4 ms·

Argh! The XKCD entropy comic. Back away slowly.. The "4 common words" password meme was around a lot after that comic. However, such passwords are definitely n

by ErrantX 11y ago

Argh! The XKCD entropy comic. Back away slowly.. The "4 common words" password meme was around a lot after that comic. However, such passwords are definitely not secure because a good dictionary attack will break it in hours. You do not have as much entropy as you think with them. The same problem tangentially applies to his suggested password schema to. The problem is: as soon as you start using human word or pseudo words then your complexity decreases significantly. With that said he has a point: password complexity schemas as employed by websites are not good enough. It should enforce length and complexity properly (not by saying "you must have these types of characters" but by really analysing the password). I appreciate the UX problems involved there... but then we could push people towards using password managers and auto-generated passwords. Summary: use a password manager and auto-generate complex passwords.

desdiv 11y ago
Can you explain why the XKCD scheme is weak to dictionary attacks? Using the 2048 common words example from the comic, there would be 2048^4 = 1.8e13 four word combinations. I don't see any possible attack that's faster than brute-force here.
- ErrantX 11y ago
  Of course, it's not the worst schema. But it gets a lot more credit than it is worth. Using dictionary words reduces the entropy of your password significantly. And for a cracker it can be trivial to attack passwords of that form. Given the sort of compute power you can obtain cheaply nowadays, attacking 4-word schemas (especially given people tend to use common words) is not hard. It's to some degree security through obscurity: no, a cracker will not know your schema in advance but he will attempt to attack multiple schema types. If you're the sole target then that's probably not a concern - it would be a major effort, with limited rewards, to attack your unknown password schema. But if yours forms part of a larger set of passwords being attacked (where the use of multiple schemas and attacks will reap high rewards) then you're at more risk. IMO, for all the password schemes that people come up with there is no good alternative to a long, randomly generated string with multiple character types. Always use a password manager!
  - aianus 11y ago
    > especially given people tend to use common words You don't pick the words yourself, you choose them at random. That's the whole point. > Given the sort of compute power you can obtain cheaply nowadays, attacking 4-word schemas (especially given people tend to use common words) is not hard. If the password is hashed with bcrypt with a work factor of 10 (the default in Rails), it would take ~5500 years to crack a single xkcd-style password on a single modern CPU core. Maybe 4 words aren't enough to protect you from the NSA, but they're enough to protect you from Joe Botnet and his db dump.
    - ErrantX 11y ago
      Except, how can you be sure your password was stored securely? You should never assume that. > You don't pick the words yourself, you choose them at random. That's the whole point. Suggest: you're supposed to choose them at random. In practice (source: 5 years as a security analyst) this does not happen. People are predictable!
      - aianus 11y ago
        > Except, how can you be sure your password was stored securely? You should never assume that. You don't have to. You can use a password manager with an open protocol (like 1Password) where you can tell the db is encrypted using a key correctly and slowly derived from your master xkcd-style password. If done correctly, it's a much better scheme than randomly generated characters because at the same level of entropy you wind up with a password you can actually remember and type quickly and use consistently in conjunction with a password manager.
  - reddytowns 11y ago
    How long does it take to crack a 4 word password, vs a 3?
  - usrusr 11y ago
    > It's to some degree security through obscurity: no, a > cracker will not know your schema in advance but he will > attempt to attack multiple schema types. If you put it like that, then passwords are security through obscurity too, since they are only secure because the attacker does not know the password? It's really all about having your own, personal schema. Even a slight variation of a popular one will put you safely out of the path of that multi-schema dragnet if the resulting password isn't part of any of the schema spaces. Just make sure it really is your very own variant and not something many others would also come up with. Add a part of that old line noise password you still remember from university at a fixed position of the word list or something like that. Even a recycled ATM PIN might help, your word list just got 9999 words longer. Add those digits to the individual words? 9999 new dictionary schemas to process. To play on the old Clarke: any sufficiently high number of possible password schema variations is indistinguishable form requiring a true brute force attack. > Always use a password manager! Yay, a single, juicy target, synchronized to any number of devices of various levels of tamper resistance, maybe even with some user-friendly automation that will happily hand out login pairs to anything that has temporarily taken control of your browser. With local exploits empowered by such a big sign saying "this is where the good stuff is kept", do you know a good writeup of practical password manager risk mitigation strategies? Like adding a brain-stored suffix to the more important ones and so on, so that an attack script would also need to do key logging or mild individual brute forcing. I'm sure there must be an established body of expert opinion on this somewhere.
DanBC 11y ago
What do you mean when you say "dictionary attack", because I think you're talking about something to me.
leni536 11y ago
The XKCD entropy comic assumes dictionary attack. This is why he only counts 11 bits of entropy (2048 variations) for each word.
gambiting 11y ago
No. For a dictionary attack, someone would need to know that you are using words. They would need to know if they are separated by spaces, or dots or slashes. The probability of someone knowing your personal scheme is fantastically low, unless they already know one of your other passwords and can guess it. A password like: "Żółć zżółkła w gąszczu fantazyji!" Is absolutely impossible to crack in any reasonable amount of time. It's a perfectly valid sentence in Polish, but the attacker would need to know to use a Polish dictionary, and also a one of these words is an old-Polish word which will not appear in any modern dictionaries. Finally, they would need to know you have an exclamation mark at the end. It's literally impossible for someone to guess all of that, and this password is infinitely easier to remember than !@#%#$@j4jnvdbst$#^@%$@#$#
- pwman 11y ago
  Some of your sites are storing your password in plain text, see http://plaintextoffenders.com/ http://plaintextoffenders.com/ for a few. Once a single one of those is hacked your method is exposed and it goes from improbable to practical.
- ErrantX 11y ago
  What you're actually doing there, though, is applying security through statistics. No, an attacker will not know your schema. But she will know all about the common schemas. And you're risking her using your schema in her attacks. Your proposed password is much better than the one XKCD's proposes because you're using uncommon words and punctuation. And I agree, it's more secure.
- Natanael_L 11y ago
  It has literally been done already. Obscure African poems have been guessed.
  - gambiting 11y ago
    By people who knew to look for obscure african poems? I mean sure, you could guess a Polish sentence if you used a Polish dictionary, but how likely is that?

by ErrantX 11y ago

desdiv 11y ago

Can you explain why the XKCD scheme is weak to dictionary attacks? Using the 2048 common words example from the comic, there would be 2048^4 = 1.8e13 four word combinations. I don't see any possible attack that's faster than brute-force here.

ErrantX 11y ago
Of course, it's not the worst schema. But it gets a lot more credit than it is worth. Using dictionary words reduces the entropy of your password significantly. And for a cracker it can be trivial to attack passwords of that form. Given the sort of compute power you can obtain cheaply nowadays, attacking 4-word schemas (especially given people tend to use common words) is not hard. It's to some degree security through obscurity: no, a cracker will not know your schema in advance but he will attempt to attack multiple schema types. If you're the sole target then that's probably not a concern - it would be a major effort, with limited rewards, to attack your unknown password schema. But if yours forms part of a larger set of passwords being attacked (where the use of multiple schemas and attacks will reap high rewards) then you're at more risk. IMO, for all the password schemes that people come up with there is no good alternative to a long, randomly generated string with multiple character types. Always use a password manager!
- aianus 11y ago
  > especially given people tend to use common words You don't pick the words yourself, you choose them at random. That's the whole point. > Given the sort of compute power you can obtain cheaply nowadays, attacking 4-word schemas (especially given people tend to use common words) is not hard. If the password is hashed with bcrypt with a work factor of 10 (the default in Rails), it would take ~5500 years to crack a single xkcd-style password on a single modern CPU core. Maybe 4 words aren't enough to protect you from the NSA, but they're enough to protect you from Joe Botnet and his db dump.
  - ErrantX 11y ago
    Except, how can you be sure your password was stored securely? You should never assume that. > You don't pick the words yourself, you choose them at random. That's the whole point. Suggest: you're supposed to choose them at random. In practice (source: 5 years as a security analyst) this does not happen. People are predictable!
    - aianus 11y ago
      > Except, how can you be sure your password was stored securely? You should never assume that. You don't have to. You can use a password manager with an open protocol (like 1Password) where you can tell the db is encrypted using a key correctly and slowly derived from your master xkcd-style password. If done correctly, it's a much better scheme than randomly generated characters because at the same level of entropy you wind up with a password you can actually remember and type quickly and use consistently in conjunction with a password manager.
- reddytowns 11y ago
  How long does it take to crack a 4 word password, vs a 3?
- usrusr 11y ago
  > It's to some degree security through obscurity: no, a > cracker will not know your schema in advance but he will > attempt to attack multiple schema types. If you put it like that, then passwords are security through obscurity too, since they are only secure because the attacker does not know the password? It's really all about having your own, personal schema. Even a slight variation of a popular one will put you safely out of the path of that multi-schema dragnet if the resulting password isn't part of any of the schema spaces. Just make sure it really is your very own variant and not something many others would also come up with. Add a part of that old line noise password you still remember from university at a fixed position of the word list or something like that. Even a recycled ATM PIN might help, your word list just got 9999 words longer. Add those digits to the individual words? 9999 new dictionary schemas to process. To play on the old Clarke: any sufficiently high number of possible password schema variations is indistinguishable form requiring a true brute force attack. > Always use a password manager! Yay, a single, juicy target, synchronized to any number of devices of various levels of tamper resistance, maybe even with some user-friendly automation that will happily hand out login pairs to anything that has temporarily taken control of your browser. With local exploits empowered by such a big sign saying "this is where the good stuff is kept", do you know a good writeup of practical password manager risk mitigation strategies? Like adding a brain-stored suffix to the more important ones and so on, so that an attack script would also need to do key logging or mild individual brute forcing. I'm sure there must be an established body of expert opinion on this somewhere.

DanBC 11y ago

What do you mean when you say "dictionary attack", because I think you're talking about something to me.

leni536 11y ago

The XKCD entropy comic assumes dictionary attack. This is why he only counts 11 bits of entropy (2048 variations) for each word.

gambiting 11y ago

No. For a dictionary attack, someone would need to know that you are using words. They would need to know if they are separated by spaces, or dots or slashes. The probability of someone knowing your personal scheme is fantastically low, unless they already know one of your other passwords and can guess it. A password like: "Żółć zżółkła w gąszczu fantazyji!" Is absolutely impossible to crack in any reasonable amount of time. It's a perfectly valid sentence in Polish, but the attacker would need to know to use a Polish dictionary, and also a one of these words is an old-Polish word which will not appear in any modern dictionaries. Finally, they would need to know you have an exclamation mark at the end. It's literally impossible for someone to guess all of that, and this password is infinitely easier to remember than !@#%#$@j4jnvdbst$#^@%$@#$#

pwman 11y ago
Some of your sites are storing your password in plain text, see http://plaintextoffenders.com/ http://plaintextoffenders.com/ for a few. Once a single one of those is hacked your method is exposed and it goes from improbable to practical.
ErrantX 11y ago
What you're actually doing there, though, is applying security through statistics. No, an attacker will not know your schema. But she will know all about the common schemas. And you're risking her using your schema in her attacks. Your proposed password is much better than the one XKCD's proposes because you're using uncommon words and punctuation. And I agree, it's more secure.
Natanael_L 11y ago
It has literally been done already. Obscure African poems have been guessed.
- gambiting 11y ago
  By people who knew to look for obscure african poems? I mean sure, you could guess a Polish sentence if you used a Polish dictionary, but how likely is that?