In cryptocurrency-based permissionless blockchain networks, the decentralized
structure enables any user to join and operate across different regions. The
criminal entities exploit it by using cryptocurrency transactions on the
blockchain to facilitate activities such as money laundering, gambling, and
ransomware attacks. In recent times, different machine learning-based
techniques can detect such criminal elements based on blockchain transaction
data. However, there is no provision within the blockchain to deal with such
elements. We propose a reputation-based methodology for response to the users
detected carrying out the aforementioned illicit activities. We select Algorand
blockchain to implement our methodology by incorporating it within the
consensus protocol. The theoretical results obtained prove the restriction and
exclusion of criminal elements through block proposal rejection and attenuation
of the voting power as a validator for such entities. Further, we analyze the
efficacy of our method and show that it puts no additional strain on the
communication resources.