It is said, a combination of What you have (a smart card), what you know (a PIN) and what you are (biometric - fingerprint, iris, palm vein, etc.) with adequate security gives unique identity to every person and every transaction, thereby making it tamper proof.

The transactions can be stored in a central server and cannot be accessed by any unauthorized person if proper security measures are built-in. The individual can have a complete record of transactions in his/her smart card and is fool proof as it is done using biometric and PIN.

This can give the necessary anonymity and yet full security against repudiation.