Imagine a peer-to-peer network where 1000 users want to communicate in an authen
ID: 3768126 • Letter: I
Question
Imagine a peer-to-peer network where 1000 users want to communicate in an authenticated and confidential way without a centralTtrusted Third Party (TTP). How many keys are collectively needed, if symmetric algorithms are deployed? How are these numbers changed, if we bring in a central instance (Key Distribution Centre, KDC)? What is the main advantage of a KDV against the scenario without a KDC? How many keys are necessary if we make use of asymetric algorithms? Also differentiate between keys which every user ha to store and keys which are collectively necessary.Explanation / Answer
1) If symmetric algorithms are deployed then number of keys needed=(n*(n-1))/2 =((1000*999)/2)=499500.
where n is number of users.
2) A secret key is established between KDC and each user.
If KDC is not used then number of keys is of O(n^2).
If KDC is used then number of keys is of O(n).
3) The main advantage of KDC : number of keys generated are greatly reduced and also reduce the risks inherent in exchanging keys.
4) If we use assymetric algorithms number of keys required are 2*n=2*1000=2000 keys.
2 for each user.
one is a public key which is know to other users and a secret key which only user knows about it.