Efficient Two-Move Blind Signatures in the Common Reference String Model

Blind signatures provide a mechanism for achieving privacy and anonymity whereby a user gets the signer to sign a message of his choice without the signer learning the content of the message, nor linking message/signature request pairs when he sees the final signature. In this paper, we construct a blind signature that requires minimal interaction (two moves) between the user and the signer, and which results in a signature which is a signature with respect to a standard (i.e. non-blind) signature scheme. The signature request protocol is akin to the classic, blind-unblind methodology used for RSA blind signatures in the random oracle model; whilst the output signature is a standard CamenischLysyanskaya signature in bilinear groups. The scheme is secure in the common reference string model, assuming a discrete logarithm related assumption in bilinear groups; namely a new variant of the LRSW assumption. We provide evidence for the hardness of our new variant of the LRSW by showing it is intractable in the generic group model.