Protecting Poorly Chosen Secrets from Guessing Attacks

In a security system that allows people to choose their own passwords those people tend to choose passwords that can be easily guessed This weakness exists in practically all widely used systems Instead of forcing users to choose well chosen secrets which are likely to be di cult to remember we propose solutions that maintain both user convenience and a high level of security at the same time The basic idea is to ensure that data available to the attacker is su ciently unpredictable to prevent an o line veri cation of whether a guess is successful or not We examine common forms of guessing attacks develop examples of cryptographic protocols that are immune to such attacks and suggest a systematic way to examine protocols to detect vulnerabilities to such attacks