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A PDA Implementation of an Off-line e-Cash Protocol PowerPoint Presentation
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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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Presentation Transcript
features of the standard cash
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

All transactions must be performed personally

Features of the Standard Cash
credit debit cards features
Credit/Debit Cards:

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 required

Credit/Debit Cards Features
alternative e cash
Goals

To substitute standard banknotes

To provide more flexibility than credit/debit cards

Requirements

anonymity

Non-traceable protocols

fairness

divisibility

transferability

Off-line protocols

accountability

Alternative: E-cash
e cash previous works 1 2
In 1982, David Chaum proposed a way to make electronic payments anonymously, introducing the concept of e-cash.

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)
e cash previous works 2 2
In 1993, S. Brands proposed a new protocol, whose security lies in the Schnorr digital signatures and prime finite field arithmetic.

In 1996, Frankel, Tsiounnis and Yung [11], [12] 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)
model and protocols
Our system consists of four entities, namely,

The Bank.

The Purchaser;

The Store;

The Authority

And the scheme consists of five sub-protocols:

Initialization Process

Withdrawing protocol

Payment/purchasing protocol

Deposit/collection protocol

Owner/coin tracing protocol

Model and Protocols
coin generation
Coin Generation
  • A coin is represented as a six-tuple:
  • {A, B, z, a, b, r}, Where:
  • A, B contain user information (encrypted)
  • z, a, b contain coin information required
  • for verification (encrypted)
  • r Bank signature (under the Schnorr scheme)
conclusion
We present the implementation of a fair e-cash protocol especially designed for mobile wireless environments, with the following features:

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