A method of providing access to securely held data is provided. A user interacts with the service provider to obtain access to a service by using a device to provide a digital identifier to the service provider, without the digital identifier being made known to the user. At a later date the user wishes to retrieve securely stored data relating to their use of the service. However, because the user does not know the digital identifier, they are unable to identify themselves to the service provider using the digital identifier. The present disclosure provides a secure method for exchanging private identifiers, which allows the user to identify themselves to the service provider in order to gain access to securely stored data relating to the user's previous use of the service. The user can do this using the device on which the digital identifier is stored, or another device.