Security researcher Troy Hunt this week announced his new version of "Pwned Passwords," a search tool and list of more than 500 million passwords that have been leaked in data breaches. Users can access it online and developers can connect applications to it via an API.
Within a day, the company AgileBits had integrated Hunt's new tool into the 1Password password manager. AgileBits' announcement describes how it works:
Customers with 1Password.com accounts can already use the tool in a Web browser. You'll need to input "Shift-Control-Option-C (or Shift+Ctrl+Alt+C on Windows) to unlock the proof of concept." After that, a "Check Password" button will appear next to your passwords.
Troy's new service allows us to check your passwords while keeping them safe and secure. They're never sent to us or his service.
First, 1Password hashes your password using SHA-1. But sending that full SHA-1 hash to the server would provide too much information and could allow someone to reconstruct your original password. Instead, Troy's new service only requires the first five characters of the 40-character hash.
To complete the process, the server sends back a list of leaked password hashes that start with those same five characters. 1Password then compares this list locally to see if it contains the full hash of your password. If there is a match then we know this password is known and should be changed.
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