The growth of shared Wi-Fi and other wireless computer networks has increased the risk of eavesdropping on Internet communications, but researchers at Carnegie Mellon University have devised a low-cost system that can thwart these “Man-in-the-Middle” (MitM) attacks.

The system, called Perspectives, also can protect against attacks related to a recently disclosed software flaw in the Domain Name System (DNS), the Internet phone book used to route messages between computers.

The researchers — David Andersen, assistant professor of computer science, Adrian Perrig, associate professor of electrical and computer engineering and public policy, and Dan Wendlandt, a Ph.D. student in computer science — have incorporated Perspectives into an extension for the popular Mozilla Firefox v3 browser than can be downloaded free of charge.

Perspectives employs a set of friendly sites, or “notaries,” that can aid in authenticating Web sites for financial services, online retailers and other transactions requiring secure communications. By independently querying the desired target site, the notaries can check whether each is receiving the same authentication information (a digital certificate), in response. If one or more notaries report authentication information that is different than that received by the browser or other notaries, a computer user would have reason to suspect that an attacker has compromised the connection.

Certificate authorities, such as VeriSign, Comodo and GoDaddy, already help authenticate Web sites and reduce the risk of MitM attacks. The Perspectives system provides an extra measure of security in those cases but will be especially useful for the growing number of sites that do not use certificate authorities and instead use less expensive “self-signed” certificates.