Title:             Universally Composable and Privacy-Preserving Audit Logs Using Bulletin Board
Authors:           Jan Camenisch; Manu Drijvers; Maria Dubovitskaya; Anna Kaplan
Key words:         universally composable, privacy-preserving, audit logs, bulletin board

Abstract:
Audit logs keep record of financial transactions and when being asked for
financial details, companies and banks will show their audit logs to convince
auditors of their financial situation. The auditor in all cases should neither
be able to be fooled by wrong audit logs nor should there be several audit
trails for one audited user. Putting audit logs onto blockchain setting makes
forging audit logs impossible due to the tamper-proof nature of blockchain.
Unfortunately, most blockchains handle their data in a transparent way and due
to the very sensible nature of audit logs, this is not acceptable.

In this paper, we will design a solution to put audit logs on a blockchain in
a privacy-preserving way. This will be done in the framework of Extended
Universal Composability, with the help of a global clock ideal functionality
and a bulletin board functionality. We will propose a generic construction for
our audit log ideal functionality. A proof of concept of our construction is
given for the Hyperledger Fabric blockchain.