Universally Composable Blind Signatures in the Plain Model

In the universal composability framework, we define an ideal functionality for blind signatures, as an alternative to a functionality recently proposed by Fischlin. Fischlin proves that his functionality cannot be realized in the plain model, but this result does not apply to our functionality. We show that our functionality is realized in the plain model by a blind signature protocol if and only if the corresponding blind signature scheme is secure with respect to blindness and non-forgeability, as defined by Juels, Luby and Ostrovsky.