Fighting the Problem of Unsolicited E-Mail Using a Hashcash Proof-of-Work Approach

Abstract

This chapter investigates the problem of e-mail spam, and identifies methods to minimize the volumes. The analysis focuses on the hashcash proof-of-work approach, and investigates the feasibility of a hashcash-based solution. A potential problem with proof-of-work is that disparity across different powered computers may result in some unfortunate users spending a disproportionately long time calculating a stamp. An experiment is carried out to time how long it takes to calculate stamps across a variety of processor speeds. It is concluded from the analysis of the results that due to this problem of egalitarianism, hashcash (or CPU-bound proof-of-work in general) is not a suitable approach as a stand-alone anti-spam solution. It appears that a hybrid anti-spam system in conjunction with a legal and policy framework is the best approach.