Universally Composable Security Analysis of OAuth v2.0

This paper defines an ideal functionality for delegation of web access to a third-party where the authentication mechanism is password-based. We give a universally-composable (UC) realization of this ideal functionality assuming the availability of an SSL-like ideal functionality. We also show that this implementation can be further refined to give a browser based implementation whenever the browser supports https redirection. This implementation matches the ’Authorization Code’ mode of the OAuth Version 2.0 Internet draft proposal, with the additional requirement that the third-party along with the Authorization Server must support an SSL-like functionality. From the universally-composable perspective, our ideal functionality definition is novel in the respect that it does not require the three parties to decide on a session identifier in advance, which is usually assumed in a UC setting. This allows us to realize the ideal functionality without any wrapper code, and thus exactly matching the desired protocol in the OAuth standard.