This question is from Computer Network Security, (Applied Cryptography) Imagine

Question

This question is from Computer Network Security, (Applied Cryptography)

Imagine a peer-to-peer network where 1000 users want to communicate in an authenticated and confidential way without a central Trusted 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 Center, KDC)? What is the main advantage of a KDC against the scenario without a KDC? How many keys are necessary if we make use of asymmetric algorithms? Also differentiate between keys which every user has to store and keys which are collectively necessary.

Explanation / Answer

1)
In symmetric algorithms both sender and reciever shares same key. If any one knows the
secret key , they can decrypt the message.
So as 1000 users users are there.... that is 500 pairs.
So 500 keys required.

------------------------------------------------------------------------------
2)
KDC will take request from user to use some service. So KDC using some cryptographic
techniques, it will authenticate the requesting users or other parties who were
trying to access this service or message.
So it will involves mainly with symmetric notation. So it will deals with sending
secret key along with KDC ticket.
So keys numbers will change. It is required 500 keys +500 KDC tickets so 1000 keys as explained in 1st answer.

---------------------------------------------------------------------------------
3)

As already explained in first answer, in syymetric algoritm techniques, the data can be
accessed using key which was shared by both same key. So there will not be complete
security. If any one knows that secrey key, then message can be read/tampered by
any one.

So to avoid this KDC was placed. It additionally encrypted message using some ticket
(also called to be key). So this key will be shared to other user only after reaching
messgae. So using this token, the user will decrypt and can able to read message.

--------------------------------------------------------------------------------------
4)
Assymetric algorithm will use pair of keys. As 500 pairs are there. so 500x2 = 1000 keys required.

Sender will encrypt the message using public key and reciever has to be decrypt the message
using private key or secret key.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.