A PDA Implementation of an Off-line e-Cash Protocol. E-cash basic definitions. Banknotes: Provides anonymity They are valid virtually everywhere The legitimate owner is the one who carries them Portability of great amounts of money is difficult/risky
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transactions of big quantities of money are possible
They are portable and secure →People trust them.
Electronic transactions are possible
They can be used for getting banknotes
A legitimate owner must authenticate him/herself
They do not provide anonymity
The Bank must authorize the transaction via electronic connection → on-line protocols are requiredCredit/Debit Cards Features
However the main drawback of the e-cash concept is that electronic money could be copied and reused (double spending problem).
In ‘88, Chaum, Fiat and Naor proposed an off-line protocol.
In ’91, Okamoto and Otha proposed that an ideal e-cash system should have the following properties: independence, security, privacy, off-line payment, transferability, divisibility.E-cash: Previous Works (1/2)
In 1996, Frankel, Tsiounnis and Yung ,  proposed the concept of Fair Off-line e-Cash. There, an entity called the Authority was used to guarantee the anonymity of a purchaser as long as he/she makes legal transactions. If a purchaser tries to commit fraud, the Bank could request the tracing of a coin or the tracing of the owner of a coin.
Many other systems have been proposed recently…E-cash: Previous Works (2/2)
Our protocol attempts to offer a reasonable balance between anonymity; and the possibility of revoking that anonymity under special circumstances.
For that, our system considers two protocols especially designed for tracing purposes: a coin tracing and an owner tracing protocol;
Our system was written in Java and it was implemented in a wireless environment with PDA mobile devices.Conclusion