5 ms·

First of all, in an online brute forcing scenario attackers will never get through the entire 20 trillion. Even if they knew for certain that the target victim'

First of all, in an online brute forcing scenario attackers will never get through the entire 20 trillion. Even if they knew for certain that the target victim's password satisfied the precise constraints of the passwords published in that list, they'd need around 2 years (with reasonable assumptions of millisecond latency) of constant, 24/7 attempts to run through them all. This is assuming there is no rate limiting. In an offline brute forcing scenario, either the passwords have been hashed with a strong key derivation function and a randomized salt or they haven't. If they have, it doesn't matter if the password is in that list. If they haven't, you're most likely screwed either way, because attackers can get up to 1 trillion password attempts per second in real world cracking setups now.

geofft 8y ago
No, you're not screwed either way, because there are trillions of trillions of trillions of possible 20-character passwords. So even if they can get one trillion attempts per second, it will still take an attacker trillions of trillions of seconds to brute-force all possible 20-character passwords, which is longer than the lifetime of the universe.
- throwawaymath 8y ago
  Now keep in mind that 1) it is possible to choose a strong password with fewer than 20 characters, and 2) most people will not choose a password that long. Extrapolating further, this "policy" would disallow people from choosing passwords below a certain length, because it's theoretically plausible someone has published the set of all possible strings fewer than n characters long.
  - deleted 8y ago
    [deleted]
  - geofft 8y ago
    > Extrapolating further, this "policy" would disallow people from choosing passwords below a certain length, because it's theoretically plausible someone has published the set of all possible strings fewer than n characters long. Yes, that seems like a good password policy. A list of possible alphanumeric strings that is actually reasonable to physically publish (i.e., not 20 trillion) is a list of extremely short alphanumeric strings. 5 alphanumeric characters is 380 million possible strings. 6 is about 2 billion. You should absolutely ban passwords that are 6 characters or shorter! In fact, I would go so far as to say that the questions of "Is this password too short because someone could brute-force all the possibilities, even if we're using a good password hash and a previously-unknown salt" and "Can someone physically enumerate all passwords of this size and put them on Pastebin or otherwise get them in the HIBP database" are equivalent.
    - throwawaymath 8y ago
      Salts do not need to be previously unknown. This goes back to what I was saying - they're either securely protected with a key derivation function, or they're not.
      - Dylan16807 8y ago
        Right. That was just to give the most generous possible circumstances to a password when arguing that it's still too weak.

geofft 8y ago

No, you're not screwed either way, because there are trillions of trillions of trillions of possible 20-character passwords. So even if they can get one trillion attempts per second, it will still take an attacker trillions of trillions of seconds to brute-force all possible 20-character passwords, which is longer than the lifetime of the universe.

throwawaymath 8y ago
Now keep in mind that 1) it is possible to choose a strong password with fewer than 20 characters, and 2) most people will not choose a password that long. Extrapolating further, this "policy" would disallow people from choosing passwords below a certain length, because it's theoretically plausible someone has published the set of all possible strings fewer than n characters long.
- deleted 8y ago
  [deleted]
- geofft 8y ago
  > Extrapolating further, this "policy" would disallow people from choosing passwords below a certain length, because it's theoretically plausible someone has published the set of all possible strings fewer than n characters long. Yes, that seems like a good password policy. A list of possible alphanumeric strings that is actually reasonable to physically publish (i.e., not 20 trillion) is a list of extremely short alphanumeric strings. 5 alphanumeric characters is 380 million possible strings. 6 is about 2 billion. You should absolutely ban passwords that are 6 characters or shorter! In fact, I would go so far as to say that the questions of "Is this password too short because someone could brute-force all the possibilities, even if we're using a good password hash and a previously-unknown salt" and "Can someone physically enumerate all passwords of this size and put them on Pastebin or otherwise get them in the HIBP database" are equivalent.
  - throwawaymath 8y ago
    Salts do not need to be previously unknown. This goes back to what I was saying - they're either securely protected with a key derivation function, or they're not.
    - Dylan16807 8y ago
      Right. That was just to give the most generous possible circumstances to a password when arguing that it's still too weak.