syssec_red_book

7. Authentication and Authorizationprovider. One of the benefits over OpenID and Facebook Connect is that theidentity provider (e-mail provider) does not find out which web service theuser is trying to use. On the other hand, while the identity provider does notlearn the relaying party, the relaying party learns the user’s identity on theidentity provider’s service; i.e., his e-mail address. PseudoID [152] employsblind cryptographic signatures to eliminate this privacy concern. Moreover,while Facebook Connect and Google Login associate the user with a socialprofile and may share some of that information with the third-party webservice, BrowserID does not. While BrowserID and Facebook Connect seemto eliminate the need for web services to maintain and manage the securitycredentials for their users, they also present single points of failure that, ifabused could result in domino-like security failures. For instance, a user whohas enabled Facebook Connect to log in to a plethora of web services, he onlyneeds to manage the Facebook password. However, if the same passwordis also used for another service that does not support Facebook Connect, apotential leak from either Facebook or that service could allow an attackeraccess to all the services connected to that user’s Facebook identity. Anotherexample, is the case where security flaws in the single-sign-on system enablean attacker to access the victim’s account in any of the services supportingsuch password-less login [391].7.5.2 Password CrackingPassword cracking is not a new technique [344]. However, up until recently,the use of cryptographic hash functions in the way authentication informationwas handled by services appeared as an effective defense. This is no longerthe case since modern CPUs/GPUs [60] can be combined to form powerfulcracking platforms targeting password digests. Many of them, such as Cloud-Cracker, are provided as an off-the-shelf paid service for the average user [9].Even if strong cryptographic hash functions are used for keeping passwordssafe, other properties of the system may be exploited to boost the processof cracking [12]. Research efforts have been directed towards suggestingharder-to-guess passwords and pass-phrases [234, 322, 396].7.5.3 Adaptive HashingAdaptive cryptographic hash functions, such as bcrypt [323] and scrypt [313],have been proposed to address the increasing ease with which passwordhashes can be cracked. These hash functions can adapt to hardware evolution,by deliberately wasting resources - either computational or memory - duringa hash validation. By employing such hash functions, a web site can slowdown an attacker sufficiently in cracking a particular user password. However,this also requires that the service invests additional resources into generating56