In GSM, each home network has an AuC database containing user keys Ki. Instead,

Question

In GSM, each home network has an AuC database containing user keys Ki. Instead, a process known as key diversification could be used. Key diversification works as follows. Let h be a secure cryptographic hash function and let Km be a master key known only to the AuCs. In GSM, each user has a unique ID known as an IMSI. In this key diversification scheme, a user's key Ki would be given by Ki = h(Km,IMSI), and this key would be stored on the mobile. Then given any IMSI, the AuC would compute the key as Ki = h(Km,IMSI).

a) What is the primary advantage of key diversification?
b) What is the primary disadvantage of key diversification?

Explanation / Answer

     In GSM, each home network has an AuC database containing user keys Ki. Instead, a process known as key diversification could be used. Key diversification can be used to eliminate such database requirement.

Technically sophisticated key management scheme employs different keys for each function, which is called key diversification. The key for each function is called the master key for that function. On the basis of this master key, individual keys can be derived for each smart card and supported function.

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