11-04-2014, 01:21 PM
Design of Ecash system with fairness property
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INTRODUCTION
Electronic cash systems have been widely discussed in past years in regards to many significant issues, such asanonymity, untraceability, unforgeability, unreuseability, non-repudiation and so on. Nevertheless, there still existsome problems between customers and merchants when an e-cash system is implemented on the Internet. For example, a customer who has paid electronic cash to a merchant cannot ensure that the merchant will send the goods which he has paid for. Similarly, a merchant who has sent goods to a customer also cannot ensure that the customer will send payment. To solve these problems, we integrate fair exchange with the payment protocol of our e-cash system.
Behind the scenes banks, credit-card companies, and other financial institutions have been processing transactions electronically for several decades now. Two important developments that will open up the field of electronic payment systems are now taking place. First, the prospect of electronic commerce over the Internet is creating a large demand for electronic payment methods for open networks. Second, the introduction of nation-wide electronic purse schemes is creating many more places and situations where smart cards can be used for cost-effective off-line payments.
Ecash:
E-cash technology is used by a number of banks around the globe. These banks issue e-cash to their customers, who can then spend it at affiliated merchants on the Internet.
There are two different types of electronic cash systems: on-line e-cash and off-line e-cash. In an on-line e-cash system, the issuing bank should participate in the payment protocol to verify the coin. The online e-cash architecture can be combined with an arbitrary blind signature scheme to create an anonymous e-cash scheme. This may be a straightforward way to make sure of the validity of payments, but it is inefficient for real-time transactions. An off-line system can enhance performance in which the bank is not required to be present to verify the coin during the payment procedure.
Cryptography Basis
Cryptography is the science of using mathematics to encrypt and decrypt data. A text that can be read without any special measures is called plaintext. Encrypting this text consist in applying a mathematical function that disguise it in such a way as to hide its substance. The result is called cipher text. The opposite way, transforming a cipher text into a plaintext, is called decryption.
Cryptography allows two people to exchange data through an insecure channel, like Internet. The sender encrypts the plaintext and sends the resulting cipher text. The receiver decrypts this cipher text and gets the initial plaintext. Even if a third person is listening and intercepting every message, he only gets cipher texts, which is completely useless if he doesn't know the secret key used. But cryptography is not only limited to hiding data.
Asymmetric cryptography
Symmetric cryptography is fast and secure. But how is it possible to exchange the secret key in a secure manner? We can for example exchange it through another channel, like the phone. Or store the private key in a floppy and give it physically to the receiver. Of course they are a lot of solutions, but they are not very handy. And what if you need to communicate securely with someone you've never met, or how to establish a secure channel between you and your bank to make e-banking?
The solution is called asymmetric cryptography, and is certainly one of the most innovations in the field. The concept was introduced by Whitfield Diffie and Martin Hellman in 1975. The idea is to use two keys, one for encryption and the other for decryption.
ELECTRONIC CASH-A REVIEW
E-cash truly globalizes the economy, since the user can download money into his softcash-wallet in any currency desired. A merchant can accept any currency and convert it to local currency when the softcash is uploaded to the bank account.
In essence, E-cash combines the benefits of other transaction mediums. Thus, it is similar to debit/credit cards, but E-cash allows individuals to conduct transactions with each other. It is similar to personal checks, but it is feasible for very small transactions. While it appears superior to other forms, E-cash will not completely replace paper currency. Use of E-cash will require special hardware, and while most people will have access, not all will. However, E-cash presents special challenges for the existing "middlemen" of the current paper currency society. More and more, banks and other financial intermediaries will serve simply as storehouses for money, lenders, and processing/verifying electronic transactions. Personal interaction with a teller, or even visits to a bank ATM will become obsolete. All one will have to do is turn on his computer.
CONCLUSION
In this , we realize a fair electronic cash system by using a verifiable encryption in the payment phase. The customer can keep his privacy, and his identity will not be traced by anyone if he does not spend his coins twice. By using a non-interactive proof and three sub-protocols of fair exchange, the customer and the merchant canfairly exchange their coins and goods. Nobody can gain an advantage in the exchange. But we have to say with regret that our scheme has high computational costs; we are investigating how to reduce the computation complexity in the future.