Publicly Verifiable Outsourcing Computation for QR Decomposition Based on Blockchain

In the Big Data Era, outsourcing computation has become increasingly significant as it supplies computation resources for clients with limited resources. However, there are still many security challenges such as payment fairness, privacy protection, and verification. In this paper, we propose a secure publicly verifiable outsourcing computation scheme for the large-scale matrix QR decomposition. In the proposed scheme, client can pay for outsourcing services through blockchain-based payment system which achieves the payment fairness. Moreover, to protect privacy, both permutation matrix and block diagonal matrix are applied in encryption process. Meanwhile, to achieve the public verification, the computational complexity is reduced by using the matrix digest technology. It is worth mentioning that our scheme is provable and secure under the co-CDH assumption.

Revocable Identity-Based Encryption and Server-Aided Revocable IBE from the Computational Diffie-Hellman Assumption

An Identity-based encryption (IBE) simplifies key management by taking users’ identities as public keys. However, how to dynamically revoke users in an IBE scheme is not a trivial problem. To solve this problem, IBE scheme with revocation (namely revocable IBE scheme) has been proposed. Apart from those lattice-based IBE, most of the existing schemes are based on decisional assumptions over pairing-groups. In this paper, we propose a revocable IBE scheme based on a weaker assumption, namely Computational Diffie-Hellman (CDH) assumption over non-pairing groups. Our revocable IBE scheme is inspired by the IBE scheme proposed by Döttling and Garg in Crypto2017. Like Döttling and Garg’s IBE scheme, the key authority maintains a complete binary tree where every user is assigned to a leaf node. To adapt such an IBE scheme to a revocable IBE, we update the nodes along the paths of the revoked users in each time slot. Upon this updating, all revoked users are forced to be equipped with new encryption keys but without decryption keys, thus they are unable to perform decryption any more. We prove that our revocable IBE is adaptive IND-ID-CPA secure in the standard model. Our scheme serves as the first revocable IBE scheme from the CDH assumption. Moreover, we extend our scheme to support Decryption Key Exposure Resistance (DKER) and also propose a server-aided revocable IBE to decrease the decryption workload of the receiver. In our schemes, the size of updating key in each time slot is only related to the number of newly revoked users in the past time slot.

Certificateless Key-Insulated Generalized Signcryption Scheme without Bilinear Pairings

Generalized signcryption (GSC) can be applied as an encryption scheme, a signature scheme, or a signcryption scheme with only one algorithm and one key pair. A key-insulated mechanism can resolve the private key exposure problem. To ensure the security of cloud storage, we introduce the key-insulated mechanism into GSC and propose a concrete scheme without bilinear pairings in the certificateless cryptosystem setting. We provide a formal definition and a security model of certificateless key-insulated GSC. Then, we prove that our scheme is confidential under the computational Diffie-Hellman (CDH) assumption and unforgeable under the elliptic curve discrete logarithm (EC-DL) assumption. Our scheme also supports both random-access key update and secure key update. Finally, we evaluate the efficiency of our scheme and demonstrate that it is highly efficient. Thus, our scheme is more suitable for users who communicate with the cloud using mobile devices.

Attribute Based Multisignature Scheme for Wireless Communications

With rapidly development of wireless communication, more mobile devices are used in our daily life. Although the need for accessing a wireless network is evident, new problems, such as keeping and preserving user identity’s privacy, should be greatly concerned. Attribute based signature scheme is an important cryptographic primitive which provides a powerful way for user to control their privacy. In wireless environment, the capacity of wireless channel is also valuable resources which is limited. More information can be transmitted through the wireless channel when the cost of using signature to verify the message becomes less. In order to reduce the bandwidth needed to transmit attribute based signatures and keep signer’s privacy, attribute based multisignature scheme (ABMS) was proposed in this paper. Moreover, we formalize and construct the ABMS. Our scheme is existentially unforgeable against chosen message attack on Computational Diffie-Hellman (CDH) assumption in the standard model. The simulation shows that our ABMS scheme is more appropriate for wireless communication to guarantee integrity of the data.