快速解密且私钥定长的密文策略属性基加密方案

在保证密文策略属性基加密(CP-ABE)算法安全性的前提下，尽可能地提升其工作效率一直是密码学领域的研究热点。该文从作为CP-ABE效率核心的访问结构着手，首次提出基于简化有序二叉决策图(ROBDD)的访问结构，给出了相应的策略表示方法、用户可满足性判定；基于简化有序二叉决策图(ROBDD)访问结构设计了在算法时间复杂度、存储空间占用量等方面都具有较好表现的CP-ABE方案；在安全性方面，该方案能够抵抗用户间的合谋攻击和选择明文攻击。对比分析表明，ROBDD访问结构具有更强的表达能力和更高的表达效率；新的CP-ABE方案包含时间复杂度为常数阶的密钥生成算法、解密算法，能够为用户生成定长私钥并实现快速解密。

Expressive Ciphertext-policy Attribute-based Encryption Scheme with Fast Decryption and Constant-size Secret Keys

Under the premise of ensuring the security of Ciphertext-Policy Attribute Based Encryption (CP-ABE), to enhance efficiency as much as possible is always a research hotspot in the field of cryptography. Starting from the access structure, which is the efficiency basis of CP-ABE, a new kind of access structure is proposed based on Reduced Ordered Binary Decision Diagrams (ROBDD) for the first time, and the corresponding strategy representation method and satisfaction determination are given. Furthermore, based on the above access structure, a new CP-ABE with good performance in lots of aspects, such as time complexity of algorithms and storage occupancy of secret keys, is designed; In terms of security, the scheme can resist collusion attack and chosen plaintext attack. Comparative analysis shows that, ROBDD access structure has stronger expression ability and higher expression efficiency; In the new CP-ABE scheme, the time complexity of key generation algorithm and decryption algorithm is O(1), which can generate constant-size secret keys and achieve fast decryption.