Efficient Attribute-based Signcryption Systems with Anonymity

In this paper, we propose two ciphertext-policy attribute-based signcryption (CP-ABSC) schemes which are efficient and fully secure. These systems are BasicABSC and AnonABSC. In addition to providing confidentiality, unforgeability and access control to the signcrypted data, the presented AnonABSC scheme is anonymous. i.e. an opponent can not decide for which policies or attributes the data is signcrypted. This is very useful especially when the signcrypted data are stored in a public cloud on the Internet. Seemingly, this is the first CP-ABSC which attains such property. In addition, The proposed systems are time- and power-efficient and they do not depend on expensive paring operations which make them suitable for mobile and lightweight devices. The proposed systems are completely protected using the quadratic residuosity Q notion and offer a constant ciphertext length irrespective to the amount of attributes related to the access structure.