Assuming each of the N people has his/her own Computer; n (n-1) numbers of keys are required to ensure a secure communication between the people in the organization. This is because each computer requires a secret key that it uses to encrypt a packet of information before it is sent over the network to the second computer. The second computer requires the same secret key used by the sending computer to decrypt the received message. Each person in the organization requires n-1 number of keys to communicate securely with the rest of the people in the organization. Since there are N people in the organization, n (n-1) numbers of keys will be required. Symmetric key requires that each person should know which computers he/she will be communicating with so that one can install the key on each one (American Library Association 2002).
The number of keys required for a public key encryption
In the case of public key encryption, 2n number of keys will be required to ensure a secure communication. This is because public key encryption uses two different keys at once; a combination of a public key and a private key. Private Key will only be known to the sender computer, and the public key will be given by the sender computer only to the receiver computer (Boyer 1990, 24). To decode the encrypted message, the receiver computer must use the public key, provided by the originating computer, and its own private key. Since there are N people in the organization, and each person requires 2 key to securely communicate with each other, 2n will be the number of key required for a secure communication in the organization (Kurose).
Using Alice public key and his private key Bob decrypt and recovers the message Ks sent by Alice. He then uses keys to remove the digital signature inserted by Alice. Bob then uses his private key to decode and read the message sent by Alice.
Advantages of using a Key Distribution Centre (KDC) in an organization
Key Distribution Centre helps in protecting organization against password sniffing, database stealing, and maintenance of huge number of account databases (Duderstadt 2000, 15). It precludes plaintext passwords from being channeled over the electronic network. KDC centralizes organization employee usernames and password information and, therefore, make it easier for the organization to manage and maintain the data (Smith 2000). Also, it prevents storage of password information locally and, therefore reduces the chances of compromising the single machine.
Checking whether KDC is live
Alice should request for authentication to be sent to the workhorse of the KDC generator. She should then wait for an encrypted ticket granting ticket which contains the session key. Using secret key, she should successfully decrypt the ticket granting ticket which will present to her an enclosed session key to a ticket granting service (Eaton 2000). The ticket granting service will issue her a ticket which will provide her with the authentication she needs to use the service. Alice can only decrypt the encrypted ticket only if she knows the secret key and, therefore, a secure authentication will take place. There is timestamp information included in the ticket that prevents replay attacks and, therefore the message Alice receives will not be a playback attack.