The Sibyl is a project invented and implemented by Pedro (pfortuny) and me (rafacas). Although I have to admit that it was Pedro's idea.
It started with the goal of secure storage of the shadow file and, in general, of any database of secret authentication tokens (think of passwords -actually hashes of passwords- of users of a Web-based service, for example). We consider it addresses the main concern on those databases: dictionary attacks and rainbow tables, which have become available at negligible cost: there is a cloud-based service for doing dictionary attacks on a WPA key.
Our approach for storing shadow files ...