Anonymous credit cards and their collusion analysis

Communications networks are traditionally used to bring information together. They can also be used to keep information apart in order to protect personal privacy. A cryptographic protocol specifies a process by which some information is transferred among some users and hidden from others. We show how to implement anonymous credit cards using simple cryptographic protocols. We pose, and solve, a collusion problem which determines whether it is possible for a subset of users to discover information that is designed to be hidden from them during or after execution of the anonymous credit card protocol

SHAREDWEALTH: A CRYPTOCURRENCY TO REWARD MINERS EVENLY

Bitcoin [19] is a decentralized cryptocurrency that has recently gained popularity and has emerged as a popular medium of exchange. The total market capitalization is around 1.5 billion US dollars as of October 2013 [28]. All the operations of Bitcoin are maintained in a distributed public global ledger known as a block chain which consists of all the successful transactions that have ever taken place. The security of a block chain is maintained by a chain of cryptographic puzzles solved by participants called miners, who in return are rewarded with bitcoins. To be successful, the miner has to put in his resources to solve the cryptographic puzzle (also known as a proof of work). The reward structure is an incentive for miners to contribute their computational resources and is also essential to the currency\u27s decentralized nature. One disadvantage of the reward structure is that the payment system is uneven. The reward is always given to one person. Hence people form mining pools where every member of the pool solves the same cryptographic puzzle and irrespective of the person who solved it, the reward is shared evenly among all the members of the pool. The Bitcoin protocol assumes that the miners are honest and they follow the Bitcoin protocol as prescribed. If group of selfish miners comes to lead by forming pools, the currency stops being decentralized and comes under the control of the selfish miners. Such miners can control the whole Bitcoin network [29]. Our goal is to address this problem by creating a distinct peer-to-peer protocol that reduces the incentives for the miners to join large mining pools. The central idea is to pay the “runners-up” who come close to finding a proof, thereby creating a less volatile payout situation. The work done by the “runners-up” can be used by other miners to find the solution of proof of work by building upon their work. Once they find the actual solution they have to include the solution of the other miner in order to get rewarded. The benefit of this protocol is that not only the miners save their computational resources but also the reward is distributed among the miners

An Atomicity-Generating Layer for Anonymous Currencies

Atomicity is a necessary element for reliable transactions (Financial Service Technology Consortium, 1995; Camp, Sirbu and Tygar, 1995; Tygar, 1996). Anonymity is also an issue of great importance not only to designers of commerce systems, (Chaum, 1982; Chaum, 1989; Chaum, Fiat & Naor, 1988; Medvinski, 1993), but also to those concerned with the societal effects of information technologies (Branscomb 1994. Compaine 1985, National Research Council 1996, Neumann 1993, Poole 1983). Yet there has been a tradeoff between these two elements in commerce system design. Reliable systems, which provide highly atomic transactions, offer limited anonymity (Visa, 1995; Sirbu and Tygar, 1995; Mastercard, 1995, Low, Maxemchuk and Paul, 1993) . Anonymous systems (Chaum, 1985; Chaum 1989; Medvinski, 1993) do not offer reliable transactions as shown in Yee, 1994; Camp, 1999; and Tygar, 1996. This work illustrates that any electronic token currency can be made reliable with the addition of this atomicity-generating layer.IB

Una marca de agua inteligente aplicada al dinero electrónico

International audienceEl uso de las marcas de agua se ha incrementado, principalmente por la necesidad de proteger los derechos de autor, detener copias ilegales o medir la integridad de los datos de ciertos archivos. Es bien sabido que se puede insertar código ejecutable en imágenes, pero hasta ahora solamente se ha estudiado como una amenaza de seguridad para el usuario. Nosotros proponemos utilizar esta característica de manera segura para expandir las aplicaciones actuales de las marcas de agua, dándoles exibilidad a través del código ejecutable. Presentamos el modelo de marca de agua inteligente para resolver problemas de incompatibilidad de funciones y demostramos cómo se puede aplicar este modelo a un escenario de dinero electrónico. En dicho escenario el beneciario puede manejar diferentes implementaciones de dinero electrónico mediante una aplicación estándar. Como parte de este escenario, también proponemos una máquina expendedora de dinero electrónico para ofrecer una opción de pago a los usuarios que no tienen cuenta bancaria