Positive Solutions Bifurcating from Zero Solution in a Lotka-Volterra Competitive System with Cross-Diffusion Effects

A strongly coupled elliptic system under the homogeneous Dirichlet boundary condition denoting the steady-state system of the Lotka-Volterra two-species competitive system with cross-diffusion effects is considered. By using the implicit function theorem and the Lyapunov- Schmidt reduction method, the existence of the positive solutions bifurcating from the trivial solution is obtained. Furthermore, the stability of the bifurcating positive solutions is also investigated by analyzing the associated characteristic equation.

Pattern formation induced by cross-diffusion in a predator-prey system

This paper considers the Holling-Tanner model for predator-prey with self and cross-diffusion. From the Turing theory, it is believed that there is no Turing pattern formation for the equal self-diffusion coefficients. However, combined with cross-diffusion, it shows that the system will exhibit spotted pattern by both mathematical analysis and numerical simulations. Furthermore, asynchrony of the predator and the prey in the space. The obtained results show that cross-diffusion plays an important role on the pattern formation of the predator-prey system.

Global Existence of Solutions to the Prey-predator System of Three Species with Cross-diffusion

The prey-predator system of three species with cross-diffusion pressure is known to possess a local solution with the maximal existence time T ≤ ∞.By obtaining the bounds of W21-norms of the local solution independent of T,it is established the global existence of the solution.

Spatial Pattern Induced by Cross-Diffusion in a Chemostat Model with Maintenance Energy

A chemostat model with maintenance energy and crossdiffusion is considered,and the formation of patterns is caused by the cross-diffusion. First, through linear stability analysis, the necessary conditions for the formation of the spatial patterns are given. Then numerical simulations by changing the values of crossdiffusions in the unstable domain are performed. The results showthat the cross-diffusion coefficient plays an important role in the formation of the pattern, and the different values of the crossdiffusion coefficients may lead to different types of pattern formation.

Turing pattern selection for a plant-wrack model with cross-diffusion

We investigate the Turing instability and pattern formation mechanism of a plant-wrack model with both self-diffusion and cross-diffusion terms.We first study the effect of self-diffusion on the stability of equilibrium.We then derive the conditions for the occurrence of the Turing patterns induced by cross-diffusion based on self-diffusion stability.Next,we analyze the pattern selection by using the amplitude equation and obtain the exact parameter ranges of different types of patterns,including stripe patterns,hexagonal patterns and mixed states.Finally,numerical simulations confirm the theoretical results.

Turing Instability and Pattern Induced by Cross-Diffusion for a Nonlinear Reaction-Diffusion System of Turbulence-Shear Flow Interaction

The Turing instability and the phenomena of pattern formation for a nonlinear reaction-diffusion(RD) system of turbulence-shear flowinteraction are investigated.By the linear stability analysis,the essential conditions for Turing instability are obtained.It indicates that the emergence of cross-diffusion terms leads to the destabilizing mechanism.Then the amplitude equations and the asymptotic solutions of the model closed to the onset of instability are derived by using the weakly nonlinear analysis.

Global existence of weak solutions to a prey-predator model with strong cross-diffusion

Using finite differences and entropy inequalities, the global existence of weak solutions to a multidimensional parabolic strongly coupled prey-predator model is obtained. The nonnegativity of the solutions is also shown.

Attribute-Based Access Control for Multi-Authority Systems with Constant Size Ciphertext in Cloud Computing

In most existing CP-ABE schemes, there is only one authority in the system and all the public keys and private keys are issued by this authority, which incurs ciphertext size and computation costs in the encryption and decryption operations that depend at least linearly on the number of attributes involved in the access policy. We propose an efficient multi-authority CP-ABE scheme in which the authorities need not interact to generate public information during the system initialization phase. Our scheme has constant ciphertext length and a constant number of pairing computations. Our scheme can be proven CPA-secure in random oracle model under the decision q-BDHE assumption. When user's attributes revocation occurs, the scheme transfers most re-encryption work to the cloud service provider, reducing the data owner's computational cost on the premise of security. Finally the analysis and simulation result show that the schemes proposed in this thesis ensure the privacy and secure access of sensitive data stored in the cloud server, and be able to cope with the dynamic changes of users' access privileges in large-scale systems. Besides, the multi-authority ABE eliminates the key escrow problem, achieves the length of ciphertext optimization and enhances the effi ciency of the encryption and decryption operations.

The Cloud Storage Ciphertext Retrieval Scheme Based on ORAM

Due to its characteristics distribution and virtualization, cloud storage also brings new security problems. User＇s data is stored in the cloud, which separated the ownership from management. How to ensure the security of cloud data, how to increase data availability and how to improve user privacy perception are the key issues of cloud storage research, especially when the cloud service provider is not completely trusted. In this paper, a cloud storage ciphertext retrieval scheme based on AES and homomorphic encryption is presented. This ciphertext retrieval scheme will not only conceal the user retrieval information, but also prevent the cloud from obtaining user access pattern such as read-write mode, and access frequency, thereby ensuring the safety of the ciphertext retrieval and user privacy. The results of simulation analysis show that the performance of this ciphertext retrieval scheme requires less overhead than other schemes on the same security level.

Broadcast group-oriented encryption secure against chosen ciphertext attack

A novel broadcast encryption scheme for group communication scenarios in distributed networks is presented. In the scheme, anyone is allowed to encrypt a message and distribute it to a designated group. Each member in the designated group has the ability to independently decrypt a ciphertext. In contrast to traditional broadcast encryption, all the valid receivers in the proposed scheme compose the designated group. To take advantage of this property, a tab for the group is set and the matching private key for each member is generated. In addition, before decrypting a ciphertext, anyone in the scheme can verify the ciphertext, to ensure that the ciphertext is correct. This property is very important for large-scale group communication, as the gateway can filter incorrect ciphertext and alleviate the receiver＇s workload. Finally, a proof in the random oracle model is given, to show that the proposed scheme is secure against the adaptively chosen ciphertext attack.

A Practical Approach to Attaining Chosen Ciphertext Security

Strong security in public key cryptography is not enongh; the encryption has to be achieved in an efficient way. OAEP or SAEP is only suitable for special applications （e. g. key transport）, and securely transporting message of any length is a challenge. Motivated by the hybrid encryption, we present a practical approach to achieve the （adaptively） chosen eiphertext security. The time cost of encryption/decryption of proposed scheme is similar to OAEP and the bandwidth of message recovery is 92% for standard security parameter, while RSA-OAEP is 84%. The scheme is also provably secure against adaptively chosen ciphertext attacks in the random oracle model. We conclude that the approach is practical in more extensive application.

Chosen-Ciphertext Attack Secure Public-Key Encryption with Keyword Search

As the use of cloud storage for various services increases,the amount of private personal information along with data stored in the cloud storage is also increasing.To remotely use the data stored on the cloud storage,the data to be stored needs to be encrypted for this reason.Since“searchable encryption”is enable to search on the encrypted data without any decryption,it is one of convenient solutions for secure data management.A public key encryption with keyword search(for short,PEKS)is one of searchable encryptions.Abdalla et al.firstly defined IND-CCA security for PEKS to enhance it’s security and proposed consistent IND-CCA secure PEKS based on the“robust”ANO-CCA secure identity-based encryption(IBE).In this paper,we propose two generic constructions of consistent IND-CCA secure PEKS combining(1)a hierarchical identity based encryption(for short,HIBE)and a signature scheme or(2)a HIBE,an encapsulation,and a message authentication code(for short,MAC)scheme.Our generic constructions identify that HIBE requires the security of a signature or a MAC as well as the weaker“ANO-CPA security(resp.,IND-CPA security)”of HIBE than“ANOCCA security(resp.,IND-CCA security)”of IBE required in for achieving IND-CCA secure(resp.,consistent)PEKS.Finally,we prove that our generic constructions satisfy IND-CCA security and consistency under the security models.

Secured Access Policy in Ciphertext-Policy Attribute-Based Encryption for Cloud Environment

The cloud allows clients to store and share data.Depending on the user’s needs,it is imperative to design an effective access control plan to share the information only with approved users.The user loses control of their data when the data is outsourced to the cloud.Therefore,access control mechanisms will become a significant challenging problem.The Ciphertext-Policy Attribute-Based Encryption(CP-ABE)is an essential solution in which the user can control data access.CP-ABE encrypts the data under a limited access policy after the user sets some access policies.The user can decrypt the data if they satisfy the limited access policy.Although CP-ABE is an effective access control program,the privacy of the policy might be compromised by the attackers.Namely,the attackers can gather important information from plain text policy.To address this issue,the SHA-512 algorithm is presented to create a hash code for the user’s attributes in this paper.Depending on the created hash codes,an access policy will be formed.It leads to protecting the access policy against attacks.The effectiveness of the proposed scheme is assessed based on decryption time,private key generation time,ciphertext generation time,and data verification time.

Novel dynamic anti-collusion ciphertext policy attribute-based encryption scheme in 5G D2D environment

To share data securely with secure attribute revocation,anti-collusion,and dynamic user management in the 5G device-to-device(D2D)environment,a novel dynamic anti-collusion ciphertext policy attribute-based encryption(NDA-CP-ABE)scheme in the 5G D2D environment is proposed.On the basis of the ciphertext policy attribute-based encryption algorithm,fine-grained access control and secure attribute revocation are realized,and the confidentiality of data is guaranteed.A polynomial function is adopted in the ciphertext generation phase to realize dynamic user management.A random number is used to prevent a collusion attack among the legitimate user equipment(UE),revoked UE,and external network attackers.Finally,on the basis of the Diffie-Hellman problem,the NDA-CP-ABE scheme is formally proved,and the simulation performances are compared with those of similar schemes.The results show that data can be securely shared through a D2D channel with secure attribute revocation,anti-collusion,and dynamic user management.Moreover,compared with similar schemes,the NDA-CP-ABE scheme has higher efficiency in encryption,decryption,and storage.

智慧医疗系统中可容错的多维度密文跨域聚合方案

为解决智慧医疗系统中数据孤岛问题,实现医疗数据安全汇聚的目标,同时确保医疗数据传输与存储过程的机密性、完整性与可用性,提出了支持传输容错的可验证多维医疗密文跨域聚合方案。该方案将边缘服务器集成到传统的云计算架构,通过设计同态加密算法,并结合Shamir秘密共享技术,实现多维度加密数据可传输容错的2层聚合。该方案设计了基于椭圆曲线的数字签名算法,确保医疗加密数据在传输与存储过程中的完整性。医疗数据分析中心可以向云服务器灵活选取目标区域进行跨域聚合,并借助云审计机制对获取到的聚合结果进行轻量级完整性验证。根据霍纳法则,医疗数据分析中心利用解密私钥可以直接获得相应区域终端用户各个维度医疗数据的聚合结果。通过安全性分析与性能比较表明,该方案能够安全高效地部署在智慧医疗系统。

面向物联网的基于智能合约与CP-ABE的访问控制方案

随着物联网设备数量激增,传统的集中式访问控制方案在面对当前大规模物联网环境时显得力不从心,现有的分布式访问控制方案存在高货币成本和处理访问请求的低吞吐量等问题。针对这些问题提出一种区块链智能合约结合密文策略属性基加密(ciphertext policy attribute based encryption,CP-ABE)实现对物联网资源的访问控制方案。以超级账本(Hyperledger Fabric)为底层网络,对功能令牌执行属性基加密,利用星际文件系统(interplanetary file system,IPFS)保存令牌密文,通过智能合约公开令牌获取地址实现一对多授权。进一步设计合约部署到区块链实现对令牌请求的去中心化权限评估,维护主体在特定资源对象上允许的操作,实现更为细粒度的属性访问控制。仿真实验及性能分析表明,所提方案与现有方案相比能够使数据所有者在更短的时间内完成对大量请求主体的安全访问授权,压力测试表明链码具有较好性能。

复杂网络环境下动态可信大数据加密共享仿真

在复杂网络环境下,由于涉及多个参与方和节点,且受网络环境的复杂程度、海量数据以及数据可能存在泄露、丢失等风险影响,使得数据共享的可靠性和完整性降低。为了解决上述问题,提出一种复杂网络环境下动态可信大数据加密共享方法。利用区块链技术设计网络可信大数据共享结构,采用乘法循环群、哈希函数确定数据共享安全相关参数,并生成公钥、私钥,通过Verify Public Key函数检测公钥、私钥合格性,利用CSCLPRE算法对可信数据加密,并将加密后结果传输到指定位置,当接收到密文后校验其正确性,采用秘钥对其解密,完成可信大数据的共享。实验结果表明,所提方法能够有效防御各种攻击行为,加密、解密耗时低于6ms,且隐私、机密数据被盗取、篡改概率低,能够保证可信大数据完整共享。

基于混沌序列的电子档案上传加密方法

为了提升数据的存储效率和电子档案的传输安全性,设计了一种基于混沌序列的电子档案上传加密方法(混沌序列方法).以形式化方案分解电子档案上传步骤,在交互过程中统一定义上传形式.采用Logistic映射关系表示混沌模式;给定混沌序列变化区间,随机生成档案加密密钥流;在保证电子档案可完整解密的前提下,设定密文置换规则,设置置换流程,根据可逆关系调整密文顺序,完成电子档案的加密上传.在光纤网络配置基础上模拟电子档案上传全过程,实验结果表明,混沌序列方法能够在10 s内生成128 bit加密密钥,且在规定时间内完成498组1.5 GB内存大小的电子档案传输.

云存储抗边信道攻击的密文数据去重算法

考虑云储存中密文数据相似性较高,导致去重难度过大的问题,提出一种基于执行机构的密文数据去重算法。构建密文动态平衡跳跃表,根据对动态平衡跳跃表的构建与描述,得到抗边信道攻击的密文数据动态叠加特点。基于密文动态平衡跳跃表构建与更新结果,提出一种抗边信道攻击的数据去重框架,云储存提供商执行数据加密、数据标签查询以及数据去重三个过程。云端储存使用标签代表数据查询操作,一旦查询计数超过阈值,执行数据加密程序对该文件进行加密,并按照云储存服务商提供的执行命令对重叠密文进行去重。实验结果证明,所提方法对密文数据去重效果表现较佳,去重后云储存空间占用情况得到了明显改善。

基于密文域敏感信息表征的隐私保护算法

网络中提供身份信息的网络资源容易导致个人身份数据的泄露,为了保障身份信息安全,需要进行信息隐私保护设计,提出一种基于密文域敏感信息表征的隐私保护算法.采用双线性映射编码技术构建表征个人隐私信息的比特序列信息模型,提取比特序列信息的信息熵特征量,在密文域中对提取的特征量进行混沌加密设计.设计隐私保护敏感信息的密钥构造方案,运用到数字签名中,对每组信息进行分块加密和身份认证,实现隐私保护设计.仿真结果表明,采用该算法进行隐私保护,对用户敏感信息加密后的抗攻击性能较好,模型的可信度较高,具有较好的隐私保护能力.