Gamified Intelligent Cyber Aptitude and Skills Training (GICAST)
Gamified Intelligent Cyber Aptitude and Skills Training (GICAST)

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

1.3 The key distribution problem

This section is part of the amber and green pathways.

Download this video clip.Video player: ou_futurelearn_cyber_security_vid_1019.mp4
Copy this transcript to the clipboard
Print this transcript
Show transcript|Hide transcript
 
Interactive feature not available in single page view (see it in standard view).

Traditionally, symmetric encryption suffered one enormous shortcoming – it was necessary for either the sender or the recipient to create a key and then send it to the other party. While the key was in transit, it could be stolen or copied by a third party who would then be able to decrypt any ciphertexts encrypted with that key.

Another problem is that large numbers of key pairs are needed between communicating parties. You would need one key each and two keys in all to communicate between you and another person (call them P1); three keys each between you, P1 and P2; six keys each between you, P1, P2 and P3; ten keys each between you, P1, P2, P3 and P4. This quickly becomes difficult to manage. This can be calculated as n(n-1)/2 where n is the number of communicating parties.

For example, if ten parties want to communicate with each other securely they would need 45 different key pairs: 10(10-1)/2 = 45. This would increase to 4,950 if there were 100 communicating parties!

This problem, called the key distribution problem, affected anyone wishing to use encryption until the 1970s, when a method of distributing keys without actually sending the keys themselves was developed independently by GCHQ in the United Kingdom and Whitfield Diffie and Martin Hellman in the United States. The British discovery was kept secret for many years, so today the solution is known as the Diffie–Hellman key exchange method.

Symmetric encryption methods have the advantage that encryption and decryption is extremely fast, making them ideal for transmitting large amounts of secure data. In the video you saw how key distribution was achieved between two people, Alice and Bob.

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371