Safe Outsourced Attribute-Based Signatures

Abstract

Furthermore, we apply this novel paradigm to existing ABS to reduce complexity and present two schemes, i) in the first OABS scheme, the number of exponentiations involving in signing is reduced from O(d) to O(1) (nearly three), where d is the upper bound of threshold value defined in the predicate; ii) our second scheme is built on Herranz et al's construction with constant-size signatures. The number of exponentiations in signing is reduced from O(d2) to O(d) and the communication overhead is O(1). Security analysis demonstrates that both OABS schemes are secure in terms of the unforgeability and attribute- signer privacy definitions specified in the proposed security model. Finally, to allow for high efficiency and exibility, we discuss extensions of OABS and show how to achieve accountability and outsourced verification as well.