3.6 Key establishment
To communicate securely, Alice and Bob need to share the secret key in advance. According to [117], Def. 1.63, ”key establishment is any process whereby a shared secret key becomes available to two or more parties for subsequent cryptographic use”.
In principle, Alice and Bob might meet in person in a cafe and establish a shared secret. However, apart from the logistic problems, this approach does not scale very well: in a group of n people, each possible pair needs to establish a key of its own. As there are 
pairs, 100 people would need about 5,000 personal meetings. Obviously, an automated method of key establishment is in order.
Key establishment is a broad term in which we can further distinguish between key agreement and key transport. In a key agreement protocol, both parties involved have an influence on the final result, which is a shared key. The DH key exchange protocol mentioned in the first chapter is a prime example of a key agreement...
