关键词: 云计算, 条件代理重加密, 基于证书加密, 广播加密, 随机预言模型

Abstract: To address the common issue of cloud server privilege abuse in proxy re-encryption schemes, as well as limitations of existing conditional proxy re-encryption schemes in terms of multiple recipients, security, and computational cost, a certificate-based conditional broadcast proxy re-encryption scheme was proposed. The data owner sets an access condition when generating the convertible ciphertext and re-encryption key, and the cloud server can only generate a valid re-encrypted ciphertext when the condition matches, thereby preventing the cloud server from abusing its authority and providing re-encrypted ciphertexts to unauthorized users. The security of the proposed scheme is based on the decisional Diffie-Hellman problem, and its ciphertext is proven to be indistinguishable in the random oracle model. Experimental results show that when the number of receivers is 50, compared with four contrasting schemes: Identity-Based Broadcast Proxy Re-Encryption (IB-BPRE), Privacy-Preserving Proxy Re-Encryption (PP-PRE), Revocable Identity-Based Broadcast Proxy Re-Encryption (RIB-BPRE), and Multi-Channel Broadcast Proxy Re-Encryption (MC-BPRE), the proposed scheme reduces computation time by 73.4%, 83.0%, 87.9%, and 92.3% respectively, and communication rounds by 66.5%, 90.7%, 77.5%, and 66.7% respectively, effectively enhancing efficiency and demonstrating better application prospects.

Key words: cloud computing, conditional proxy re-encryption, certificate-based encryption, broadcast encryption, random oracle model