As a distributed extension of ciphertext-policy attribute-based encryption (CP-ABE), multi-authority ABE (MA-ABE) does not require the participation of a trusted central authority and has a wider application prospect in the decentralized background of the cloud computing environment. We propose the first MA-ABE scheme supporting multi-fan-in circuits and collusion-resistance on prime-order bilinear groups and prove the fully adaptive security based on the matrix decision Diffie-Hellman (MDDH) assumption. Compared with the only two fully adaptively secure MA-ABE schemes, our scheme enjoys shorter parameters, which has lower ciphertext and key size, and supports many-use of attribute.

Attribute-based encryption (ABE) is crucial for ciphertext access control in cloud settings. In this paper, we evaluate the resilience of classical ABE schemes to specific attacks, ensuring only robust schemes are employed and informing the design of secure ABE schemes. We demonstrate an attribute-key attack on two ciphertext-policy ABE (CP-ABE) schemes using illegitimate private keys. To quantify the security of private keys against collusion, we propose a novel attribute-key security model. At last, we present a hidden-policy CP-ABE (HP-CP-ABE) scheme, proving its selective security and resistance to collusion attacks.

The identity-based encryption (IBE) scheme takes the user's identity as the public key, which avoids the disadvantages of digital certificate management. Lattice-based IBE scheme has the advantages of resistant to quantum attack, high efficiency and simple structure, and has become a research hotspot in the field of post-quantum information security. In this paper, an IBE scheme is designed based on NTRU lattice, and the hybrid sampling algorithm proposed by Ducas and Prest is used in the private key extraction algorithm of the scheme, which improves the implementation efficiency of the key generation algorithm while ensuring the security of the private key. The encryption and decryption algorithm of the IBE scheme is designed by using the framework structure of the encryption algorithm based on the LWE problem. Under the condition that the NTRU difficulty hypothesis and the LWE difficulty hypothesis hold simultaneously, the scheme is proved to have indistinguishability under chosen plaintext attack with identity-based encryption (IND-ID-CPA). The software implementation of the scheme and the efficiency under the specific parameter settings are given, and the experimental results show that the new scheme has higher encryption and decryption efficiency and shorter ciphertext length than the typical lattice IBE scheme.

Abstract The attribute-based encryption (ABE) scheme is suitable for access control of ciphertext in cloud computing. Kowalczyk and Wee proposed an adaptively secure attribute encryption scheme that supports $NC^1$ circuits. However, the circuit depth increases because this scheme supports only circuits with fan-in 2, which increases the key length and computational complexity of the key generation and decryption algorithms. To improve efficiency, we designed a secret sharing scheme for circuits with fan-in $n$, and we proposed a key-policy ABE scheme that supports circuits with fan-in $n$. We also designed pebbling rules for secret sharing in circuits with fan-in $n$, improving the compactness of the security reduction. Finally, we proved the adaptive security of the scheme by using a piecewise guessing framework and dual-system encryption. Compared with existing schemes, our scheme reduces the key size, improves the efficiency of the key generation algorithm and the decryption algorithm and provides tighter security reduction.

Multiplication on polynomial rings has been widely used in public-key cryptographic schemes based on ideal lattices. It is an important module that significantly affects the efficiency of the schemes. Improved Preprocess-then-NTT (IPtNTT) is an algorithm which can fast realize multiplication on polynomial rings. Compared with the Number Theoretic Transform (NTT), the IPtNTT weakens the parameter restriction of lattice-based public-key cryptographic schemes. By optimizing the IPtNTT with the AVX2 instruction set, we reduce the clock cycles consumed by multiplication on polynomial rings to 15%–22%. According to the experimental results, we give specific suggestions on using AVX2 optimized IPtNTT to realize multiplication on polynomial rings with different parameters chosen in lattice-based public-key cryptosystems.

Attribute-based encryption achieves fine-grained access control, especially in a cloud computing environment. In a ciphertext-policy attribute-based encryption (CP-ABE) scheme, the ciphertexts are associated with the access policies, while the secret keys are determined by the attributes. In recent years, people have tried to find more effective access structures to improve the efficiency of encryption systems. This paper presents a ciphertext-policy attribute-based encryption scheme that supports arithmetic span programs. On the composite-order bilinear group, the security of the scheme is proven by experimental sequence based on the combination of composite-order bilinear entropy expansion lemma and subgroup decision (SD) assumption. And, it is an adaptively secure scheme with constant-size public parameters.