Pulling the requirements together

In the scenarios above, the requirements have built upon each other.

Service protection

If the connectivity is crucial to the mission, then sufficient security must be built into the system such that the probability of a denial of service attack being mounted and succeeding is less than or equal to the probability of connectivity being broken through faulty equipment or human error in configuration or maintenance.

Data Integrity

Obviously, if data can be removed, substituted or appended, then things can go wrong. For video and audio streams, the results could be anything from embarrassing through to disastrous - imagine insertion of manipulated images into a video stream to show someone with rabbit ears.

Authentication

It is often required that the sender of a stream must be authenticated, and additionally, the receivers of a stream must be authorised to view the media. This requires authentication.

Confidentiality

The stream should be protected from prying eyes, depending upon what is in the stream.

Key Distribution

Key distribution should be only to the authorised users, and on some occasions must scale both in the number of users and in the rate at which keys change.

Specialist requirements

There are many other security requirements depending upon particular circumstances, such as the ability to repudiate transmissions in the brain-storming scenario above. Other possibly requirements include the access control to the equipment in a video conference such as the cameras and microphones, and non-repudiation of transmission.

For the individual requirements, the best approach is to separate the actors within the application and construct their security requirements. However, in all cases, one must make the engineering trade-off of the cost of meeting the security requirement against the cost of not meeting the requirement and being insecure. There may be occasions when a different means of transmission, such as delivery by trusted human courier may be preferable.