密钥弹性泄漏安全的通配模板层次委托加密机制

传统的密码方案假定密钥对可能的攻击者来说是完全隐藏的(只有算法是公开的),敌手无法获得有关密钥的任何信息.但在实际系统中,攻击者可在噪声信道或由侧信道攻击获得有关密钥的部分信息.密钥弹性泄漏安全的加密方案通过改进密码算法达到在密钥存在可能部分泄漏情况下的语义安全性.设计了一个抗密钥弹性泄漏的可委托层次模板加密方案.在该方案中,用户身份关联到含有通配符的身份模板,并可以实现再次密钥委托.该方案是抗泄漏的层次身份加密方案(hierarchical identity-based encryption,简称HIBE)和隐藏向量加密方案(hidden vector encryption,简称HVE)的一般扩展,可有效地抵抗密钥弹性泄漏,并达到自适应语义安全性.同时给出该方案的安全性证明和系统抗泄漏性能,分析显示,该方案具有较好的密钥泄漏容忍性.     

LR-FEAD: leakage-tolerating and attribute-hiding functional encryption mechanism with delegation in affine subspaces

In large-scale networks, such as cloud computing and Internet of Things, functional encryption mechanism provides a flexible and powerful cryptographic primitive in constructing the secure transmission and communication protocols. However, as the side-channel attacks in open environments, the attacker can gain partial sensitive information from the pre-defined system by virtue of the time, power analysis, cold-boot attacks, etc. In this work, we design a leakage-resilient functional encryption scheme, which tolerates amount of bounded master-key leakage and user private-key leakage. In our scheme, encryption policies are specified as point vectors and decryption roles are defined as affine subspaces. Role delegation is implemented by specifying the affine transformation over subspaces. Our scheme achieves payload hiding and attribute hiding in the sense that the attacker is able to specify any efficiently computable leakage functions and learns the function outputs taking the master/private keys as inputs. Also, our scheme can tolerate the continual leakage for master key and private key, since we can periodically update the master key and the private key to generate a new and re-randomized key with the same distribution to the previous keys. We construct the scheme in composite-order bilinear groups and prove the security with dual system encryption methodology. We also analyze and discuss the performance of allowable leakage bound, leakage ratio and possible leakage probability. Our scheme has flexible applications in secure data communication and authorization delegation in open cloud computing systems.     

Threshold public key encryption scheme resilient against continual leakage without random oracles

Threshold public key encryption allows a set of servers to decrypt a ciphertext if a given threshold of authorized servers cooperate. In the setting of threshold public key encryption, we consider the question of how to correctly decrypt a ciphertext where all servers continually leak information about their secret keys to an external attacker. Dodis et al. and Akavia et al. show two concrete schemes on how to store secrets on continually leaky servers. However, their constructions are only interactive between two servers. To achieve continual leakage security among more than two servers, we give the first threshold public key encryption scheme against adaptively chosen ciphertext attack in the continual leakage model under three static assumptions. In our model, the servers update their keys individually and asynchronously, without any communication between two servers. Moreover, the update procedure is re-randomized and the randomness can leak as well.     

Practical continuous leakage-resilient CCA secure identity-based encryption

Leakage of private information including private keys of user has become a threat to the security of computing systems. It has become a common security requirement that a cryptographic scheme should withstand various leakage attacks. In the real life, an adversary can break the security of cryptography primitive by performing continuous leakage attacks. Although, some research on the leakage-resilient cryptography had been made, there are still some remaining issued in previous attempts. The identity-based encryption (IBE) constructions were designed in the bounded-leakage model, and might not be able to meet their claimed security under the continuous-leakage attacks. In the real applications, the leakage is unbounded. That is, a practical cryptography scheme should keep its original security in the continuous leakage setting. The previous continuous leakageresilient IBE schemes either only achieve chosen-plaintext attacks security or the chosen-ciphertext attacks (CCA) security is proved in the selective identity model. Aiming to solve these problems, in this paper, we show how to construct the continuous leakage-resilient IBE scheme, and the scheme’s adaptive CCA security is proved in the standard model based on the hardness of decisional bilinear Diffie-Hellman exponent assumption. For any adversary, all elements in the ciphertext are random, and an adversary cannot obtain any leakage on the private key of user from the corresponding given ciphertext. Moreover, the leakage parameter of our proposal is independent of the plaintext space and has a constant size.     

标准模型下可证明安全的入侵容忍公钥加密方案

在传统的公钥加密方案中,一旦解密密钥泄漏,系统的安全性将完全丧失.特别是随着越来越多的加密系统被应用到移动的、安全性低的设备中,密钥泄漏显得难以避免.入侵容忍公钥加密的提出就是为了减小密钥泄漏对加密系统的危害,具有比前向安全加密、密钥隔离加密更强的安全性.在这种体制下,整个生命周期被分割成离散的时间阶段,公钥固定不变,密钥信息分享在解密者和基地中,前者独立完成解密操作,而后者则在每个时间周期中提供一个更新信息来帮助演化解密密钥.此外,每个时间段内有多次密钥刷新的操作,可以刷新解密者的密钥和基密钥.当解密者和基地被入侵时,只要不是同时被入侵,安全性就可以得到保证.即使入侵者同时入侵解密者和基地,也不会影响以前时间段密文的安全性.提出了一个入侵容忍公钥加密方案,所有费用参数关于总共时间段数的复杂性均不超过对数的平方.证明了该方案是标准模型下安全的.这是一个不需要随机预言的可证明安全的入侵容忍公钥加密方案.     

标准模型下高效的基于身份匿名广播加密方案

针对现实中广播加密的安全问题,提出一种标准模型下高效的基于身份匿名广播加密方案。匿名广播加密中广播者加密数据通过广播信道发送给用户,其中只有授权用户能够解密获得数据,同时任何人不能分辨出加密数据是发送给哪个用户的,从而保护了接收者用户的隐私。所提方案利用双系统加密技术,基于合数阶双线性群提出。同时,该方案基于静态假设,在标准模型中证明方案是选择明文安全的,密文和密钥取得了固定长度。和对比方案相比,所提方案密钥长度仅需2个群元素,同时方案满足匿名性。     

基于证书的抗泄露的安全加密方案

近期实践表明密码系统容易受到各种攻击而泄漏密钥等相关秘密信息, 泄漏的秘密信息破坏了以前的已证明安全的方案, 因此设计抗泄漏的密码学方案是当前密码研究领域的一个热点研究方向。设计一个基于证书的加密方案, 总的设计思想是使用一个基于证书的哈希证明系统, 这个证明系统包含一个密钥封装算法, 用这个密钥封装算法结合一个提取器去加密一个对称加密所用的密钥, 那么得到的加密方案就是可以抵抗熵泄漏并且是安全的。对方案的安全性分析和抗泄漏性能分析, 表明本方案在抵抗一定量的密钥泄漏和熵泄漏时可以保持安全性。     

可追踪密钥的策略隐藏属性基加密方案

传统的属性基加密方案中存在着访问策略所包含的属性会泄露用户的敏感信息以及恶意用户泄露私钥获取非法利益而不会被追责的问题。同时私钥长度、密文长度和解密运算量均会随属性数量增加而带来较大的通信开销和计算开销。针对以上问题提出了一种可追踪且隐藏访问结构的属性基加密方案。该方案在不影响加/解密效率的前提下提高了加密算法的安全性,并采用双因子身份认证机制实现了更安全高效的访问控制。并且引入一个安全的签名机制用于支持可追踪密钥来追踪恶意用户。该方案基于DBDH假设,在标准模型下被证明是安全的。     

抗密钥泄露的在线/离线身份基加密机制

目前已有的在线离线身份基加密（IBOOE）方案无法抵抗边信道攻击,引起密码系统秘密信息泄露问题。新方案通过将随机提取器嵌入在线加密算法来隐藏私钥泄露和密文之间的关系,提出首个有界泄露模型下安全的IBOOE方案;新方案基于合数阶双线性群上的三个静态假设,利用双系统加密技术在标准模型下抵抗选择明文攻击达到完全安全性和泄露弹性。此外,与传统的IBOOE方案相比较,新方案特别适用于敏感数据存储且资源受限的场景。     

用户和属性授权机构可追责的在线/离线属性基加密方案

属性基加密作为一种一对多的加密机制,能够为云存储提供良好的安全性和细粒度访问控制。但在密文策略属性基加密中,一个解密私钥可能会对应多个用户,因此用户可能会非法共享其私钥以获取不当利益,半可信的属性授权机构亦可能会给非法用户颁发解密私钥。此外,加密消息所产生的指数运算随着访问策略复杂性的增加而增长,其产生的计算开销给通过移动设备进行加密的用户造成了重大挑战。对此,文中提出了一种支持大属性域的用户和属性授权机构可追责的在线/离线密文策略属性基加密方案。该方案是基于素数阶双线性群构造的,通过将用户的身份信息嵌入该用户的私钥中实现可追责性,利用在线/离线加密技术将大部分的加密开销转移至离线阶段。最后,给出了方案在标准模型下的选择性安全和可追责证明。分析表明,该方案的加密开销主要在离线阶段,用于追责的存储开销也极低,其适用于使用资源受限的移动设备进行加密的用户群体。     

支持连接关键词搜索的属性加密方案研究

基于属性的加密机制能够实现细粒度的访问控制,支持多用户数据共享。针对大部分基于属性的可搜索加密方案存在效率低下、密钥易泄露以及仅支持单关键词搜索的问题,提出了一个支持连接关键词搜索的属性加密方案。该方案采用线性秘密共享矩阵实现访问控制,将秘密共享和恢复操作在一个与参与方属性关联的矩阵中进行,通过矩阵运算减少了计算量。在陷门生成阶段,避免直接将用户密钥提交给云服务器,保证了用户密钥的安全性。基于多项式方程实现了连接关键词搜索,缩小了搜索范围,提升了用户的搜索体验,严格的安全性分析证明方案能够达到抵抗关键字攻击安全。     

混沌系统在网络保密通信中的应用方法

混沌保密通信是当今研究信息安全的热门课题之一。该文就混沌系统应用于保密通信的基本理论,编码方式和密钥等内容作一简要讨论,并采用一次一密密码机制,用Lorenz系统的混沌输出作为密钥对文本文件进行加密和解密。这种一次一密加密方式具有很强的抗破译性。     

对一种身份型广播加密方案的分析和改进

双系统密码技术下的身份型广播加密方案具有在标准模型下, 尺寸固定的短密文和密钥, 无须随机标签和全安全等特点。研究发现该方案是不安全的, 进而提出了一种改进方案, 并在标准模型下运用双系统密码技术给出了改进方案的安全性证明。     

可公开定责的密文策略属性基加密方案

属性基加密利用属性集和访问结构之间的匹配关系实现用户解密权限的控制,从功能上高效灵活地解决了“一对多”的密数据共享问题,在云计算、物联网、大数据等细粒度访问控制和隐私保护领域有光明的应用前景。然而,在属性基加密系统中(以密文策略属性基加密为例),一个属性集合会同时被多个用户拥有,即一个解密私钥会对应多个用户,因此用户敢于共享其解密私钥以非法获利。此外,半可信的中心存在为未授权用户非法颁发私钥的可能。针对属性基加密系统中存在的两类私钥滥用问题,通过用户和中心分别对私钥进行签名的方式,提出一个密文策略属性基加密方案。该方案支持追踪性和公开定责性,任何第三方可以对泄露私钥的原始持有者的身份进行追踪,审计中心可以利用公开参数验证私钥是用户泄露的还是半可信中心非法颁发的。最后,可以证明方案的安全性基于其依赖的加密方案、签名方案。     

一种基于属性的固定密文长度广播加密方案*

针对目前基于属性的广播加密方案存在密文较长、加解密时计算花销较大等问题,提出了一种高效的密文策略的基于属性的广播加密方案。该方案基于椭圆曲线加密算法,采用动态门限访问结构,加密方可根据需要动态调整门限值。该方案仅当用户的身份信息包含在广播的授权用户集合中并且用户的属性包含在访问结构中时,解密方方可通过双线性配对运算进行密文解密。方案的密文长度及加解密双线性对运算次数固定,计算效率高并且通信开销小。仿真结果验证了方案的有效性。方案安全性是建立在q-BDHE假设之上,在标准模型下可证CPA安全。     

格上基于身份的广播加密方案

针对Wang等(WANG J, BI J. Lattice-based identity-based broadcast encryption. https://eprint.iacr.org/2010/288.pdf.)在随机预言机下提出的格基广播加密方案安全性较低且实用性较差的问题,利用盆景树扩展控制算法和一次签名算法构造了一个标准模型下基于格上错误学习(LWE)问题的身份基广播加密方案。首先利用一个编码函数替换随机预言机,将方案置于标准模型下;然后运行盆景树扩展控制算法生成用户的私钥和广播公钥;最后在加密阶段加入一次签名算法,提高方案的安全性。分析表明,相对于已有同类方案,新方案安全性较高达到了适应性攻击下选择密文安全(IND-ID-CCA)且方案具有动态扩展特性,能够通过用户身份矩阵的伸缩来实现用户的添加或删除,因此实用性较强。     

Adaptive CCA broadcast encryption with constant-size secret keys and ciphertexts

We consider designing public-key broadcast encryption schemes with constant-size secret keys and ciphertexts, achieving chosen-ciphertext security. We first argue that known CPA-to-CCA transforms currently do not yield such schemes. We then propose a scheme, modifying a previous selective CPA secure proposal by Boneh, Gentry, and Waters. Our scheme has constant-size secret keys and ciphertexts, and we prove that it is selective chosen-ciphertext secure based on standard assumptions. Our scheme has ciphertexts that are shorter than those of the previous CCA secure proposals. Then, we propose a second scheme that provides the functionality of both broadcast encryption and revocation schemes simultaneously using the same set of parameters. Finally, we show that it is possible to prove our first scheme adaptive chosen-ciphertext secure under reasonable extensions of the bilinear Diffie–Hellman exponent and the knowledge-of-exponent assumptions. We prove both of these extended assumptions in the generic group model. Hence, our scheme becomes the first to achieve constant-size secret keys and ciphertexts (both asymptotically optimal) and adaptive chosen-ciphertext security at the same time.     

高效的适应性选择密文安全公钥加密算法

安全高效的公钥加密算法是信息系统安全的重要保障技术,文中利用陷门承诺函数的思想实现对密文完整性的保护,由此在标准模型下给出一个可证明适应性选择密文攻击安全的公钥加密算法.新算法与著名的CS98公钥加密算法相比公钥参数数量减少20%,私钥参数减少80%;与BMW05公钥加密算法比较,公、私钥参数数量大为减少且安全规约效率...     

Revocable attribute-based encryption from standard lattices

Attribute-based encryption (ABE) is an attractive extension of public key encryption, which provides fine-grained and role-based access to encrypted data. In its key-policy flavor, the secret key is associated with an access policy and the ciphertext is marked with a set of attributes. In many practical applications, and in order to address scenarios where users become malicious or their secret keys are compromised, it is necessary to design an efficient revocation mechanism for ABE. However, prior works on revocable key-policy ABE schemes are based on classical number-theoretic assumptions, which are vulnerable to quantum attacks. In this work, we propose the first revocable key-policy ABE scheme that offers an efficient revocation mechanism while maintaining fine-grained access control to encrypted data. Our scheme is based on the learning with errors (LWE) problem, which is widely believed to be quantum-resistant. Our scheme supports polynomial-depth policy function and has short secret keys, where the size of the keys depends only on the depth of the supported policy function. Furthermore, we prove that our scheme satisfies selective revocation list security in the standard model under the LWE assumption.