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If there's generic malware that's targeting your password manager, then yes this provides protection against that. But it doesn't provide protection against a targeted attack, because the malware can just keylog your horcrux. Another weakness that doesn't require a keylogger, is the attacker might be able to find some stolen database of a website that stored passwords in plaintext, then deduce your horcrux from the difference between what was in your password manager and what was in the database. And if the site did hash passwords, the attacker can try cracking the horcrux. The 5-character example horcrux probably wouldn't be too hard. The article somewhat covers this by saying only use the horcrux on important sites. This is good, but it still has weaknesses because an important site can still get its database stolen, and some people also want to protect less important sites. And if no password databases are available, the attacker can create a website and ask you to join it under the hope you'll reuse your horcrux on the attacker's site. I've actually had an attacker contact me personally (that is, actually chatting with me live) and ask me to sign up for his forum under the hope that I would reuse my valuable account's password on the forum. |
Some sites email your password to you: https://plaintextoffenders.com/