efficient revocation and threshold pairing based cryptosystems
Boneh, Ding, Tsudik and Wong recently proposed a way for obtaining fast revocation of RSA keys. Their method consists in using security mediators that keep a piece of each user's private key in such a way that every decrytion or signature operation requires the help of the mediator for the user. Revocation is achieved by instructing the mediator to stop helping the user to sign or decrypt messages. This security architecture, called SEM, gave rise to an identity based mediated RSA scheme (IB-mRSA) that combines the advantages of fast revocation and identity based public keys. We show that, in opposition to what was stated in [9], this revocation method can be applied to several existing public key encryption and signature schemes (all those for which a secure practical threshold adaptation exists) including the Boneh-Franklin identity based encryption scheme and a pairing based digital signature schemes. We first describe a threshold adaptation of the Boneh-Franklin identity based encryption scheme and, then, we compare the mediated versions of these schemes with IB-mRSA from security and efficiency points of view.
revocation public key cryptosystems bilinear maps