Cryptanalysis of an identity-based public auditing protocol for cloud storage

Public verification of data integrity is crucial for promoting the serviceability of cloud storage systems. Recently, Tan and Jia （2014） proposed an identity-based public verification （NaEPASC） protocol for cloud data to simplify key management and alleviate the burden of check tasks. They claimed that NaEPASC enables a third- party auditor （TPA） to verify the integrity of outsourced data with high efficiency and security in a cloud computing environment. However, in this paper, we pinpoint that NaEPASC is vulnerable to the signature forgery attack in the setup phase; i.e., a malicious cloud server can forge a valid signature for an arbitrary data block by using two correct signatures. Moreover, we demonstrate that NaEPASC is subject to data privacy threats in the challenge phase; i.e., an external attacker acting as a TPA can reveal the content of outsourced data. The analysis shows that NaEPASC is not secure in the data verification process. Therefore, our work is helpful for cryptographers and engineers to design and implement more secure and efficient identitv-based nublic alldit^n~ .~cheme~ far clnne] ~tnr^q~

数据完整性公开验证对提高云存储系统的适用性、可服务性至关重要。最近,Tan和Jia(2014)提出了一种基于身份的云数据完整性公开验证(NaEPASC)协议,以简化用户密钥管理和减轻完整性验证负担。NaEPASC可以使第三方审计人员(third-party auditor,TPA)能够在云计算环境中高效和安全地验证外包数据的完整性。然而,本文指出NaEPASC在数据签名阶段容易遭受签名伪造攻击,即恶意云服务器可以通过使用两个正确的签名来伪造任意数据块的有效签名。此外,证明了NaEPASC在挑战阶段受到数据隐私威胁,即TPA或冒充TPA的外部攻击者可以分析出外包数据的内容。本文分析表明NaEPASC在数据验证过程中不安全。本文的工作有助于密码学家和工程师设计、实施更安全高效的基于身份的云存储数据完整性公开审计方案。