6 ms·

How this affects popular premise that a passphrase is much better than a password?

venomsnake 13y ago
The popular myth you mean. Human brain is crap RNG and producer of entropy no matter what you do - it will still be crap.
- moe 13y ago
  Phrases with good entropy are easier to remember than 'words' with good entropy. DvAvRxiBAZaI1A3R Horse.. in a box riding a fish! Which one would you prefer to memorize and type in?
  - coldtea 13y ago
    Until you find out the service you use silently drops everything after the 8th character...
  - qnr 13y ago
    Some nitpicking: the passphrase is not as good as it seems. It consists of two parts ("horse in a box" and "riding a fish") both of which can be found in e.g. Google's n-gram corpus [1]. The Google's corpus has on the order of 2^32 n-grams so even assuming you chose these two at random, you get only 64 bits of entropy. There is also some punctuation (let's be generous and say it gives 10 bits), so the entire passphrase is about 74 bits of entropy. While very good, this is probably not enough to protect your bitcoin life savings or a truecrypt container that can implicate you in a serious crime (the reason being that Moore's law may well make 74-bit passwords easily crackable in 10 years or so) For comparison, the first password you provided (16 random alphanumeric characters) has 95 bits of entropy. [1] http://books.google.com/ngrams/graph?content=horse+in+a+box%2Criding+a+fish&year_start=1800&year_end=2000&corpus=15&smoothing=0&share= http://books.google.com/ngrams/graph?content=horse+in+a+box%...
- phaemon 13y ago
  What if I do: echo $( shuf -n 4 /usr/local/share/4000-common-words )
  - venomsnake 13y ago
    still won't help. This is security trough obscurity. It works only if the attacker don't suppose you use passphrase. 4000^4 gives 256000000000000 giving 3.3 bits of entropy per decimal digit it comes to 50 bits of entropy. Not too shabby but not that secure either. Your PCs rng may play you dirty tricks. And of course there are all kind of legacy systems with password limitations to 32 or 16 character, but above 8 etc etc which would further reduce the pool. Of course you could try your own password deriving mechanism. Take the first 16 characters of bcrypt(username,site domain) it will produce awesome passwords for any site that you will have easy time producing when needed. Until the hackers begin to suspect what you use if it becomes widespread. (Disclaimer - not a cryptographer or security expert or particularly competent in anything)
    - qnr 13y ago
      > Take the first 16 characters of bcrypt(username,site domain) Hey, that's the very definition of security through obscurity ;) Here's a thought experiment I use when estimating security of similar password schemes: imagine you asked someone to come up with 1000 different mechanisms of generating passwords based on username and domain. Is your scheme is likely to be among them? If yes, this means it provides less than 10 bits of security.
    - phaemon 13y ago
      It is not security through obscurity. It works even when the attacker knows I use a passphrase and has a copy of my dictionary. It's about the same security as a random 8 character password with lower and upper case, numbers and choice of 10 symbols. Maybe that's no longer secure enough; I don't know how fast password crackers are now. So use "shuf -n 5" instead.
      - StavrosK 13y ago
- zokier 13y ago
  Passphrases do not need to be (completely) human-generated. On a related note, has anyone analyzed the entropy of markov chain generated passphrases?
  - anelson 13y ago
    A while back I played with this a bit. http://apocryph.org/archives/556 http://apocryph.org/archives/556 and http://apocryph.org/archives/693 http://apocryph.org/archives/693 Summary: Highly entropic Markov-generated phrases are long and hard to remember.

The popular myth you mean. Human brain is crap RNG and producer of entropy no matter what you do - it will still be crap.

moe 13y ago
Phrases with good entropy are easier to remember than 'words' with good entropy. DvAvRxiBAZaI1A3R Horse.. in a box riding a fish! Which one would you prefer to memorize and type in?
- coldtea 13y ago
  Until you find out the service you use silently drops everything after the 8th character...
- qnr 13y ago
  Some nitpicking: the passphrase is not as good as it seems. It consists of two parts ("horse in a box" and "riding a fish") both of which can be found in e.g. Google's n-gram corpus [1]. The Google's corpus has on the order of 2^32 n-grams so even assuming you chose these two at random, you get only 64 bits of entropy. There is also some punctuation (let's be generous and say it gives 10 bits), so the entire passphrase is about 74 bits of entropy. While very good, this is probably not enough to protect your bitcoin life savings or a truecrypt container that can implicate you in a serious crime (the reason being that Moore's law may well make 74-bit passwords easily crackable in 10 years or so) For comparison, the first password you provided (16 random alphanumeric characters) has 95 bits of entropy. [1] http://books.google.com/ngrams/graph?content=horse+in+a+box%2Criding+a+fish&year_start=1800&year_end=2000&corpus=15&smoothing=0&share= http://books.google.com/ngrams/graph?content=horse+in+a+box%...
phaemon 13y ago
What if I do: echo $( shuf -n 4 /usr/local/share/4000-common-words )
- venomsnake 13y ago
  still won't help. This is security trough obscurity. It works only if the attacker don't suppose you use passphrase. 4000^4 gives 256000000000000 giving 3.3 bits of entropy per decimal digit it comes to 50 bits of entropy. Not too shabby but not that secure either. Your PCs rng may play you dirty tricks. And of course there are all kind of legacy systems with password limitations to 32 or 16 character, but above 8 etc etc which would further reduce the pool. Of course you could try your own password deriving mechanism. Take the first 16 characters of bcrypt(username,site domain) it will produce awesome passwords for any site that you will have easy time producing when needed. Until the hackers begin to suspect what you use if it becomes widespread. (Disclaimer - not a cryptographer or security expert or particularly competent in anything)
  - qnr 13y ago
    > Take the first 16 characters of bcrypt(username,site domain) Hey, that's the very definition of security through obscurity ;) Here's a thought experiment I use when estimating security of similar password schemes: imagine you asked someone to come up with 1000 different mechanisms of generating passwords based on username and domain. Is your scheme is likely to be among them? If yes, this means it provides less than 10 bits of security.
  - phaemon 13y ago
    It is not security through obscurity. It works even when the attacker knows I use a passphrase and has a copy of my dictionary. It's about the same security as a random 8 character password with lower and upper case, numbers and choice of 10 symbols. Maybe that's no longer secure enough; I don't know how fast password crackers are now. So use "shuf -n 5" instead.
    - StavrosK 13y ago
zokier 13y ago
Passphrases do not need to be (completely) human-generated. On a related note, has anyone analyzed the entropy of markov chain generated passphrases?
- anelson 13y ago
  A while back I played with this a bit. http://apocryph.org/archives/556 http://apocryph.org/archives/556 and http://apocryph.org/archives/693 http://apocryph.org/archives/693 Summary: Highly entropic Markov-generated phrases are long and hard to remember.