In the spread of electronic commerce such as an electoronic auction, an
electronic mall through Internet, the most important benefit of
electoronic commerce is that anyone can join anywhere at
anytime. However, a user might been implicated in the crime, or information about a user gives might be disclosed or
disseminated by the transaction with a malicious users or
organization. Therefore, we propose schemes to prevent such problems as follows:
- Signature with a Guarantee
The most important benefit
of electronic commerce is that anyone can join from anywhere at
anytime. As a result, subjects with whom we make a contract have been
more scattered geographically over a wide and rapidly
spreaded. However, we have no way to verify the transaction with persons
or organizations which are unfamiliar to us. Therefore, we need
a signature scheme with a guarantee by other trustworty persons or
organizations to transact with unfamiliar
persons or organizations smoothly, through Internet.
In this paper, we propose a new concept of a signature scheme with a
guarantee, and propose a formal model and a basic scheme for it.
- Anonymous Credential System
As information gets increasingly accessible, it has been important that
individuals control their information to protect their privacy, even if
organizations which a user transacts team up.
Anonymous credential systems allow users to
work effectively and anonymously with multiple organizations by using different
pseudonyms. Such systems are called anonymous when transactions carried out by
the same user cannot be correlated. In the systems, an organization knows
users by only pseudonym in which each pseudonym cannot be
linked to others.
An organization issues a credential on a pseudonym, and the
corresponding user demonstrates the possession of this credential to another
organization without revealing anything but the possession.
In the previous schemes, however, proving the possession of a
credential gives a verifier the information about which
organization a user transacts with, unfortunately. As a result, this compromises
the privacy of users.
The best an anonymous credential system should be able to choose the level of
privacy according to its security policies.
In this paper, we propose an anonymity-enhanced pseudonym system by showing a
credential issued by a group.
Furthermore, showing of multiple credentials needs much computational
and communication cost. In this paper, we propose an
efficient credential system which allows users to show
multiple credentials
- Proxy-bidding
The most common auction style is the open-bid English auction. Bidders
are required to be watching the current prices, and it usually takes a
long time to close the auction. The proxy-bidding system is a method
whereby a bidder asks proxy to go to the auction and bid on
himself. Such a system makes bidding on auctions more convenient and
less time consuming for bidders, is becoming popular in Internet. In
this paper, we propose an efficient and safety proxy-bidding.
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