Off-line 'anonymous' electronic money
In the make use of off-line electronic money, the merchant does not require to cooperate with the bank before tolerant a coin from the user. As a substitute he can collect multiple coins useless by users and put them later with the bank. In principle this could be done off-line, i.e. the mercantile could go to the bank with his storage media to replace e-cash for cash. However the merchant is certain that the user's e-coin will either be established by the bank or the bank will be able to recognize and punish the cheating user. In this way a user is prohibited from spending the similar coin twice (double-spending). Off-line e-cash schemes as well need to guard against cheating merchants, i.e. merchants that want to set down a coin twice (and then blame the user).
By cryptography, anonymous e-cash was established by David Chaum. He used blind signatures to get unlink ability between withdrawal and spend transactions. In cryptography, e-cash typically refers to anonymous e-cash. Depending on the assets of the payment transactions, one distinguishes between on-line and off-line e-cash. The first off-line e-cash system was planned by Chaum and Naor. Like the first on-line scheme, it is based on RSA sightless signatures.