User authentication to a server is typically done by present- ing a username and a password in some protected form to the server, and having the server verify that those credentials correspond to an iden- tity previously registered and authorized for access. It is crucial that attackers never get access to operational passwords, which typically is achieved by encryption in transit, or through a challenge-response pro- tocol between the client and server computer platforms. However, these mechanisms do not protect passwords at the moment when they are en- tered into the client computer, which leaves the password exposed to attacks by malware on the client. We present a method for protecting passwords from being exposed on client platforms. The method is an extension of the well-known HTTP Digest Access Authentication which is a challenge-response protocol specified as part of HTTP. The method relies on an externalmostly offline personal authentication device called OffPAD which communicates with the client platform. We show how the presented authentication scheme increases security as well as enhances usability with regard to identity management. In addition to describing the OffPAD device, we argue that the HTTP Digest Access Authenti- cation standard does not conform to today's best practices, and suggest improvements.
['Henning Klevjer', 'Kent Are Varmedal', 'Audun Jøsang']
Extended HTTP Digest Access Authentication