What are Indexed TAN Lists?
In a conventional Transaction Authentication Number (“TAN”) system, the user is requested to provide an arbitrary TAN number he previously received as a random list from the corporation for validation of future transactions. Afterwards, this TAN is marked as used by the system and cannot be reused. An Indexed TAN list represents a more secure system. When the user wants to validate a transaction, the server requests a specific unused TAN from the list according to the index. This makes that particular TAN number bound to a specific transaction and the number cannot be used for another transaction.
