Suppose that Sally (a server) needs access to a symmetric key for user Alice and

Question

Suppose that Sally (a server) needs access to a symmetric key for user Alice andanother symmetric key for Bob and another symmetric key for Charlie. Then Sallycould generate symmetric keys KA,KB, and KC and store these in a database. An alternative is key diversi?cation, where Sally generates and stores a singlekey KS . Then Sally generates the key KA when required as KA = h(Alice,KS ),with keys KB and KC generated in a similar manner. Describe one advantage andone disadvantage of key diversi?cation

Explanation / Answer

·         Using diversified keys to each user will help in privacy. Even if an attacker can know the key of one user, it will help in reading messages of only that user but not of any other.

·         Also using a single key KS will make the generation of keys easier.

Disadvantages:

·         With diversified keys, if somehow an attacker can obtain the key of a user, say Alice he can decrypt the diversified key KA as KS is known and as it is shared key.

·         There are chances for occurrence of errors while generating the key in a large number.

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