摘要：

数据隐私保护和密文可搜索性问题在云计算环境中的重要性与日俱增, 针对传统CP-ABE方案中明文形式的访问策略可能会泄露敏感信息、恶意用户撤销繁琐等问题, 提出一种具有前后向安全、可撤销和部分策略隐藏的属性基可搜索加密方案。通过公开用户属性名、隐藏用户属性值的方式实现部分策略隐藏, 避免敏感信息泄露。将用户的身份信息与二叉树叶节点关联, 用户撤销列表与密文绑定, 使得恶意用户被可信中心添加到撤销列表后将无法访问撤销前后的密文, 从而在满足前后向安全的情况下实现用户直接撤销。而云服务器仅需更新与撤销列表相关的密文, 不需要执行密钥更新, 提高了密文更新的效率。采用更新二叉树节点的随机值方式复用被撤销用户占用的二叉树节点, 实现系统中用户数量的扩容。基于q-BDHE假设, 证明所提出的方案在随机预言模型中满足选择明文攻击下的不可区分(IND-CPA)安全性。性能分析表明, 相比传统CP-ABE方案, 该方案在加密阶段的计算开销至少降低了15.3%, 在搜索验证和密文更新阶段计算开销较低。

关键词: 策略隐藏, 用户撤销, 属性基加密, 可搜索, 二叉树

Abstract:

The importance of data privacy protection and ciphertext searchability in cloud computing environments is increasing. Access policies in plain text in traditional CP-ABE schemes may leak sensitive information, and revoking malicious users is cumbersome. To address these issues, this study proposes an attribute-based searchable encryption scheme with forward and backward security, revocability, and partial policy hiding. This scheme achieves partial policy hiding by exposing user attribute names and hiding user attribute values to avoid sensitive information leakage. A user's identity information is associated with the leaves of a binary tree, and the user revocation list is bound to the ciphertext. Thus, malicious users cannot access the ciphertext before and after revocation once they are added to the revocation list by the trusted center, thereby achieving direct user revocation while meeting forward and backward security. After a malicious user is revoked, the cloud service provider only needs to update the ciphertext related to the revocation list, and no additional key update operation is required, which improves the computational efficiency of the ciphertext update. The binary tree nodes occupied by the revoked user are reused by updating the random value of the binary tree node, which increases the number of users in the system. Based on the q-Bilinear Diffie-Hellman Exponent (q-BDHE) assumption, the proposed scheme is proven to be Indistinguish ability under Chosen Plaintext Attack (IND-CPA) secure in the random oracle model. In performance analyses, computational burden reduces by at least 15.3% during the scheme's encryption stage, and the computational overhead is low in the search verification and ciphertext update phases.

Key words: policy hiding, user revocation, attribute-based encryption, searchable, binary tree