Derive a new password from a master password in a way that can be repeated.
You should never use the same password for more than one website, and that's why you should use a password manager. If you can't, then you should write your passwords in a notebook (it's still better than reusing passwords).
What you probably shouldn't do is to use this key derivation tool. In theory it's still better than reusing the same password, but this tool has not been written nor reviewed by a professional security expert.
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