syssec_red_book

7 Authentication and AuthorizationHaving achieved personalization at an unprecedented scale, currentservices offer specialized content according to their users’ preferences.Using a web site or a mobile application, in the majority ofcases, requires creating a user account and authenticating with the providedservice at a later time. Authentication is carried out by providing the correctcredentials, usually expressed in the form of a username and a text-basedpassword. Password-based authentication is the de facto method of accesscontrol in web services as it is cheap and simple in principle. However, the wayusers choose and services manage passwords may expose them to attacks [130].A simple password is more convenient for users to remember; however, a simplepassword or its permutation is also more likely to be included in a worddictionary used in guessing attacks. Even if users select complex passwords,security pitfalls in the way services manage authentication credentials couldlead to leaks, often on a massive scale [26, 50, 59, 61].A common mitigation of such leaks is storing the output of one-way hashfunctions instead of the password itself, although this is not a practice followedby everyone [29]. Nevertheless, modern hardware enables powerful passwordcrackingplatforms [60, 234] that can reveal the input that generated a givenpassword digest. Aided by a dictionary and following certain assumptionsthat optimize the process, such systems feed a large number of possible inputsto the hash function in a rapid fashion. Furthermore, passwords can be alsoobtained by malware and social engineering attacks such as phishing [153].This problem is only exacerbated by the fact that users reuse passwordsacross services [189] which means that domino-like attacks could be carriedout [52, 56, 126].While researchers have argued that passwordsare not by any means the most valuable asset incybercrime [182], password theft can cause annoyance,financial damages, data loss, and loss of privacy[199,212]. It comes as no surprise that there is astrong push to replace passwords [23, 42, 129]. Somemechanisms that offer an alternative to textual pass-