Cyber Security:

Symmetric Cryptography

Symmetric encryption suffers from one enormous security problem – it is 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 with symmetric cryptography is that a large number of key pairs are needed between communicating parties.

The more there are, the quicker it becomes difficult to manage.

If n is the number of connecting parties then the number of key pairs would be:

n(n-1)/2

For example, if ten parties want to communicate with each other securely they would need 45 different key pairs:

10(10-1)/2 = 10 x 9/2 = 90/2 = 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 see how key distribution is achieved between two people, Alice and Bob.