PayPal is a possible funding source for ecash/estamps/remailer-tokens or whatever. With a PayPal account you can receive funds and pay people, two elementary steps for a cash-based system. It is easy to set up web software to receive payment via PayPal, and many people are already in the system (it is the most widely used payment system for eBay). Payments either go through the credit card clearing houses or via PayPal itself, but merchants don't have to be aware of the difference, except for the danger of reversed transactions. There are plenty of horror stories on the web about PayPal, from such sites as www.paypalsucks.com and www.paypalwarning.com. Probably some fraction of these are from pissed off scammers who got caught. There appears to be a specific problem in the PayPal terms of service: 13. No Cash Advances. You agree not to engage in behavior that could reasonably be construed as providing yourself a cash advance from your credit card, and agree not to assist Users who engage in behavior that could reasonably be construed as providing themselves a cash advance from their credit cards. Such behavior includes, but is not limited to, a User paying someone with a credit card-funded payment through the Service, then receiving the funds back from the original Recipient and attempting to withdraw the funds from their account. PayPal reserves the right to reverse all such transactions and to terminate any accounts that are associated with such behavior. This kind of transaction could easily happen with an ecash-selling service, if the ecash can be redeemed via PayPal. Someone buys some ecash with a credit card, cashes in the ecash for funds in his PayPal account, and then withdraws the funds. This would be an express violation of the PayPal terms of service. Besides this problem, there is the danger of reversed transactions. Someone who buys ecash with a credit card can cancel the transaction for any of several reasons, such as claiming that it was done via a stolen credit card. In that case PayPal makes the merchant (the ecash bank) take the loss. A competing service from Citibank is www.c2it.com. It is relatively new and does not have all of the conditions and limitations that PayPal does. The terms of service appear to be relatively generous. Citibank is a big company so one might hope that they have gone over the bases. Still it is possible that if C2It catches on that Citibank will eventually be forced to put in the same kinds of limitations that PayPal has. C2It also seems to be more oriented towards email and may not have the shopping cart software that PayPal provides. That could make it harder to interface to C2It from a script. Buying ecash will require at least one data exchange for supplying blinded data and receiving coins, independent of how the ecash is paid for. If that data exchange is separate from the email-based C2It payment transaction then there has to be some key to link them together. That will complicate the process and introduce new possibilities for error.