To prevent e-cash from double-spending and unlimited increase in the records of databases, an improved offline e-cash system based on elliptic curve cryptography was proposed.

为防止电子现金重复花费和数据库记录无限制的膨胀问题，改进了现有的利用椭圆曲线密码系统构造的离线电子现金系统。

youdao

The double-spending is the kernel problem in the E-cash scheme, since the copying of E-cash is very easy.

由于电子货币容易被复制，所以防止电子现金的重复花费是设计电子现金方案必须考虑的安全问题。

youdao

In fact, in the first quarter, the growth in e-commerce spending was roughly double that observed at offline retail.

FORBES: ComScore: Consumers Spend $38 Billion Online in Q1