Cure for Spam Over Internet Telephony

Unsolicited bulk email or spam is a menace to the usability of Internet email. The possibility of cheap Voice over IP (VoIP) services have introduced the threat of Spam over Internet Telephony (SPIT). A previously unexperimented solution for tackling the spam machinery is to increase its cost via Human Interactive Proofs (HIP). These proofs are basically applicable to all kind of spam, including email, but we concentrate on the Session Initiation Protocol (SIP) in this paper. Our approach allows the use of varying kinds of HIPs to prevent automated call connection attempts. The HIPs are used as an enrollment feature for configuring the call-recipient's call pass or block lists. By giving a proof of humanity, the caller is automatically put e.g. to the call-recipient's graylist for further processing by the user. The approach can be also used to mitigate unsolicited call connection attempts made by humans. We also present our SIP signaling based solution to address the SPIT threat.