Spam control by source throttling using integer factorization

Spam has become major concern for the Internet provider in modern era. The key reason for the growth of spam is the fact that it costs nothing to send an email; since all of the costs are paid by the carriers and the email servers. Existing solutions for spam control are strictly limited to spam filtering at the receiver side, but these solutions underestimate the fact that network bandwidth and processing time of the recipient email servers are wasted. To cut down these costs spam should be stopped before it reaches receiving email server. In this paper, we propose a solution to control spam at senders email server by throttling the client´s CPU using integer factorization problem. Integer factorization is used to generate stamps as a proof of CPU cycles expended by the senders system for each email recipient. Cost of generating stamps is negligible when the client is sending email to few recipients. However, as the number of recipients increases, the cost of generating stamp also increases which adversely affects the processing speed of the client. The server requires minimal processing time to verify stamps generated by the client. By enforcing the client to generate a valid stamp, the proposed solution discourages the spammer to misuse the available bandwidth for sending spam.