格上基于身份的可问责代理重加密方案

针对目前基于格的代理重加密方案中存在密钥滥用和数字证书管理等问题,引入问责机制,提出一种新的基于身份的可问责代理重加密方案。该方案采用用户身份ID计算生成矩阵作为公钥,并使用原像采样算法提取私钥,解决了数字证书管理的问题;使用双方用户公钥计算生成重密钥,提高了加/解密时的计算效率;使用代理商公私钥参与重加密运算,完成问责算法,有效地抑制了代理商和被授权者共谋的行为。安全性分析表明方案满足选择明文攻击安全;在效率方面,方案的计算复杂度和密文开销较小。     

一种基于身份的认证加密新方案

将传统的对称加密方法与基于身份的公钥加密系统相结合,设计了一种基于身份的认证加密方案,该方案用椭圆曲线上的双线性映射构造,其安全性基于双线性的计算Diffie-Hellman假设和单向的Hash函数。与以往的文献中基于身份的公钥加密方法相比,该方案系统初始化简单、加密/解密效率高,具有较低的通信成本。     

一个高效的基于证书的加密方案

基于证书的公钥密码体制有效克服了基于身份的公钥密码体制和传统公钥密码体制中存在缺陷,成为一种颇受关注的公钥体制.以SK-IBE方案和ElGamal公钥加密方案作为构件,提出了一个高效的基于线对和基于证书的加密方案,并在随机预言模型下给出了安全性证明.在p-BDHI假设下,该方案被证明是IND-CBE-CCA安全的.在效率方面,该方案仅在解密时计算一个线对,因此方案的总体性能是高效的,经对比分析,优于现有的其它CBE方案.     

基于身份的无对密文等值测试公钥加密方案

公钥加密等值测试技术可以判断云服务器中使用了不同公钥加密的密文所对应的明文是否相同。基于传统PKI体系的密文等值测试公钥加密方案大多数是借助双线性对来实现,计算繁琐、效率偏低,同时随着用户数量增加,大量证书的生成、申请、颁发和撤销等工作愈发繁重,给系统的维护工作和可持续工作带来了挑战。针对该问题,提出了基于身份的无对密文等值测试公钥加密方案PF-IBEET,通过明文信息构造出的2点确定一条直线,利用直线实现加密、解密、授权和等值测试过程,摆脱了双线性对的限制,计算效率得到提高,同时PF-IBEET方案是在身份密码体制下构建的,解决了传统PKI体系中复杂的证书管理问题。在随机预言模型下,基于CDH和DDH数学困难问题,证明了PF-IBEET方案满足OW-ID-CCA和IND-ID-CCA安全。     

一种无信任权威的基于身份的签密方案

签密是在一个合理的逻辑步骤内同时完成数字签名和公钥加密两项功能,其计算量和通信成本都远远低于传统的先签名后加密。分析现有的基于身份的签密方案,利用双线性对提出了一种新的无需可信任中心的基于身份的签密方案,并对该方案的安全性及效率进行了分析。分析表明,该方案满足签密的安全性要求并具有更高的效率。     

基于时间分割代理加密的一般性构造方法

基于时间分割代理加密是一种典型的代理密码方案,可以将解密权委托给代理解密者,从而减轻原解密者的解密负担,具有广泛的应用前景,但研究成果相对较少。基于身份加密可直接将用户的身份标识作为公钥,简化了公钥证书的管理,近年来受到广泛关注,研究者提出很多方案。根据基于时间分割代理加密和基于身份加密在算法构成和安全模型两方面的区别与联系,提出一个基于时间分割代理加密的一般性构造方法,并证明其安全性。该方法可将任意一个安全的基于身份加密方案转换成安全的基于时间分割代理加密方案。通过该方法得到标准模型下安全的基于时间分割代理加密方案,大大丰富了基于时间分割代理加密方案的数量和类型。     

网格中基于分层的身份加密系统研究

研究了当前网格安全发展的现状,分析了身份加密(IBE)和公钥加密（PKE）算法的优缺点,从网格计算的特点和发展出发,提出了一个分层的基于身份的网格加密系统方案,并对其安全性和效率进行了分析。     

加窗的基于身份的吊销方案*

基于身份的加密(IdentityBased Encryption,IBE)作为公钥密码系统,其公钥是任意的字符串。Boneh和Franklin提出了第一个通用的基于身份的吊销方案,但该方案要求昂贵的计算和通信代价。针对上述方案,引入了加窗机制,并设计了加窗的基于身份吊销方案。对该方案的性能分析表明,它满足了密钥吊销机制的可扩展性和灵活性。     

基于无证书的两方认证密钥协商协议

两方认证密钥协商协议的设计主要基于传统公钥密码体制和基于身份的公钥密码体制.基于无证书的认证密钥协商方案避免了基于传统公钥证书方案存在的身份管理复杂性,同时也消除了基于身份方案中所固有的密钥托管问题.Park等人在2007年提出了选择身份安全模型下抗选择明文攻击(IND-sID-CPA)的无证书加密方案,在该方案的启发下提出了基于无证书体制的两方认证密钥协商方案,并与其他方案进行了安全性和有效性比较.该方案满足目前已知的绝大多数安全属性要求,特别是完美前向安全性,PKG前向安全性,已知会话相关临时秘密信息安全性以及无密钥托管等安全特性,同时保持了良好的计算效率.     

一种基于同态公钥加密的遥感影像数字指纹方案

针对非对称指纹计算复杂性高以及带宽效率低的问题,提出了一种基于同态公钥加密的遥感影像非对称指纹方案。在该方案中,内容提供商通过DCT扩频置乱方法加密遥感影像,运用Bresson同态公钥加密来实现解密密钥的非对称分发,通过客户端解密含指纹的遥感影像拷贝,使不同的解密密钥能够生成不同的含指纹拷贝。方案中公钥加密算法并未直接加密遥感影像,由此降低了计算复杂性并提高了加密效率;同时因为内容提供商只需为多个消费者生成相同的指纹拷贝,通过多播传输将其分发给不同的消费者,因此降低了带宽需求。实验表明：在用户数量较大的情况下,该方案可以有效提高带宽效率及加密效率,能够显著降低数据服务器的计算负载,减少用户等待时间。     

Secure public-key encryption scheme without random oracles

Since the first practical and secure public-key encryption scheme without random oracles proposed by Cramer and Shoup in 1998, Cramer–Shoup’s scheme and its variants remained the only practical and secure public-key encryption scheme without random oracles until 2004. In 2004, Canetti et al. proposed a generic transformation from a selective identity-based encryption scheme to a public-key encryption by adding a one-time strongly signature scheme. Since then, some transformation techniques from a selective identity-based encryption scheme to a public-key encryption have been proposed to enhance the computational efficiency, for example, Boneh–Katz’s construction and Boyen–Mei–Waters’ scheme. These transformations have either traded-off the publicly verifiable properties or tightness of security reduction. In 2007, Zhang proposed another generic transformation by adding Chameleon hash functions. In this paper, we introduce another technique from the Boneh–Boyen’s selective identity-based encryption scheme to a public-key encryption which is publicly verifiable and is slightly more efficient than Zhang’s transformation. The proposed public-key encryption scheme is based on the decisional bilinear Diffie–Hellman assumption and the target collision resistant hash functions.     

非双线性映射下一种实用的和可证明安全的IBE方案

根据MOV归约理论,采用双线性映射构造的基于身份加密方案使得该方案不具有椭圆曲线高效的优点.针对这一点,参考组合公钥体制提出了一种非双线性映射下可证明安全的基于身份加密方案,并且通过采用Katz-Wang的双公钥思想,使得该方案在随机预言机模型下的安全性证明中具有"紧"的归约.为了说明提出方案具有较好的实用性,分析了该方案的归约程度和执行效率.为了使提出方案在具有大量用户的系统中同样具有实用性,提出了多域基本模型.     

Tight chosen ciphertext attack （CCA）-secure hybrid encryption scheme with full public verifiability

In this paper, we propose a new ＂full public verifiability＂ concept for hybrid public-key encryption schemes. We also present a new hybrid public-key encryption scheme that has this feature, which is based on the decisional bilinear Diffie-Hellman assumption. We have proven that the new hybrid public-key encryption scheme is secure against adaptive chosen ciphertext attack in the standard model. The ＂full public verifiability＂ feature means that the new scheme has a shorter ciphertext and reduces the security requirements of the symmetric encryption scheme. Therefore, our new scheme does not need any message authentication code, even when the one-time symmetric encryption scheme is passive attacks secure. Compared with all existing publickey encryption schemes that are secure to the adaptive chosen ciphertext attack, our new scheme has a shorter ciphertext, efficient tight security reduction, and fewer requirements （if the symmetric encryption scheme can resist passive attacks）.     

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.     

Bit-oriented quantum public-key encryption based on quantum perfect encryption

A bit-oriented quantum public-key encryption scheme is presented. We use Boolean functions as private-key and randomly changed pairs of quantum state and classical string as public-keys. Following the concept of quantum perfect encryption, we prepare the public-key with Hadamard transformation and Pauli transformation. The quantum part of public-keys is various with different classical strings. In contrast to the typical classical public-key scheme, one private-key in our scheme corresponds to an exponential number of public-keys. We investigate attack to the private-key and prove that the public-key is a totally mixed state. So the adversary cannot acquire any information about private-key from measurement of the public-key. Then, the attack to encryption is analyzed. Since the trace distance between two different ciphertexts is zero, the adversary cannot distinguish between the two ciphertext states and also obtains nothing about plaintext and private-key. Thus, we have the conclusion that the proposed scheme is information-theoretically secure under an attack of the private-key and encryption.     

不可信更新的前向安全公钥加密方案：安全性模型和构造

已提出的不可信更新的前向安全公钥加密方案没有安全性证明,因此对方案的安全性存在质疑。对前向安全公钥加密方案进行扩展,给出首个具有可证明安全的不可信更新前向安全公钥加密方案。首先给出了不可信更新的前向安全公钥加密的方案定义和形式化安全性模型;根据方案定义,运用双线性映射技术以及高效的对称加密机制,提出一个不可信更新的前向安全公钥加密方案,并在随机预言机模型下证明了该方案的安全性。通过分析,该方案具有定长密文,定长私钥,固定加/解密开销,固定密钥更新开销的特点,具有一定的实用性。     

可证明安全的多接收者公钥加密方案设计与分析

针对现有安全广播协议密钥分发效率较低的问题,提出了一种通过多接收者公钥加密实现安全广播的方法.以Shamir的门限秘密共享方案为设计基础,首先提出了一个基于椭圆曲线上双线性变换的具有抗不可区分选择明文攻击(IND-CPA)安全性的多接收者公钥加密方案,然后对所提方案进行安全扩展,在此基础上最终提出了一个具有抗不可区分自适应选择密文攻击(IND-CCA2)安全性的多接收者公钥加密方案.基于双线性判定Diffie- Hellman假设和双线性间隙Diffie-Hellman假设,对上述所声称的IND-CPA安全性和IND-CCA2安全性进行了证明.同时,对方案的正确性及性能等进行了分析和证明.分析发现,该方案是一个安全、有效的公钥加密方案.由一个加密密钥所加密的密文可以被多个解密密钥解密而得到其所对应的明文,这使得该方案具有非常重要的应用,尤其是可以用来实现安全广播,以便在不安全的、开放的网络环境中安全地广播敏感信息.     

A protocol for establishing secure communication channels in alarge network

Knowledge exchange and information access in a truly distributed network often require transmitting of data through open media. Consequently, data presented through such an environment are vulnerable to attacks. To minimize such vulnerability, data transformation or encryption/decryption techniques are often utilized among senders and receivers to achieve secure communication. Since data encryption/decryption requires sharing of a secret session key, finding an efficient way to distribute the session key in a large-scale, truly distributed network has been a nontrivial task. This paper presents a protocol for efficiently distributing session keys in such an environment to establish a secure channel. We assume the target network consists of many locally trusted centers, and each center has many users attached to it. The scheme incorporates the public-key distribution concept and the RSA encryption scheme as the basic mathematical tools, but eliminates the storage problem associated with huge public-key files. In addition, the proposed scheme has the added feature of providing the authenticate session key to the two parties in a secure communication     

A New Public-Key Encryption Scheme

This paper proposes a new public-key encryption scheme which removes one element from the public-key tuple of the original Cramer-Shoup scheme. As a result, a ciphertext is not a quadruple but a triple at the cost of a strong assumption, the third version of knowledge of exponent assumption （KEA3）. Under assumptions of KEA3, a decision Diffie-Hellman （DDH） and a variant of target collision resistance （TCRv）, the new scheme is proved secure against indistinguishable adaptive chosen ciphertext attack （IND-CCA2）. This scheme is as efficient as Damgard ElGamal （DEG） scheme when it makes use of a well-known algorithm for product of exponentiations. The DEG scheme is recently proved IND-CCA1 secure by Bellare and Palacio in ASIACRYPT 2004 under another strong assumption. In addition to our IND-CCA2 secured scheme, we also believe that the security proof procedure itself provides a well insight for ElGamal-based encryption schemes which are secure in real world.     

New forward-secure public-key encryption without random oracles

Forward-secure public-key cryptography is an important technique for protecting private keys. It provides the benefits of frequent updating private keys without changing public keys. The most attractive property of forward security is that even if an attacker obtains the private key for the current time period, she still cannot compromise the private keys for the past time. In this paper, we newly present a forward-secure public-key encryption scheme without random oracles and prove it to be chosen-ciphertext secure in the standard model. In the proposed scheme, the ciphertext size and the decryption time have no correlation with the number of time periods and other performance indices have at most poly logarithmic complexities in terms of the number of time periods. As far as we know, it is the first forward-secure public-key encryption scheme that achieves direct chosen-ciphertext security in the standard model.