> Chaum published the idea of anonymous electronic money in a 1983 paper;[1] eCash software on the user's local computer stored money in a digital format, cryptographically signed by a bank. The user could spend the digital money at any shop accepting eCash, without having to open an account with the vendor first, or transmitting credit card numbers. Security was ensured by public key digital signature schemes. The RSA blind signatures achieved unlinkability between withdrawal and spend transactions. Depending on the payment transactions, one distinguishes between on-line and off-line electronic cash: If the payee has to contact a third party (e.g., the bank or the credit-card company acting as an acquirer) before accepting a payment, the system is called an on-line system.[2] In 1990, Chaum together with Moni Naor proposed the first off-line e-cash system, which was also based on blind signatures.[3]

* https://en.wikipedia.org/wiki/Ecash