Why Secure?

  GSM Security

  Fixed Line Security

  FAQ's about Encyrption

FREQUENTLY ASKED QUESTIONS

How do I make an encrypted call ?

On the Sec-Tel  phone  there are two buttons which are used to make a call.    The ‘green’ button is used to initiate normal calls and to answer all incoming calls.   The ‘Crypto-button’ is used to make crypto calls.

What happens when I press the encrypt-button ?

After entering the phone number and pressing the crypto-button, the mobile phone will establish a link to the other party using a GSM data channel (similar to a fax call).

The Sec-Tel  on the other side will ring with a distinctive ringtone, and show “Crypto incoming” on the display.    When the call is answered, a number of initial checks are done internally in order to validate the system and keys of both phones.   These checks include ensuring the integrity of the other party’s key by validating the digital signature which was issued by the Certification Authority and validating any restrictions such as Black Lists, White lists etc.

If the checks are successful then a session key is generated, encrypted and signed using public key algorithms, before being transmitted.   The use of public key algorithms during key exchange ensures that only the intended Sec-Tel phone  is capable of deciphering the information.   If any of these checks fail, the call is halted and an appropriate message displayed.

During the key exchange process, which lasts about 7 seconds, progress tones can be heard in the earpiece of both phones, serving as a reminder that a secure call is being established.

 The randomly generated session key will be used to initiate the voice ciphering process and the conversation can commence.   From here on, both cell phones will encrypt all speech before transmission, rendering the call secure in both directions.

At the end of the call, the session key is securely discarded and never used again and all power is removed from the crypto module, which further ensures that all data related to the call is destroyed.

How is the quality of encrypted calls ?

The additional compression method used in encrypting calls is more modern than that used for GSM, although there is additional bandwidth overhead required for such a call.    Sound quality is the same as a normal voice call.   There is a fractional increase in latency (delay) of about half a second, which is hardly noticeable and does not affect the conversation.

In unfavourable reception conditions, problems may occur in the same way as with other mobile phone calls.   However, in the case of a fast car ride, secure calls may break off more often than when stationery because the data channel requires a higher stability in the connection.