Patent ID: 7155418

Claim:
A method of transferring electronic cash from first user device to a second user device, said method comprising: mutually authenticating the first user device and the second user device; sharing a temporary key between the first user device and the second user device; appending, at the first user device, a signature associated with the first user device to a monetary amount of electronic cash that is to be transferred from the first user device to the second user device; encrypting, at the first user device, the transfer monetary amount of electronic cash and the appended signature associated with the first user device using the temporary key; transmitting, from the first user device to the second user device, the encrypted transfer monetary amount of electronic cash and the encrypted signature associated with the first user device; decrypting, at the second user device, the encrypted transfer monetary amount of electronic cash and the encrypted signature associated with the first user device using the temporary key; adding, at the second user device, the transfer monetary amount of electronic cash to a stored monetary amount of electronic cash associated with the second user device; appending, at the second user device, a signature associated with the second user device to the transfer monetary amount of electronic cash; encrypting, at the second user device, the transfer monetary amount of electronic cash and the appended signature associated with the second user device using the temporary key; transmitting, from the second user device to the first user device, the encrypted transfer monetary amount of electronic cash and the encrypted signature associated with the second user device; decrypting, at the first user device, the encrypted transfer monetary amount of electronic cash and the encrypted signature associated with the second user device using the temporary key; and subtracting, at the first user device, the transfer monetary amount of electronic cash from a stored monetary amount of electronic cash associated with the first user device.