No abstract

No abstract

Abstract-Today's Internet services rely heavily on text-based passwords for user authentication. The pervasiveness of these services coupled with the difficulty of remembering large numbers of secure passwords tempts users to reuse passwords at multiple sites. In this paper, we investigate for the first time how an attacker can leverage a known password from one site to more easily guess that user's password at other sites. We study several hundred thousand leaked passwords from eleven web sites and conduct a user survey on password reuse; we estimate that 43-51% of users reuse the same password across multiple sites. We further identify a few simple tricks users often employ to transform a basic password between sites which can be used by an attacker to make password guessing vastly easier. We develop the first cross-site password-guessing algorithm, which is able to guess 30% of transformed passwords within 100 attempts compared to just 14% for a standard password-guessing algorithm without cross-site password knowledge.

Quite often on the Internet, cryptography is used to protect private, personal communications. However, most commonly, systems such as PGP are used, which use long-lived encryption keys (subject to compromise) for confidentiality, and digital signatures (which provide strong, and in some jurisdictions, legal, proof of authorship) for authenticity.In this paper, we argue that most social communications online should have just the opposite of the above two properties; namely, they should have perfect forward secrecy and repudiability. We present a protocol for secure online communication, called "off-the-record messaging", which has properties better-suited for casual conversation than do systems like PGP or S/MIME. We also present an implementation of off-the-record messaging as a plugin to the Linux GAIM instant messaging client. Finally, we discuss how to achieve similar privacy for high-latency communications such as email.