2020/02/04 by Benjamin Harsha, Robert Morton, Robert A. Morton +8 · 1 voice
Computer Science · Social Sciences · #User Authentication and Security Systems #Advanced Malware Detection Techniques #Privacy, Security, and Data Protection
paper · pdf · doi:10.48550/arxiv.2002.01513
We examine the issue of password length leakage via encrypted traffic i.e.,\nbicycle attacks. We aim to quantify both the prevalence of password length\nleakage bugs as well as the potential harm to users. In an observational study,\nwe find that em most of the Alexa top 100 rates sites are vulnerable to\nbicycle attacks meaning that an eavesdropping attacker can infer the exact\nlength of a password based on the length the encrypted packet containing the\npassword. We discuss several ways in which an eavesdropping attacker could link\nthis password length with a particular user account e.g., a targeted campaign\nagainst a smaller group of users or via DNS hijacking for larger scale\ncampaigns. We next use a decision-theoretic model to quantify the extent to\nwhich password length leakage might help an attacker to crack user passwords.\nIn our analysis, we consider three different levels of password attackers:\nhacker, criminal and nation-state. In all cases, we find that such an attacker\nwho knows the length of each user password gains a significant advantage over\none without knowing the password length. As part of this analysis, we also\nrelease a new differentially private password frequency dataset from the 2016\nLinkedIn breach using a differentially private algorithm of Blocki et al. (NDSS\n2016) to protect user accounts. The LinkedIn frequency corpus is based on over\n170 million passwords making it the largest frequency corpus publicly available\nto password researchers. While the defense against bicycle attacks is\nstraightforward (i.e., ensure that passwords are always padded before\nencryption), we discuss several practical challenges organizations may face\nwhen attempting to patch this vulnerability. We advocate for a new W3C standard\non how password fields are handled which would effectively eliminate most\ninstances of password length leakage.\n