  Access control is a fundamental component of the design of distributed
ledgers, influencing many aspects of their design, such as fairness,
efficiency, traditional notions of network security, and adversarial attacks
such as Denial-of-Service (DoS) attacks. In this work, we consider the security
of a recently proposed access control protocol for Directed Acyclic Graph-based
distributed ledgers. We present a number of attack scenarios and potential
vulnerabilities of the protocol and introduce a number of additional features
which enhance its resilience. Specifically, a blacklisting algorithm, which is
based on a reputation-weighted threshold, is introduced to handle both spamming
and multi-rate malicious attackers. The introduction of a solidification
request component is also introduced to ensure the fairness and consistency of
network in the presence of attacks. Finally, a timestamp component is also
introduced to maintain the consistency of the network in the presence of
multi-rate attackers. Simulations to illustrate the efficacy and robustness of
the revised protocol are also described.
