(6)In order to ensure the application of strong customer authentication, it is also necessary to require adequate security features for the elements of strong customer authentication categorised as ‘knowledge’ (something only the user knows), such as length or complexity, for the elements categorised as ‘possession’ (something only the user possesses), such as algorithm specifications, key length and information entropy, and for the devices and software that read elements categorised as ‘inherence’ (something the user is) such as algorithm specifications, biometric sensor and template protection features, in particular to mitigate the risk that those elements are uncovered, disclosed to and used by unauthorised parties. It is also necessary to lay down the requirements to ensure that those elements are independent, so that the breach of one does not compromise the reliability of the others, in particular when any of these elements are used through a multi-purpose device,namely a device such as a tablet or a mobile phone which can be used both for giving the instruction to make the payment and in the authentication process.