后向无关联性的本地验证撤销群签名研究

数字签名，是密码理论的一个重要分支，在身份认证等方面举足轻重。但随着电子商务、电子政务等业务的不断展开，在多用户参与的应用环境中显得捉襟见肘。群数字签名应运而生，主要特点是保护了签名者的匿名性。 群签名撤销研究的两个主要方向：设计算量小的撤销成员算法，以及保证成员被撤销之前签名的匿名性和无关联性。目前主要有基于撤销列表（RL）和证据的撤销算法是两类主流算法，前者更适用于移动环境中。因此，在网络化、信化的今天，基于撤销列表的群签名的研究显得弥足重要。 本地验证撤销（VLR），是目前效率最高的一种基于撤销列表的方法。后向无关联性（BU），是指当成员即使在某个时段被撤销，以前的签名仍然保持匿名性。本论文主要工作，是对有群签名方案的分析和BU-VLR方案的设计，主要有以下几个方面： 1. 2007年IEEE Transactions on Vehicular Technology上的一个方案，建立在2004年Boneh等在 CRYPTO的群签名方案。本论文指出，方案使得同一成员的签名具有关联性，导致在VLR安全模型下方案不具有匿名性。 2. 分析的另外两个群签名方案，都是方案设计者在设计签名算法时由于设计不当，使得同一成员的签名具有关联性，从而导致方案在相应的安全模型下不具有匿名性。 3. 对一种基于身份的群签名方案，有文献曾对该签名方案做过分析，在本论文将给出另外一种方法来证明方案不具有匿名性。 4. 分析指出了一种新型群签名方案，其本身是建立在一个错误的签名方案之上，因而该方案不过是空中楼阁。此外，方案还存在其他缺陷。 5.构造了一个BU-VLR群签名方案，具有较短的签名长度和较低的运算量。利用k叉树扩展了方案以减少RL的数据量。最后，对2007年IEICE中一个BU-VLR方案加以改进，签名长度为原来的77.8%，运算量不变。 6.设计的第二个方案，针对现有BU-VLR方案中存在的缺陷，使得到的方案公钥长度不再与成员个数相关；撤销上的数据不再随着时间段的更新而更新，而只是在列表需要更新的时间段更新。 7.在q-SDH假设和困难性假设较强的XDH假设下，构造了一个BU-VLR群签名方案，性能上优于目前最高效的VLR方案，即BS04方案。

Application of laser cladding technology to improve the interface of thermal barrier coatings

The present study is focused on improvement of the adhesion properties of the interface between plasma-sprayed coatings and substrates by laser cladding technology (LCT), Within the laser-clad layer there is a gradient distribution in chemical composition and mechanical properties that has been confirmed by SEM observation and microhardness measurement. The residual stress due to mismatches in thermal and mechanical properties between coatings and substrates can be markedly reduced and smoothed out. To examine the changes of microstructure and crack propagation in the coating and interface during loading, the three-point bending test has been carried out in SEM with a loading device. Analysis of the distribution of shear stress near the interface under loading has been made using the FEM code ANSYS, The experimental results show clearly that the interface adhesion can be improved with LCT pretreatment, and the capability of the interface to withstand the shear stress as well as to resist microcracking has been enhanced.

Influence of the Processing Conditions on the Characteristics of the Clad Layers Produced with Laminar Plasma Technology

Laminar plasma technology was used to produce ceramic hardened layers of Al2O3-40% mass Ni composite powders on stainless steel substrates. In order to investigate the influences of processing conditions on the morphologies of the surface modified layers, two different powder-feeding methods were tested, one with carrier gas called the powder injection method, and the other without carrier gas called powder transfers method. The microscopic investigations demonstrate that the cross-section of the clad layers consists of two distinct microstructural regions, in which the Al2O3 phases exhibit different growth mechanisms. When the powder transfers method is adopted, the number density and volume fraction of the Al2O3 particles increase considerably and their distributions exhibit zonal periodical characteristics. When the powder-feeding rate increases, the microstructure of the Al2O3 phases changes from a small globular to a long needle shape. Finite element simulations show that the transient thermo-physical features of the pool substances, such as solidification rate and cooling rate, influence strongly the mechanisms of the nucleation and the directional growth of the Al2O3 phases in the thermal processing.

Applying the Electrochemical Deposition Technology to Construct the Hybrid Devices

Nanowires functionalized by special molecules can be used to as the candidates for biological application in many areas. In this paper, nickel nanowires, which were fabricated by electrochemical deposition and functionalized by biotinylated peptide, were applied to constructing the hybrid device powered by F-1-ATPase motors.