不可追踪的离线电子货币方案

针对电子货币系统中重要特性--可追踪性(traceability),本文提出一种用于不可追踪的电子货币系统的新协议.并说明基于离散对数假设(DLA)和分割选择技术的系统是安全的.     

不可追踪电子货币的实现

电子货币技术的实现是电子商务领域研究的重要课题之一,而不可追踪的电子货币的实现则是能否使电子商务普及的重要因素之一。即如何解决电子货币的匿名性和其它特性同时实现的矛盾。本文分析了理想的不可追踪的电子货币应具备的特点,运行模式及安全方案。给出了现阶段较完善的电子货币实现方案——基于RSA盲数字签名方案设计的一个在线电子货币方案和Brands系统。     

基于身份代理盲签名方案的密码学分析

盲性,也称不可追踪性,是盲签名的一个重要特性.张学军分别对蔡光兴和农强提出的基于身份的代理盲签名方案进行分析(计算机工程,2009年,第3期和第23期),指出这2个方案都不满足盲性,是可追踪的,并分别提出改进的满足盲性的方案.针对张学军对蔡光兴和农强的方案的可追踪性分析进行研究,发现张学军提出的可追踪性分析方法存在缺陷,并采用构造的方法证明代理签名人不能根据签名建立过程中记录的签名参数追踪签名,因此蔡光兴和农强提出的方案仍满足盲性,是不可追踪的.     

可追踪并撤销叛徒的属性基加密方案

属性基加密(ABE)是一种有效地对加密数据实现细粒度访问控制的密码学体制.在ABE系统中,存在恶意用户(或叛徒)泄露私钥生成盗版解码器,并将其分发给非法用户的问题.现有的解决方案仅能追查到密钥泄漏者的身份,但不能将其从ABE系统中撤销.文中提出了一种既可追踪又可撤销叛徒的属性基加密方案(ABTR).首先,给出一个具有扩展通配符的属性基加密方案(GWABE),基于3个3素数子群判定假设,采用双系统加密方法证明该GWABE方案是完全安全的.然后,利用完全子树构架将GWABE转化成ABTR方案,并证明该ABTR方案是完全安全的,且用户私钥长度是固定的.而此前的可追踪叛徒的ABE方案仅满足选择安全性.     

IT新语林

电子货币电子货币(或称为数字货币、e货币)是指利用电子手段实现的现金及其相关交易。通常涉及到使用计算机网络(如因特网)和数字储值系统。电子资金转账(EFT)就是电子货币的一个例子。它也是金融密码学及其实现技术的术语之一。一般而言,有两种类型的电子货币:具名电子货币和匿名电子货币,后者也称为数字现金。具名电子货币包含揭示原来从银行取钱人的身份信息。另外,与信用卡的方式类似,具名电子货币使得银行能够跟踪货币的流转。数字现金这是让个人通过把一个数字从一台计算机传送到另一台计算机的方式为产品或服务付款的系统。与真正…     

素数阶群上可追踪并撤销叛徒的ABE方案*

叛徒追踪和撤销是属性基加密(ABE)需要解决的问题。目前满足自适应安全且可追踪并撤销叛徒的ABE方案(ABTR)在合数阶群上构造。针对合数阶群上双线性配对计算开销过大的问题,利用对偶正交基,首先提出了一个素数阶群上具有扩展通配符的ABE方案(PGWABE),并证明该方案满足自适应安全;在此基础上,利用完全子树构架,将PGWABE方案转变为素数阶群上可追踪并撤销叛徒的ABE方案(PABTR)。与现有方案相比,该方案在同等安全性上效率更高。     

移动Ad hoc网络中身份可追踪的匿名通信方案

提出了一种适用于移动Ad hoc网的身份可追踪的匿名通信方案。方案采用伪身份的技术,基于双线性映射实现了节点间的匿名通信,同时当出现不诚实节点时,通过部分节点协作,可追踪节点的真实身份。并对该方案进行了正确性、匿名性和安全性分析。     

一个安全有效的电子支付系统

电子现金是一种非常重要的电子支付系统,具有传统货币的优点并克服其不足是设计电子现金的主要原则之一。文章设计了一个基于RSA盲签名和ElGamal签名体制的新的不可追踪的电子支付系统,并分析了它的特点和安全性。系统的主要特点是在提取协议里银行利用RSA盲签名算法签发电子现金,而在支付协议里用户用ElGamal签名体制支付现金。该电子支付系统除了具有较强的安全性,即可避免用户和银行的欺骗行为外,还具有用户一次可以提取在银行限额内的任何金额等特点。     

基于移动设备的匿名可追踪版权保护协议

提出了基于移动设备的匿名可追踪的版权管理协议。首先,它使用不断变换的临时身份来代替用户的真实 身份,使其他人不可能跟踪到用户,它关注用户动态,具有匿名性;其次,使用一次口令申请一个水印的方法来抵杭假 冒攻击;再次,采用单向哈希函数的认证方法对用户身份、数字内容进行验证;协议中的一些计算由可信中心完成,以 减少移动用户的计算量,提高效率。另外在数字产品中嵌入版权水印和指纹水印,当发现非法副本时,它可以对叛逆 者进行追踪,具有可追踪性。分析表明,该协议是安全有效的。     

基于手机的电子货币系统

介绍了当前电子货币系统的大致框架，对电子货币系统的3个主要参与方以及5个主要过程作了简要说明，然后提出了一个在手机上实现的基于防篡改硬件的电子货币系统，最后对其安全性作了分析并进行了总结。     

一种可转移的离线电子现金方案

在目前的电子现金方案中,电子现金多半不能转移。为此,提出一种用于电子支付的可转移离线电子现金方案,采用限制性盲签名进行电子现金的签发,利用可转换的部分签名进行电子现金的转移。银行和可信第三方无需在线介入每一次交易,使系统效率得到提高。安全性分析结果证明,交易过程中出现重复消费等欺诈行为时,可信第三方能撤销电子现金的匿名性,查明欺诈者。     

可转移离线电子现金

自1983年Chaum首次提出盲签名并将其用于设计不可跟踪离线电子现金以来,众多的电子现金系统相继提出,电子现金的研究已经取得了丰富的成果．电子现金的各种属性,如匿名性、不可重复花费性、可分性、公平性等,也被广泛地研究．但是,作为物理现金的一个自然属性的转移性却很少被密码学家们研究,公开文献中,涉及可转移电子现金的很少,还没有一个具体的安全的可转移电子现金方案．该文详细讨论了离线电子现金的转移性问题,描述了可转移离线电子现金的模型．第一次给出了一个具体的可转移离线电子现金方案,证明了此方案具备不可伪造性、不可跟踪性、不可重复花费性、不可陷害性等安全属性,并对可转移电子现金的效率问题进行了分析．     

Ownership-attached unblinding of blind signatures for untraceable electronic cash

In an untraceable electronic cash protocol based on blind signatures, an identified customer can withdraw a blinded electronic cash from the bank and the unblinding operation is adopted by the customer to transform the blinded electronic cash into a valid one. Before performing the operation, the blinded electronic cash is protected well since attackers cannot convert it into a valid electronic cash without the blinding factor corresponding to the operation. However, after unblinding, the electronic cash will suffer from the theft attacks since it is not protected by any security mechanism. This paper introduces a new unblinding operation called ownership-attached unblinding which attaches the identities of a designated payee and a specified transaction to the blinded electronic cash and then produces an ownership-attached electronic cash other than a bare one such that the cash can withstand the theft attacks during the entire transaction because it is valid for the designated payee and the specified transaction only. Furthermore, the proposed scheme does not largely increase the computation cost required for each customer so that it also is a customer efficient protection solution for untraceable electronic cash and especially suitable for mobile clients and smart-card users.     

基于动态加权组合模型的ATM现金预测方法

本文提出了一种基于动态加权组合模型的智能现金预测方法, 可以对银行ATM设备的日常现金用量进行精准预测, 为日常现金调拨管理提供决策依据. 与以往使用的单算法预测不同, 本文对银行业务、交易流水与设备等特性进行分析, 据此组合4种单一机器学习模型, 提出并实现基于动态加权组合模型的智能算法. 该算法可以为银行现金用量管理提供更智能、更精准、更高效的预测手段, 有效压降现金库存总量与回钞率, 提升现金运用率. 此方法已在广东、重庆、江西、山西、北京等地区使用, 并取得良好效果.     

加入概率检验的Brands数字现金改进方案算法

Brands方案已经成为一个经典的数字现金方案,在这个方案的基础上设计了各种各样的数字现金方案,文章提出的方案是在原有的Brands方案的基础上增加一个概率检验过程,通过对用户信用和通信线路的综合考虑决定是否对数字现金作实时的检查,使数字现金使用的安全性得到极大的提高。     

ATM现金流量动态分析

根据ATM现金流量时间序列,分析ATM的取款量变化规律．用Matlab作为建模和分析工具,通过模型识别和参数估计建立自回归滑动平均模型,刻画ATM上现金流的变化规律,检验模型的正确性．在此基础上可预测未来10天的ATM现金流量,对银行现金的准备和调配工作具有重要意义．     

On supply chain cash flow risks

This study models the supply chain related cash flow risks for a business entity measured by the standard deviations of cash inflows, outflows, and netflows of each period in a planning horizon. The goal is to provide an insightful look on how common practices that intend to improve the Cash Conversion Cycle (CCC), e.g., offering early payment discounts, may contribute to cash flow risks. We show the benefits and recommend the best policy of using Asset-Backed Securities (ABS) to finance accounts receivable as a means to shorten the CCC and lower the cash inflow risk. It is particularly helpful to small vendors having tight cash reserves and high financing costs.     

基于绝对最小树形图的跨行资金归集模型

跨行资金归集就是将集团内下级单位在非单一银行开设的账户内的资金上收至集团账户的过程。其目的在于提高集团企业整体的资金使用率。但是由于归集业务发生频繁,企业对银行间的手续费用支出骤增,企业获利也随之骤减。提出了基于绝对最小树形图的跨行资金归集模型,并验证了企业采用此模型后,手续费用会降至最低,使企业在提高资金使用率时,有效控制了费用支出。     

A joint model for cash and inventory management for a retailer under delay in payments

As retail companies continue to navigate through the economy downturn, it becomes critical to find innovative cost reduction methods. Cash management is a cost-intensive process for retailers, who are currently focusing on effective cash management, such as deciding on the maximum cash level to keep in their business accounts and how much to borrow to finance inventories and pay suppliers. In this paper, we consider the problem of finding the optimal operational (how much to order and when to pay the supplier) and financial decisions (maximum cash level and loan amount) by integrating the cash management and inventory lot sizing problems. We consider a supplier offering a retailer an interest-free credit period for settling the payment. Beyond this period, the supplier charges interest on the outstanding balance. Whenever the cash exceeds a certain limit, it will be invested in purchasing financial securities. At the time when the retailer pays the supplier for the received order, cash is withdrawn from the account, incuring various financial costs. If the cash level becomes zero or not sufficient, the retailer obtains an asset-based loan at interest. We model this problem as a nonlinear program and propose a solution procedure for finding the optimal solution. We perform a numerical study to analyze the impact of optimal cash management on the inventory decisions. The results indicate that the optimal order quantity decreases as the retailer’s return on cash increases. We compare our model to a model that ignores financial considerations of cash management, and show numerically that our model lowers the retailer’s cost. Also, we illustrate the effect of changing various model parameters on the optimal solution and obtain managerial insights.     

Decision support for integrated cash management

Cash management has attracted the increasing attention of both academicians and practitioners in recent time. The expanding role and responsibilities of cash managers and corporate treasurers is likely to increase the focus on cash management as a vital organizational function. Academic research, however, has primarily focused on providing analytical tools to solve well structured problems that are relatively isolated in nature. Conspicuously, no attempt has been made to integrate the various sub-problems of cash management explicitly recognizing interrelationships among the sub-problems as well as between the sub-problems and other financial decisions. More importantly, there is an even greater need to provide a framework that in addition to recognizing the above interrelationships will enable the cash manager to recognize a more inclusive set of dependencies that exist in practice.Decision support systems have the potential to overcome the above deficiencies to a significant extent. This paper is aimed at providing a conceptual framework for designing an effective model-based decision support system (DSS) for integrated cash management. The framework should form a useful basis for any attempts at designing computer-based support systems for cash management.