Patent ID: 7747539

Claim:
A method of processing a financial transaction initiated by a consumer with a contactless transaction device, the method comprising: receiving a first electromagnetic transmission from the contactless transaction device, the first electromagnetic transmission providing an identification of a financial account and an adjunct identifier; electromagnetically transmitting transaction data defining aspects of the financial transaction to the contactless transaction device; receiving a second electromagnetic transmission from the contactless transaction device, the second electromagnetic transmission providing authentication data and a digital signature originated from the transaction data through application of a cryptographic key maintained on the contactless transaction device; authenticating the contactless transaction device with an analysis of the authentication data and digital signature; transmitting an authorization request for approval of the financial transaction over a payment network to an issuer system maintained by or on behalf of an issuer who maintains the financial account; receiving a response to the authorization request from the issuer system; transmitting the adjunct identifier to an adjunct system distinct from the issuer system for implementation of functions adjunct to the financial transaction; and acting on the financial transaction in accordance with the response to the authorization request; wherein the authentication data comprises a pattern resulting from application of a hashing algorithm to the transaction data; the cryptographic key is a private key of an asymmetric-cryptography public-key-private-key pair; the digital signature comprises a result of encrypting the pattern with the private key; and authenticating the contactless transaction device comprises: applying the hashing algorithm to the transaction data to calculate a comparison hash value; decrypting the digital signature with the public key; and comparing the decrypted digital signature with the comparison hash value.