数字现金是电子货币的一种形式。

Digital cash is one example of digital currency.

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通过在线交易，用户将现金兑换为虚拟货币，并将其储存在“电子钱包”中。

Users swap cash for virtual currency using online exchanges, then store it in a wallet program on their computer.

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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。

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

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