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Comment by aba_sababa | Hacker News Reader

As opposed to a password manager, where it's trivial to know every password within if you know the master password?

Getting the master password, itself, need not be trivial. Mine is in my head and in my wallet. And, even if you happen to stumble across one of my passwords, you can't derive any other passwords from it.

Well, the difference is that if I compromise any of the sites you use, I now know all your passwords. If I compromise any of the sites you use when you use a password manager properly, I'll only know one password that'll be fairly useless to me.

Compromising one of these passwords does not at all mean that all the other passwords are compromised. You can't figure out the original master password from a hashed, compromised password.

Yes, you can. To understand why, compare:

This:

  'facebook' + 'mypassword'
  'twitter' + 'mypassword'
  'foursquare' + 'mypassword'

Password manager with unique passwords:

  'mSX32ZyKZXptY3E'
  '33RiKbc3n6sA6IY'
  '4kGzFtWDd0rnti6'

All I have to do is figure out what you named the site that I compromised, then do exactly what I'd usually do to recover your password, and, voila, I can now access all sites you use it for. Compare this to the password manager example where each password has been generated at random--one password communicates no information whatsoever about the other.

Ok, so you know that "facebook" is part of the original hash. Not following how you can also derive "mypassword" from it. If you have a good strong master password, rainbow tables won't be able to crack the hash.

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