Following the CCA conversions of Yamada et al. (PKC 2011, 2012) and Nandi et al. (ePrint Archive: 2015/457), one can have CCA-secure PE from CPA-secure PE if the primitive PE has either verifiability or delegation. We show that the fully secure CPA-construction of Attrapadung possesses the verifiability. The aforesaid approach degrades the performance of the resultant CCA-secure PE scheme. As an alternative, we provide a direct fully secure CCA-construction for PE from the pair encoding scheme. This costs an extra computation of group element in encryption and three extra pairing computations in decryption as compared to the CPA-construction of Attrapadung.
The predicate signcryption (PSC) is a super class of the existing class, the attribute-based signcryption (ABSC), where the confidentiality, unforgeability and signer privacy are well preserved. By combining the proposed frameworks for PS and PE, we provide a generic construction for PSC from the pair encodings. It achieves the perfect privacy, and the strong unforgeability and CCA security in the adaptive-predicates model. The construction has the support of combined-setup, where the distributions of public parameters and keys in the underlying signature and encryption schemes are identical. The proposed PSC provides many new results, e.g., the first PSC schemes for regular languages, the first ABSC with constant-size signcryptions and constant-size keys respectively, the unbounded ABSC with large universes in adaptive-predicates model, etc.Category / Keywords: public-key cryptography / Pair encodings, predicate encryption, predicate signature, predicate signcryption, attribute-based encryption, attribute-based signature, attribute-based signcryption, generic conversion Date: received 1 Oct 2015, last revised 18 Feb 2017 Contact author: tapasgmmath at gmail com Available format(s): PDF | BibTeX Citation Note: We correct some mistakes and typos. Version: 20170218:110057 (All versions of this report) Short URL: ia.cr/2015/955 Discussion forum: Show discussion | Start new discussion