4 ms·

I agree, if you only pick words from the top 1000 most common english words it only takes 1000^4 = 1 trillion tries to crack a four words sentence. This is stil

I agree, if you only pick words from the top 1000 most common english words it only takes 1000^4 = 1 trillion tries to crack a four words sentence. This is still quite a lot but much more reasonable than cracking a 8 chars random password with brute force.

dllthomas 14y ago
He didn't compare to an 8 char random password. However, an 8 char random password is much harder to remember, and itself only contains (assuming 100 possible characters) only 10 quadrillion (or 53 bits) which is still somewhat weak. Including less common words, and using 5 of them, makes things significantly better. > grep '^[a-z]\+$' /usr/share/dict/words | wc -l gives 62887 on my system, which is almost 16 bits per word, so 4 puts us at over 63 bits and 5 at over 79 bits, or roughly 15 quintillion and 1 septillion respectively. Assuming brute force over sequences of words from the same dictionary and of the correct length, at a billion tries each second, it'll take over 200 years to crack the former and over 31 million years to crack the latter.
- laumars 14y ago
  Modern dictionary attacks use common terms that have been generated from analyzing the passwords that have been stolen from past attacks. So the dictionary isn't just a list of English words but in fact a catalog of terms that people do use for passwords in real life. This makes them much more effective than dictionary attacks off old.
  - dllthomas 14y ago
    Analyzing passwords that have been stolen helps you build a better dictionary. The math in the comic assumes an optimum dictionary has been constructed to attack this kind of password by inspecting the algorithm; no dictionary attack is going to do better than that without doing something like attacking the RNG used to generate the passwords (and if that's feasible you're just as vulnerable regardless of what approach you use).
    - laumars 14y ago
      While that is true, pen testers are still rattling off ~60% of passwords from dictionary attacks in just 3 weeks. This is why I would rather see emphasis placed on password length and irregularity than simply saying "memorable words can be secure", which is what most people will take away from that comic. So I was never arguing against passphrases per se. Though I appreciate I want very clear on that. (Like I said before, hangover + phone surfing != best platform for a complex discussion. :-)
      - dllthomas 14y ago
        Yes. Pen testers are rattling off the ~60% of passwords that were chosen poorly, all of which were chosen by methods other than the one detailed in the comic. Just placing an emphasis on password length and irregularity leaves people still with the question of how they generate that long, irregular password. Asking them to do it in their head in any way is going to lead to much success by way of dictionary attacks. I'm coming to the realization (giving you some credit) that your objection may be to a specific piece of the comic's particular presentation: "random" is often used to mean "arbitrary" and people might think they can do it in their head? Of course I agree that anything people do with their heads is almost certainly insecure - brains are piss-poor sources of entropy. Would your objection be fixed entirely if it called out explicitly that the words need to be picked mechanically (computer, dice, something) with a uniform distribution? Anyway, the thing that I like about the comic is that it presents a specific means of choosing a password that is simultaneously secure and memorable, and the only misconception involved would be from misinterpretation of the comic (which, as noted above, does seem possible). Anything else someone comes up with on their own is likely to be less secure, less memorable, or both, so referring to the comic as promulgating a misconception bugs me. Regarding the last, I don't think we were ever arguing about passphrases in general, but about a particular way of generating them... passphrase really just means "long password", more or less, and that doesn't provide a lot of guidance as to how to come up with one, and leaving people to their own devices is how we wind up with ~60% of passwords being horribly crackable.
        laumars 14y ago
- bnegreve 14y ago
  Yes, it's pretty secure against brute force. However if everyone start doing this, I suspect that we're going to have a lot of passwords like "I am hungry today" or even "car house hello red" which are both rather weak against an attack that would combine the most frequent words. You can't really prevent people from using common words and common patterns to build their password and hackers are going to use this fact. So my problem is that it gives the impression to be very secure whereas it's only secure under some conditions. (You have to pick words uniformly among the list of words.) Just like old password...
  - dllthomas 14y ago
    You have to pick the words uniformly, yes. Thankfully, that's easy to do (rl -c 4 wordfile), and can be made easier. The point isn't "make up passwords that look like this" - it's "using this algorithm you get passwords that look like this that have this level of security[1]," and it's way easier than generating a secure and memorable password by other means. [1] As I've said in a few places, the actual dictionary size and number of words should be tweaked to make the security level appropriate for your needs, which will vary by application and grow over time.

dllthomas 14y ago

He didn't compare to an 8 char random password. However, an 8 char random password is much harder to remember, and itself only contains (assuming 100 possible characters) only 10 quadrillion (or 53 bits) which is still somewhat weak. Including less common words, and using 5 of them, makes things significantly better. > grep '^[a-z]\+$' /usr/share/dict/words | wc -l gives 62887 on my system, which is almost 16 bits per word, so 4 puts us at over 63 bits and 5 at over 79 bits, or roughly 15 quintillion and 1 septillion respectively. Assuming brute force over sequences of words from the same dictionary and of the correct length, at a billion tries each second, it'll take over 200 years to crack the former and over 31 million years to crack the latter.

laumars 14y ago
Modern dictionary attacks use common terms that have been generated from analyzing the passwords that have been stolen from past attacks. So the dictionary isn't just a list of English words but in fact a catalog of terms that people do use for passwords in real life. This makes them much more effective than dictionary attacks off old.
- dllthomas 14y ago
  Analyzing passwords that have been stolen helps you build a better dictionary. The math in the comic assumes an optimum dictionary has been constructed to attack this kind of password by inspecting the algorithm; no dictionary attack is going to do better than that without doing something like attacking the RNG used to generate the passwords (and if that's feasible you're just as vulnerable regardless of what approach you use).
  - laumars 14y ago
    While that is true, pen testers are still rattling off ~60% of passwords from dictionary attacks in just 3 weeks. This is why I would rather see emphasis placed on password length and irregularity than simply saying "memorable words can be secure", which is what most people will take away from that comic. So I was never arguing against passphrases per se. Though I appreciate I want very clear on that. (Like I said before, hangover + phone surfing != best platform for a complex discussion. :-)
    - dllthomas 14y ago
      Yes. Pen testers are rattling off the ~60% of passwords that were chosen poorly, all of which were chosen by methods other than the one detailed in the comic. Just placing an emphasis on password length and irregularity leaves people still with the question of how they generate that long, irregular password. Asking them to do it in their head in any way is going to lead to much success by way of dictionary attacks. I'm coming to the realization (giving you some credit) that your objection may be to a specific piece of the comic's particular presentation: "random" is often used to mean "arbitrary" and people might think they can do it in their head? Of course I agree that anything people do with their heads is almost certainly insecure - brains are piss-poor sources of entropy. Would your objection be fixed entirely if it called out explicitly that the words need to be picked mechanically (computer, dice, something) with a uniform distribution? Anyway, the thing that I like about the comic is that it presents a specific means of choosing a password that is simultaneously secure and memorable, and the only misconception involved would be from misinterpretation of the comic (which, as noted above, does seem possible). Anything else someone comes up with on their own is likely to be less secure, less memorable, or both, so referring to the comic as promulgating a misconception bugs me. Regarding the last, I don't think we were ever arguing about passphrases in general, but about a particular way of generating them... passphrase really just means "long password", more or less, and that doesn't provide a lot of guidance as to how to come up with one, and leaving people to their own devices is how we wind up with ~60% of passwords being horribly crackable.
      - laumars 14y ago
bnegreve 14y ago
Yes, it's pretty secure against brute force. However if everyone start doing this, I suspect that we're going to have a lot of passwords like "I am hungry today" or even "car house hello red" which are both rather weak against an attack that would combine the most frequent words. You can't really prevent people from using common words and common patterns to build their password and hackers are going to use this fact. So my problem is that it gives the impression to be very secure whereas it's only secure under some conditions. (You have to pick words uniformly among the list of words.) Just like old password...
- dllthomas 14y ago
  You have to pick the words uniformly, yes. Thankfully, that's easy to do (rl -c 4 wordfile), and can be made easier. The point isn't "make up passwords that look like this" - it's "using this algorithm you get passwords that look like this that have this level of security[1]," and it's way easier than generating a secure and memorable password by other means. [1] As I've said in a few places, the actual dictionary size and number of words should be tweaked to make the security level appropriate for your needs, which will vary by application and grow over time.