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I read several papers about user revocation in IBE recently. A common point is that when a user is revoked, some other valid users should also update their private keys. Does this mean that one identity is actually associated with many users? If not, why do other valid users still need to update the keys?

I am also thinking whether the PKG can keep a list of revoked IDs. Then before sending out the message, the sender will check the list. If the ID is revoked, the sender can modify the public key as ID+ a random number. Then the receiver can update the private key according to the new public key. What's the problem with this idea? Does it violate the design philosophy of IBE?

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  • $\begingroup$ I think I can update the question myself now. The state of the art requires that the sender encrypts the message using <ID||current time> as the public key. For example, the time may be divided into weeks. So a sender may encrypt using <Bob||week 1> and then <Bob||week 2>. Since the public key changes with time, all receivers have to update their secret key from time to time. The papers I read then try to reduce the number of users that need to update the keys. Still, I have the question described in the second paragraph above. $\endgroup$ – Paradox Nov 29 '15 at 0:55

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