed networks. As mobile traffic continues to increase, the use of fixed services is likely to become the exception rather than the rule.
The same security risks that plague fixed-line telephone network are also evident in mobile (ie GSM cellular and satellite) networks. Although the over-the-air link between a GSM handset and the base station is encrypted, the fixed network interconnecting the base stations is the same as that of the fixed-line telephone network.
Nanoteq has developed the CodeVoice Mobile, a voice encryption unit for mobile communications which can be used to encrypt voice for transmission via Inmarsat satellite networks, GSM (and other cellular) networks and the fixed-line Public Switched Telephone Network (PSTN). It can therefore be used to communicate between mobile and fixed line networks.
Nanoteq director Mike Venter explains the default symmetric encryption algorithm used is an International Data Encryption Algorithm (IDEA), with a key length of 128-bits. A 1024-bit RSA-based Diffie-Hellman protocol is used to authenticate the remote user and to exchange the session keys between connected units.
"Security is achieved by converting the analogue voice signal into low bit rate data, through voice compression techniques, which is encrypted before it is transferred via the mobile or satellite network. Even if the encrypted data is intercepted, it is impossible to recover the original unencrypted data and therefore the original analogue voice without the cryptographic keys," he notes.
The two important elements are therefore the voice compression and the encryption. The voice compression must offer near-phone quality and caller recognition while the encryption must be standards-based and have a symmetric key length of at least 128-bits.
Venter says that with satellite communication there are even more security risks. The over-the-air link is not encrypted and due to the nature of satellite communications, they can be intercepted from anywhere within the communication footprint of the satellite. For example, some types of satellite communication can be intercepted with readily available off-the-shelf equipment.
To communicate via the Inmarsat satellite network, the CodeVoice Mobile unit is connected to an Inmarsat Mini-M terminal (satellite phone), via a serial cable. The compressed and encrypted voice is transferred via the 2.4kbps data channel of the satellite phone system, to the remote CodeVoice unit. In order to compress the analogue voice signal to fit the 2.4kbps satellite phone data channel, the CodeVoice range uses a proprietary specialised vocoder that offers near-phone quality and caller recognition.
The remote unit can be one of the following:
* CodeVoice Mobile connected to a Mini-M terminal
* CodeVoice Mobile fitted with a PCMCIA modem (connected either to the PSTN or a GSM handset)
* CodeVoice Mobile fitted with a PCMCIA GSM radio modem such as the Nokia Cardphone 2.0
* CodeVoice PSTN connected to the analogue telephone network
* CodeVoice PSTN connected to a Mini-M terminal
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