The invention provides a method and system for providing financial details from a mobile device of a user for use in a transaction. The method is performed on a mobile device of the user and includes the steps of generating, on a token generating component, a session-specific token by applying an algorithm requiring a dynamic key; providing financial details for use in a transaction; incorporating the session-specific token and the financial details into a modified form the financial details; and transferring the modified form of the financial details from the mobile device to initiate the transaction. A corresponding method and system for validating financial details received, at a server of an issuing authority, is also provided.