Cloud-aided attribute-based encryption with efficient tracing and accountability auditing

Abstract

How to ensure data confidentiality and prevent data abuse has been a major challenge of cloud storage services. Attribute-based encryption (ABE) provides a solution for this problem by allowing authorized users with proper attributes to decrypt the ciphertext. Traceability and accountability are indispensable requirements for an ABE system to trace users leaking their private keys and to audit the accountability of authority in framing innocent users. However, in existing related works, user has a typically large private key, the size of which depends on the number of user’s attributes. Accordingly, the tracing and auditing costs are computationally expensive. To alleviate the cost of tracing and auditing, we construct a cloud-aided ABE scheme with efficient tracing and auditing. Specifically, we replace the ABE-type private key in previous works by the “transform key”. Given an ABE ciphertext, if the user is authorized to decrypt it, the cloud could use the transform key to transform the ABE ciphertext to a simpler one related to user’s identity. In this case, the user only needs to keep a fairly short and constant-size private key. As a result, it is much more efficient to trace and audit such a short private key in our scheme.