Anonymous spatial encryption under affine space delegation functionality with full security

Anonymous encryption provides the decrypter's identity privacy preservation as well as plaintext confidentiality. Spatial encryption, which is a kind of functional encryption, provides a generalized framework for special property encryption schemes such as broadcast encryption, predicate encryption, forward secure encryption, (hierarchical) identity-based encryption, delegatable attribute-based encryption etc. In this paper, we propose an anonymous spatial encryption scheme that deploys an affine subspace delegation mechanism. Our proposed scheme captures the message confidentiality, recipient anonymity, adaptive security, partial-order delegation and short ciphertext, simultaneously. To the best of our knowledge, the proposed scheme is the first anonymous spatial encryption that provides the anonymity property in adaptive security model, whose construction is based on a dual system encryption mechanism in bilinear composite-order groups. We also give a conversion construction to move into a prime-order setting with canceling property, whose security is based on the Decision Linear Problem. Finally, we provide a transformation methodology to obtain a CCA-secure scheme that combines a one-time signature, delegation functionality and the CPA-secure scheme.