6 ms·
Sounds like a "correct battery horse staple" would fit the bill
by np_tedious 9y ago
Sounds like a "correct battery horse staple" would fit the bill
- chiph 9y agoOr use a memorable phrase from literature. > This was not the last encounter between Bobby Shaftoe and Goto Dengo
- mighty_atomic_c 9y agoNecronomicon quote? Nice. This has me thinking about what I can do to make my security answers to security questions untethered from PII. A book quote is a really good idea.
- chiph 9y agoClose! Cryptonomicon. I'm guessing that having every book loaded into a password cracking database, subdivided and indexed by each leading phrase word, is still computationally infeasible for non-government actors.
- luiscarloscb 9y agoNo need to have every book loaded, only the top 50000~ read by people who would use that method of passphrase generation should work fine (and be feasible for almost everyone). Cryptonomicon would probably be in that list.
- Natanael_L 9y agoBitcoin brain wallets based on obscure Africa poems have been successfully cracked. Don't trust your choice of obscure books to be sufficient.
- chiph 9y agoI need to look into that some. If I walk into a library, pick a floor, aisle, shelf, book, and page at random (just walk, don't think about it), and use a phrase that is a minimum of 12 words long -- is that more random than what I presume happened here, where someone knew that their target liked that style of poetry and was able to concentrate their search on that genre? ( a "crib" in Bletchley Park terms) The comments about English grammar are correct - classes of words (nouns, verbs, adverbs, etc) do fall in certain positional order and frequency analysis becomes important. A brute-force attacker would have to work through four types of passwords - the commonly used passwords like "12345" and "letmein", language-based phrases (like my not-great idea), language-based phrases with letter substitution (leet-speak, etc), and then truly random letter sequences.
- Natanael_L 9y agoWhat's happening is that people collect endless phrases and alter them with a ton of standard manipulation schemes, compute the corresponding private and public keys & addresses for all the variations, create a lookup table for the addresses and private keys, and as soon as they see a known keypair in use then they use the corresponding private key to swipe the funds.
- FabHK 9y agoSee my comment above - unless I'm mistaken, taking all 2 to 24 word quotes from the most popular 1 million novels gives you about 40 bits of entropy (less than a password of length 7), and can easily be stored on one hard drive. In other words, feasible even for some script kiddie in mom's basement.
- ajmurmann 9y agoI would definitely be weary of using the same answer in multiple places. Even more so than with passwords. These stupid answers clearly get stored unhashed (how else would they be verified via phone?). Do if the system gets compromised the attacker now has your security question response for multiple targets. Other than being pronounceable I see the exact same requirements for security questions as for passwords. If anything they need to be stronger.
- teddyh 9y agoNope. If a phrase from literature is “memorable”, it’s guessable. The logic of passwords is simple, once you realize that all humans are terrible random number generators. When you allow any part of your password to be chosen by a human, i.e. yourself, you have to assume that the human-chosen part is known to an attacker. The solution is to generate passwords with enough random bits to satisfy current demands. And by “generate” I of course mean to allow a real number generator (either a computer, or dice, or anything really random; i.e. something a casino would accept) to choose the password for you. Without any restrictions except a desire to minimize length, you get the classic unmemorable 0vT2GVlncZ4pZ0Ps-style passwords. If you add the restriction “must be a sequence of english words”, you get xkcd-style “correct horse battery staple” passwords. Both are fine, since they contain enough randomness not generated by a human. But if you yourself choose, either old-style “Tr0ub4dor&3” or passphrase “now is the time for all good men”-style, you have utterly lost, since nothing has been randomly chosen, and “What one man can invent, another can discover.”. Note: this also applies if you run a password generator and choose a generated one that you like. Since you have introduced choice, you have tainted the process, and your password now follows an unknown number of intuitive rules (for instance, there was a story here on HN some time ago about how people prefer the letters in their own name over other letters of the alphabet), and these rules can be exploited by an attacker.
- pault 9y agoI have no idea who is downvoting you; this is perfectly correct. In fact, one of the (minor) plot points in the quoted book is a cyphertext getting broken because the person generating one time pad keys looks at the letters!
- tonyztan 9y agoDiceware is memorable but not guessable. Source: https://en.wikipedia.org/wiki/Diceware https://en.wikipedia.org/wiki/Diceware https://www.rempe.us/diceware/#eff https://www.rempe.us/diceware/#eff
- teddyh 9y agoAgreed, but the context was using memorable phrases from literature, in which case they are guessable. Post edited to clarify.
- pault 9y agoI like the appeal (and the book) but I recall, when researching diceware, reading that this is a terrible idea in practice since the entropy is lowered dramatically by using natural language that's already in the public record. Even if they can't put every printed phrase into a lookup table, the probability of certain words following others wrecks the entropy.
- pxndx 9y agoIndeed, but for the attack discussed here (someone calls support and pretends they're you) you don't need that much entropy, as you can't test different phrases quickly.
- Natanael_L 9y agoYou just need a larger number of random words to reach the same entropy as random passwords. It's not like your random password is made up from secret alphabets!
- pault 9y agoSentences aren't random.
- xelxebar 9y agoYou seem to be misunderstanding how diceware works. You randomly generate numbers by throwing dice. Every five rolls indexes exactly one "diceware" word. So even if an attacker knew we were using diceware, each word contains log2(6^5) = log2(7776) ≈ 12.9 bits of entropy. If you want 128 bits of etropy in your security question field, then just randomly generate 10 diceware words. This is comparable to choosing 20 random printable ascii characters or so. Since we pick the words by literally throwing dice, English grammar has nothing to do with it.
- pault 9y agoI was responding to someone who was recommending using sentences from books as passwords. Hence the comment about grammar.
- FabHK 9y agoMedian novel has some 65k words. Take all (consecutive) quotes of 2 to 24 words, and you have some 1.5m phrases. Take the top 666k books (apparently there've been about 130m titles been published in total, about 5m in the Amazon Kindle store), and you're at about 1e12 phrases, or 40 bits of entropy, or worse than a password with 7 random letters/digits/symbols. You could probably improve on it considerably by selecting fewer books, and only taking quotes starting at some punctuation mark. For a naturally throttled attack like here (on the phone) that's fine, but for an offline attack (where the attacker has access to the password hash) that can be cracked within days.