5 ms·

XKCD's diceware argument fails under certain conditions. Computationally very hard to crack, but when plucked from actual phrases that have been uttered; weak.

• DanBC 11y ago
  I'm not sure I understand how an infinite monkey attack would work against diceware. Let's assume a word list of 7776 words. All words are lower case alpha. The attacker has pur wordlist. And the attacker knows there are seven words in the passphrase. That's still 7776^7. Even if we prune the wordlist ("I'm not using 'zerg' in my phrase", "I rolled 11111, that's not random so I'll roll again") it's still not an attackable space.
  • nsmalch 11y ago
    As a rule of thumb, I would go after natural language phrases first, because it is impossible to tell if the phrase was machine-generated. It's nearly impossible to arrange dots randomly on a page with a pencil because there is always some structure or engrained rigidity in human guesswork. There is also the possibility that the dots were done by 'inception', and certain biases were programmed in via subliminal messaging. Don't trust humans to do a machine's tasks.
    • DanBC 11y ago
      Humans use dice to generate randomness. They throw 5 dice, to get a five digit number. They look up that number on a list to get a word. They repeat this process until they have a 7 word phrase. So, there are weaknesses if humans roll the 5 dice and get 1, 1, 1, 1, 1 and then say "That's not random, I'll roll again"[1] or they roll a number, look it up and say "I'll never remember 'zerg', I'll roll again".
      • JoeAltmaier 11y ago
        Rolling again, is no weakness at all. The next roll is also random and exactly as unguessable as the first. If the game was done 'without replacement' then the field would be reduced, but it isn't, and the field is unimaginably huge anyway. There is no effect whatsoever by 'rolling again' until you are happy with the result. My buddy Tom always generates UUIDs by hitting the button several times. It gives him pleasure to 'waste' all those random numbers.
        • DanBC 11y ago
          With diceware there's a list of 7776 words. When someone rolls 1,1,1,1,1 and rejects that word they've cut down the word list to 7775 words. That's tiny, but it is a change.
          • deleted 11y ago
            [deleted]
          • JoeAltmaier 11y ago
            Right, for word choice it is significant. I was thinking, rejecting the whole password pattern.
            • just_curioussss 11y ago
              By rejecting a certain pattern you weakening the whole password scheme. It is no longer random, it is human chosen. An attacker can under certain circumstances exploit this behavior. For example, if they notice you are picking shorter words or words that consist of certain characters, they will have an easier time to crack the password. Whole categories or patterns can be rejected because of that, reducing the search space. An extreme version of your method, is picking only the patterns that relate exclusively to you, like picking your favorite music or hobbies. Then the whole scheme becomes useless.
              • JoeAltmaier 11y ago
    • pmoriarty 11y ago
      Randomness is not a property of the procedure used to generate a given set of numbers, but is rather a potential property of a set of numbers itself.
• aruggirello 11y ago
  Diceware proper is not 'plucked from actual phrases that have been uttered'. It's a random sequence obtained by throwing a dice a number of times (hence the name). This means you can't lookup your e-book collection for an exact phrase to use (eg. a famous quote). Moreover, diceware can be set up with any dictionary, and nobody stops you from computing your own dictionary. If you do that, good luck to the bruter attempting to break your passphrase! BTW there is no limit on the number of terms in your diceware passphrase, so if/when brute force makes 5-term phrases too weak, users may just add one or two more terms.
  • nsmalch 11y ago
    Yeah what I meant is that sometimes the phrase appears like natural language, and was probably uttered once, if not on a stray ebook than somebody once said it. Of course then we have have the question of whether history starts the moment it is electronically recorded. If NLG upsets you, you can always settle for a Markov chain and some atmospheric noise to seed the random values