Patent ID: 7505944

Claim:
A method of offline payment, comprising: calculating a first authentication code based on a payment amount and a secret verification key; calculating a commitment value by an electronic check medium, having a memory and an integrated circuit residing thereon, calculating the commitment value including calculating the commitment value based on the first authentication code and a secret key; communicating the commitment value to a terminal configured to receive a payment from the electronic check medium; determining a random/pseudo-random value by the terminal in response to receiving at least the commitment value, the random/pseudo-random value being configured to verify that the electronic check medium is authentic; communicating the random/pseudo-random value to the electronic check medium determining a second authentication code by the electronic check medium, the second authentication code being based on the random/pseudo-random value; communicating the second authentication code to the terminal; verifying the received second authentication code by comparing the second authentication code with the random/pseudo-random value; and accepting payment from the electronic check medium in response to verifying the second authentication code.