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一种无密钥托管的基于身份的在线/离线加密方案
何能强,李叶,张华
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(国家计算机网络应急技术处理协调中心, 北京 中国 100029;北京邮电大学网络与交换技术国家重点实验室, 北京 中国 100876)
摘要:
随着基于身份的加密算法发展研究,在线/离线技术被认为是一个可以有效提升密钥生成和加密时计算效率的方法。在离线时,很大比例的运算可在明确加密消息和接收方的身份之前完成。当在线时,方案只需要少量的计算便可完成密钥生成和加密。本文提出了一种高效的基于身份的在线/离线加密方案,首次使用可选择公用外包密钥生成中心(Outsourced key generator,OKG),解决了之前PKG可单独解密出任意密文的密钥托管问题。在本文的方案中,除非私钥生成中心(Private key generator,PKG)与OKG合谋,否则PKG和OKG都不能单独解密出密文消息。在基于身份的在线/离线加密系统建立之后,用户也可根据对所属PKG的信任程度选择是否使用公用OKG,而不需要PKG重新初始化。方案为减少用户的解密计算代价,可扩展支持云外包解密,解密算法中的大部分运算可以外包给云完成。除此之外,对比于其他现行方案,本方案在密钥生成算法中也可采取在线/离线技术。论文在随机预言机模型下,证明了本文的方案在弱l-BDHI假设下是IND-ID-CPA安全的。最后的效率分析表明本文的方案在计算复杂度和存储开销方面都具有优势。
关键词:  基于身份的加密  在线/离线密钥生成和加密  外包密钥生成中心  解密可外包  密钥托管问题  可证明安全
DOI:10.19363/j.cnki.cn10-1380/tn.2018.03.03
投稿时间:2017-10-13修订日期:2018-02-02
基金项目:本课题得到国家自然科学基金项目(No.61502044)资助。
An Identity-Based Online/Offline Encryption Scheme without Key Escrow
HE Nengqiang,LI Ye,ZHANG Hua
National Computer Network Emergency Response Technical Team/Coordination Center of China(CNCERT/CC), Beijing 100029, China;State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100876, China
Abstract:
With the development of Identity-Based Cryptograph, the online/offline technology is considered to be a promising way to accelerate the computation of key extraction and encryption, because a large proportion of computation will be pre-computed in the offline phase before knowing the message to be encrypted and recipient's identity. Light computation is required in the online phase for key generation and message encryption. In this paper, we propose a novel efficient identity-based online/offline encryption with public optional Outsourced Key Generator (OKG) scheme. The OKG is applied in our scheme to remove the inherent key escrow problem. Unless the Private Key Generator (PKG) colludes with OKG, neither PKG nor OKG can decrypt the ciphertext independently. Users can according to their confidence of PKG to choose whether to use the public OKG after set up the IBOOE system. To reduce the user's decryption computational cost, this scheme can support outsourced decryption. The most part of decryption computation can be done by outsourcing cloud. Besides, the key generation algorithm can also adopt the technique of online/offline. Furthermore, we present the proposed scheme can get IND-ID-CPA security based on the weak l-BDHI assumption in the random oracle model. The efficiency analysis shows that the scheme has advantages in terms of computation complexity and storage overhead.
Key words:  identity-based encryption  online/offline key generation and encryption  outsourced key generator  outsourced decryption  key escrow  provable security