Secure Push-To-Talk (PTT) - Encryption and Server Specifications

Secure Push-To-Talk Technology

Secure PTT is integration of (police) radio  into standard mobile phones.  PoC solution on mobile  phones combines all features of encrypted PMR with the added benefits of much better audio quality, distance-independent national/international group coverage and completely covert (undercover) appearance.

Secure PTT Software is designed as a secure replacement of the radio equipment which police and security forces are using nowadays. Additionally, the lists of currently connected people are instantly available, as well as private one-to-one secured talks with selected members of the group.

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General brochure (A3)

Nabishi Secure PTT Encryption System

Secure PTT Server and configuration

1. Secure PTT is client-server application. Secure PTT Server is server software deployed on a Linux server that has Internet connection. Secure PTT Server contains all information about the channel structure and mobile clients that are authorized to connect to the channels. Secure PTT Server is designed to work 24/7 and has a built-in clustering technology to provide fail over solution.

2. Secure PTT mobile client is installed on the mobile devices. Once started Secure PTT client is connected to the Secure PTT Server.  Target devices are Nokia Series 60.3 smart phones.

3. The connection from client to server is made using Internet channel. We have successful experience using solution with EDGE, 3G and Wi-Fi type of connection.  The desired Access Point can be defined in settings of the Secure PTT client.

4. Secure PTT client operates either directly with mobile device or via compatible headset. There is a special support for Vigilite headset that is in used by some police forces. Support of other special headset can be added on request.

Workflow and Security algorithm

Secure PTT solution has next data security algorithm and workflow:

1. After Connection to the server is an authorization take place. Secure PTT Server decides based on the credentials sent from the mobile if mobile client is authorized to use the system and what channels are available. Currently information about mobile clients that are eligible using this Secure PTT Server should be stored in the server database BEFORE a client can successfully connect.

2. Encryption session is initiated. Client and server are using Diffie Hellmann 4096 to exchange keys. When keys are exchanged all data are encrypted by using AES 256.

3. Mobile clients select channel from the available list. User can select channel manually in Secure PTT client. If channel selection is successful user hears welcome note with channel name e.g. “channel two”

4. To initiate voice transmission user is Pushing and holding push-to-talk button on headset or on the mobile device (PTT button). While user is Pushing PTT button the voice data is recorded, encoded with AMR codec, encrypted with AES 256 and sent to Secure PTT Server. If user will Push the PTT button when other party is already speaking on the channel he will hear “blocking” beep as only one person is allowed to speak on the channel.

5. Secure PTT Server receives encrypted data and dispatches it to all other parties on the channel.

6. When user releases the button then the transmission is finished. 

7. All other parties on the channel receive encrypted data from the Secure PTT Server. Then data is decrypted with AES 256 with keys previously received by using Diffie Hellmann 4096. Audio is being played to the either headset or loudspeaker of the mobile device.

8. All the time Secure PTT client is checking if connection with server is still active. If it is interrupted e.g. there is no Internet coverage then Secure PTT client tries to reconnect automatically.

9. In case of connection lost an attempt to reconnect takes place.

10. For secure one-to-one talk a private channel is created, available only for two persons involved.

11. There is also sound and popup notification of the incoming one-to-one talk request.

Compatible devices

Nokia Series 60.3 FP1 and FP2: supported
Nokia Series 60.5: supported

See list of Compatible Nokia Phones

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