  Auditing provides an essential security control in computer systems, by
keeping track of all access attempts, including both legitimate and illegal
access attempts. This phase can be useful to the context of audits, where
eventual misbehaving parties can be held accountable. Blockchain technology can
provide trusted auditability required for access control systems. In this
paper, we propose a distributed \ac{ABAC} system based on blockchain to provide
trusted auditing of access attempts. Besides auditability, our system presents
a level of transparency that both access requestors and resource owners can
benefit from it. We present a system architecture with an implementation based
on Hyperledger Fabric, achieving high efficiency and low computational
overhead. The proposed solution is validated through a use case of independent
digital libraries. Detailed performance analysis of our implementation is
presented, taking into account different consensus mechanisms and databases.
The experimental evaluation shows that our presented system can process 5,000
access control requests with the send rate of 200 per second and a latency of
0.3 seconds.
