Xkcd Password Generator

http://preshing.com/20110811/xkcd-password-generator

by preshing • 15 years ago

347 291 15 years ago

ck2• 15 years ago

I've been doing this for years on sites that allow long passwords - "pass sentences" - but I also throw in a number or two.

buro92• 15 years ago

I've also been doing this for years, but with bits of my post code thrown in to fulfil those edqe cases where complexity requirements are needed.

petenixey• 15 years ago

... random combinations of bike bits plus a greater London post code. Give me enough monkeys and typewriters and I could take you ;)

jwingy• 15 years ago

+1 (TM now I guess)

You could have four word phrases that are maybe only ~12 characters, which if there are only alphabetical characters in the password, are still very much crackable via GPU brute force (http://mytechencounters.wordpress.com/2011/04/03/gpu-passwor...)

mrspeaker• 15 years ago

He he, reminds me of the password generator I made concatenating 3 words from the list of the "500 most common passwords": http://www.mrspeaker.net/2009/01/09/make-secure-passwords/

The top 500 list has an awful lot of naughty words - so the phrases are pretty easy to remember ;)

adnam2• 15 years ago

Such a password scheme provides much less than 44 "bits" of entropy. Considering the use of 4 randomly chosen words from the c.170000 english words in general use, means we can guess the paraphrase in around 2^22 tries - even less than "Tr0ub4d0r3&".

EDIT: I'm totally wrong, it's more like 2*10^22 ... oops!

TetOn• 15 years ago

Wouldn't you first have to know that the passphrase consists of four randomly chosen words (eg not three, five, or eight)? To me, that's the underlying strength of the approach that the comic (!) is trying to highlight.

burgerbrain8• 15 years ago

The entropy is actually calculated with the assumption that the attacker already knows those things. If they don't, then it is higher.

meentsbk• 15 years ago

There is a really interesting discussion on using passphrases from stackexchange that is probably worth linking: http://security.stackexchange.com/questions/6095/xkcd-936-sh...

burgerbrain8• 15 years ago

There is no need for scare quotes around bits. The term is being used in a technically correct fashion. https://secure.wikimedia.org/wikipedia/en/wiki/Bit#Informati...

adnam2• 15 years ago

Err, yes thanks. I was trying to emphasise the fact that the multiplier of entropy is not the "bit", but the "word" (in the linguistic, rather than the computer architecture sense)

drblast• 15 years ago

Randall's math is spot on in this comic.

Assuming the attacker knows the the password creation method (and the math assumes the attacker does in the first case), then the attacker knows the word list and the passphrase algorithm.

11 bits per word gives you a grab bag of 2048 possible common words. To guess the password, assuming each word is unique, the attacker needs to try

2048 * 2047 * 2046 * 2045 = 17,540,692,561,920

possible combinations. Initially, you'd think an eleven character password with totally random uppercase, lowercase, numbers and symbols would give you 66 ^ 11 combinations for 66 bits of entropy, but since nobody can actually remember such a random combination, the resulting passwords using these rules are much less secure than that.

ErrantX4• 15 years ago

Not a good idea, sadly. In fact I'd go so far to say this is a really bad suggestion; because it gives a false sense of security.

There is potentially a lot less entropy in this password than "Tr0ub4d0r&3", assuming the hacker is smart enough to realise he can trivially test combinations of dictionary words in very short amount of time.

(EDIT: I'm way out of touch with this; it's not as trivial as perhaps I figured. See lower in the thread)

However; it is in the right direction - introducing some sort of extra entropy can invalidate that form of attack and make this as secure as XKCD suggests.

What do I currently do? I take a reasonable length common word, do a string/number replacement as so:

H4ck3r N3ws

And then repeat it 3 or 4 times:

H4ck3r N3ws H4ck3r N3ws H4ck3r N3ws H4ck3r N3ws

For extra entropy mix it up:

H4ck3r N3ws H4ck3r News H4cker News Hacker News

That's a simple example - so long as you have a reasonably random scheme then it is not easy to test against, but is fairly simple to remember.

Bingo :)

(EDIT: for the down voter(s) note: XKCD specifically says random common words - obscure words are another matter)

darklajid5• 15 years ago

> he can trivially test combinations of dictionary words in very short amount of time.

Explain the reasoning behind this, please.

Start with: You don't know the dictionary I used, but have to use one that seems 'good enough' (i.e. a superset of mine, if possible).

How many words are in there?

How many combinations can you create for 'two word phrases'? (You don't know the length of my phrase)

How many for three?

How many for four words?

hesselink• 15 years ago

The XKCD criticism of the 'bad' password has the same problems. How does the hacker know I have this kind of password (starting with a real english word, for example)?

burgerbrain8• 15 years ago

In fact, even if the attacker:

1) Knows this scheme was used.

2) Knows the list of words you used.

3) Knows how many words you used.

You will still have that amount of entropy. Diceware entropy values are calculated with all three of these assumptions already made.

ErrantX4• 15 years ago

> Start with: You don't know the dictionary I used, but have to use one that seems 'good enough' (i.e. a superset of mine, if possible).

People are likely to use a standard English dictionary. In my experience (which is exactly within this field) people use a fairly tight subset of the English vocabulary.

So I would be quite happy to test for a dictionary of, say, 100,000 words and be hopeful of a good hit rate (note that XKCD says common words, which is easily missed)

Our software has a test (which runs about third in its list of tests) which does dictionary combinations up to three words (two words is quite a commonly used password based on our statistics) with a dictionary size of <s>175,000</s>17,500. (Edit: sorry, apparently it is an order of magnitude smaller, I checked with one of the engineers :)) This includes English words plus a few commonly used foreign/slang terms. The hit rate on this is fairly high.

(we crack document/windows passwords mainly)

You could of course choose deliberately obscure words to invalidate this - but they aren't so easy to remember (so people will tend not to).

If someone is going out of their way to secure a password, sure, you're going to hit a brick wall. But what every password scheme tends to forget is the "human factor" whereby people not concentrating on being secure will introduce attack vectors.

bunchesofdonald• 15 years ago

The comic is already taking worst case scenario into account, that the cracker knows that your password is made of words and which dictionary you used to generate the password.

In the comic he is using a 2048 word dictionary, which gives 11 bits of entropy per word (log2(2048)), with a password made up of four words that gives a total of 44 bits of entropy.

But if we were to assume that the cracker knows nothing about our password, say other than it being all lowercase a-z, then we have an entropy per character of log2(26) or 4.7. For the phrase "correct horse battery staple", which has a length of 28, the bit entropy of that phrase, under those conditions is 4.7 * 28 = 131.6. Which is nearly to the point of the cracker being more likely to find a collision.

pavel_lishin2• 15 years ago

> H4ck3r N3ws H4ck3r News H4cker News Hacker News

Maybe you have an excellent memory, but I'd forget this in a week. "Now let's see, is it the third 'hacker' that has the 4 AND the 3 in it? Or the 2nd?"

djackson• 15 years ago

He's just removing the right-most letter/number swap in each iteration.

dpark8• 15 years ago

> H4ck3r N3ws H4ck3r News H4cker News Hacker News

This is a terrible idea. It's one thing to ask a person to remember which characters they replaced in a word. It's another thing entirely to ask them to remember three different ways they swapped characters. This is a recipe for having to brute-force your own password. It's also still not as secure as you might imagine. There's very little entropy added by swapping characters (even though I do it as well), because there are very few substitutions that people make. "Hacker News Hacker News Hacker News" is nearly as secure as your convoluted 3rd passphrase, but a lot easier to remember.

The repeat-three-times thing is probably not great advice, either. If this became popular, it would be trivial to add this to brute-forcing code, and it doesn't add as much entropy as adding just one extra character.

I don't think the XKCD suggestion is actually good, either. Open a book and pick a medium-length sentence. There's your passphrase: an n-gram chosen arbitrarily from the corpus of (probably) English literature containing mixed-case and punctuation. You've got a ton of entropy there.

klipt• 15 years ago

> You've got a ton of entropy there.

Nope - http://news.ycombinator.com/item?id=2873474

lukeschlather• 15 years ago

>H4ck3r N3ws H4ck3r News H4cker News Hacker News

You can add equivalent entropy just by adding a few random special characters, a number, and a letter.

Personally, I prefer to type my passwords until I remember them. Therefore, my metric is "easy to type and hard to guess." If it's easy to type, I remember it via muscle memory, which is unbelievably better than trying to remember abstract symbols.

pilif• 15 years ago

Assuming that this method for generating passwords gets popular enough, brute force tools will begin to create an optimized attack for these passwords.

As there are so little words available, if I were to write a brute-forcing tool, I would try combinations of four words in my wordlist once I failed with my one-word-dictionary attack before I start trying out all characters.

But all is not lost: Either use more words or vary the amount of spaces you put between words. This way the dumb optimization "try four words delimited by space" wouldn't work on your password and they would have to go over to plain old brute forcing at which point, I agree, the longer, the better.

burgerbrain8• 15 years ago

https://secure.wikimedia.org/wikipedia/en/wiki/Diceware

Properly executed, this will protect you against brute force attacks. No need to do nonsense like adding more spaces.

Of course XKCD botched it and said an inadequate minimum length...

Notable quote from the article: "This level of unpredictability assumes that a potential attacker knows both that Diceware has been used to generate the passphrase, the particular word list used, and exactly how many words make up the passphrase."

darklajid5• 15 years ago

Was just about to quote that to you. Don't you think that you should take this quote into account when you say xkcd botched it?

ordinary• 15 years ago

Even 4 words is good enough for many use cases.

Tharkun• 15 years ago

Here's how I use diceware: 1) throw single die to determine number of languages 2) throw dice to determine which languages (number of iterations depends on the result of #1) 3) throw dice to determine language 4) throw all dice to determine first word in language 5) repeat #3, #4 until you've reached the desired number of words

salvadors5• 15 years ago

But the combinatorial explosion starts putting that out of reach fairly quickly.

Let's say you're restricting yourself to a dictionary of only 2000 common words.

A single word, up against a 1000-tries-per-second attack, would therefore fall within 2 seconds. Clearly bad. Adding a second word gives 2000^2 combinations to test against, which would require about an hour. Still not good. A third word, pushing that up to 2000^3, takes us to about three months, which is probably acceptable in many cases. The fourth word, at 2000^4 combinations, gets us to 500 years, which is well beyond what most people are ever going to need for a web-based password.

Now, if you want to bring this into the realm of passwords in other contexts, which can perhaps be brute-forced with several-billion-tries-per-second attacks, this approach still works: you just need to add an extra word or two. At 2,000,000,000 per second the four word combination might only take a couple of hours, but a fifth word takes that up to half a year, and a sixth out to the thousand years mark, whilst still falling easily within the standard 7±1 memory limit and being much much much easier to remember than m(yV7&NlxAIZNx3>&@p&8/kX.

iaskwhy2• 15 years ago

I always thought using two password fields with simple words would be much harder to break than one field only (which can be used to really strange passwords but also for simples ones as we all know). Someone care to calculate how much it would take to break it?

corin_• 15 years ago

Well it depends how it's stored, but assuming a fairly standard setup it wouldn't particularly help.

The main issue with website security isn't people brute forcing the website login box, it's people cracking the hashes after stealing them. So if you had two easy to crack hashes stored in the database, you crack them both and off you go.

iaskwhy2• 15 years ago

Oh, I was (like the article) assuming you would concatenate both words (add a space or something else in between if you want) and it would be all stored in just one field. What about it?

jsulak• 15 years ago

I prefer using a program like Password Safe (http://passwordsafe.sourceforge.net/), and use a safe password that's a long sentence (with punctuation). Then I can use arbitrarily long and complex passwords for all my accounts, and not have to worry about memorizing them individually. The password safe can even be synced across computers using Dropbox.

nollidge• 15 years ago

I prefer KeePass simply because it's got implementations on multiple OSs, as does Dropbox (to sync the password database file). So I've got it on my iMac, Android phone, Windows laptop, and Windows work PC.

mtogo2• 15 years ago

If you have an iPhone or don't want to use keepassx, you can use an online password manager like Passpack or Lastpass.

The downside is that you need to really trust the password manager, as they have all of your usernames and password.

shinratdr2• 15 years ago

1Password supports all those devices as well.

zobzu5• 15 years ago

I prefer using a digital key that's always going to beat the entropy of the memorable passwords

dredmorbius2• 15 years ago

GPG-encrypted free-form file (though it's fairly structured), edited via vim and a well-known "auto-encrypt/decrypt GPG files" configuration: http://vim.wikia.com/wiki/Encryption

(Actually, from that page, vim now has built-in blowfish encryption, which I'll have to look at -- yet another argument in favor of sharing tips on the 'TarTubes: you may learn something even when you're sharing your own knowledge).

dredmorbius2• 15 years ago

Erm: the blowfish encryption was in reference to the old '-x' vi encryption option (using a now pretty insecure Unix 'crypt' function).

A better "configure GPG edit mode" .vimrc is here: http://vim.wikia.com/wiki/Edit_gpg_encrypted_files

I believe that's based on the one first posted by Wouter Hanegraaff <wouter@blub.net>.

ZoFreX4• 15 years ago

I would actually advise going against this advice. While it isn't a best practice, password sharing can and does happen, as does shoulder-surfing. It would take a LOT of effort to memorise my password, but a simple four word password will probably be remembered by accident. In a year's time if I piss a friend off, I don't want my Facebook password to be readily accessible in their memory.

I think more people need to learn to remember arbitrary strings. There really is no way around that problem if you want a decently secure password, and it's rare someone has a "good memory" - in most cases they've just learnt how to remember things well.

(Note: This doesn't really apply to me or most of us here in most cases, but for example my WiFi password is of the form "Mycatsname9" and yet my neighbour still has to ask me for it whenever her phone forgets it)

darklajid5• 15 years ago

How do you share your preferred password? Because I guess everything but sending it per text/mail would be tedious, while it would work better with a couple of words.

Shoulder surfing: It's certainly a risk, but I'd say that prolonged shoulder surfing shouldn't be possible. If I type fast, it will be very hard to make out the phrase. If I type slow, you cannot stand around that long.

And - I'm not a security expert, but how much do you gain if you saw a couple of chars here? My intuition (yeah, shouldn't trust that) says that it's worse if I watch you and know the _first_ character of your password than you seeing the first 1-3 characters of the first word of my passphrase?

(We don't know the name of your cat, so judging the quality of the password or your neighbo(u)r's ability to remember it is hard)

ZoFreX4• 15 years ago

> And - I'm not a security expert, but how much do you gain if you saw a couple of chars here? My intuition (yeah, shouldn't trust that) says that it's worse if I watch you and know the _first_ character of your password than you seeing the first 1-3 characters of the first word of my passphrase?

Novel thought and possibly worth persuing, I hadn't thought of that. I want to re-iterate this isn't something I broadly apply across all my passwords or even many of them, just that for some users password sharing is a use-case.

commandar• 15 years ago

>I think more people need to learn to remember arbitrary strings.

The entire point is that humans aren't very good at doing this.

>(Note: This doesn't really apply to me or most of us here in most cases, but for example my WiFi password is of the form "Mycatsname9" and yet my neighbour still has to ask me for it whenever her phone forgets it)

This is actually exactly the kind of scenario where using pass phrases makes the most sense. WPA2 is vulnerable to rainbow table attacks; relatively long passphrases are both easier to remember for mere mortals and less likely to be broken by a rainbow table attack.

ZoFreX4• 15 years ago

> The entire point is that humans aren't very good at doing this.

How true is this? Because everyone that tells me "I have a bad memory" doesn't even know the most basic tricks.

> This is actually exactly the kind of scenario where using pass phrases makes the most sense

I agree, actually - I don't mind if my neighbour does remember it, I was just trying to illustrate that things that are easy to remember are remembered by accident, and things like that are easily forgotten without effort.

nxn• 15 years ago

So you're advising against what appears to be a more practical and secure methodology on the basis that it's worse when you share your password? If you share your password, your exact problem is that you're sharing your password -- it's not how easy or hard the password is to remember. In fact, why does this even have any significance when the person you're sharing it with can just write it down?

Oh and if within a year's time you do not change your password, that could very well be another problem. I think you'd be better off just using easy to remember pass phrases and changing them every once in a while. Shouldn't be a problem because they are, after all, easy to remember.

ZoFreX4• 15 years ago

> So you're advising against what appears to be a more practical and secure methodology on the basis that it's worse when you share your password?

Iff you share your password then yes, you should use a scheme more suitable for that. And yes we shouldn't be sharing passwords, and if we do we should be changing them, but in the real world where most people don't do that I don't think we should encourage passwords which their friends will remember easily - because that is a very common attack vector.

kragen20• 15 years ago

Yes, if you share your password, it's probably better to use a password that needs to be written down and can't be memorized, in order to have a chance of revocation. (Or you could just change your password.) But for most of us, most of the time, memorizable passwords are a boon.

nakkiel3• 15 years ago

This might come in handy:

shuf -n4 /usr/share/dict/words | tr '\n' ' '

eru6• 15 years ago

If you allow multiple occurrences of the same word, you can get slightly higher entropy while making the passwords potentially even easier to remember.

    echo $(for i in 1 2 3 4; do shuf -n1 /usr/share/dict/words; done)

(Sorry, I'm not very good at bash, so this loop is probably not idiomatic.)

bnegreve4• 15 years ago

for i in `seq 1 4`; :)

DufusM• 15 years ago

I don't think those words are very practical. For example, 4 consecutive runs produced:

shippon preannouncer half-hourly withgang egotize baffs chapter monolater photoengraver beachhead linguidental autoheader hazeled defloration exhumate barretries

none of which seem particularly easy to remember (or spell even).

nakkiel3• 15 years ago

It's like with any other program supposed to help you picking up a password; you run it a couple of times until you find something that ticks.

  Beirut ejecting sidings mourns

ddlatham4• 15 years ago

A lot of comments here seem to be missing the point.

The main point is to use passwords that give you the most "bang for the buck" in the sense of adding the most bits of entropy for the least difficulty of remembering. Adding an extra number, or punctuation, or certain numbers of repetitions generally adds only a little bit of entropy for a significant cost in additional challenge to your memory.

Our minds are well suited to remembering combinations of common words, and by stringing a few such words together, you can generate a larger search space than using a single word with a few substitutions. Even if the attacker knows the scheme you're using, he still must search through the space of combinations of common words, which XKCD is pointing out is quite large.

zobzu5• 15 years ago

171K words in the english language 4 words no spaces 171k^4 vs 255^8 for a 8 char pass

drcode3• 15 years ago

Incorrect: It's 171k^4 and 255^8.

(which works out to 8.55E20 and 1.78E19)

bnegreve4• 15 years ago

No, the single word password is based on a dictionary word with some chars replaced by other visually similar chars. That's much less than 8^255.

hvs• 15 years ago

It's actually closer to 92^8 (printable ASCII) or even 62^8 (if they only allow letters and numbers).

ddlatham4• 15 years ago

First, that's still beside the point. You shouldn't evaluate a password scheme solely by entropy if it is a password you intend to memorize. XKCD argues that it's easier to remember 4 random words than 8 random characters.

Second, your example isn't very good because it assumes that every 8 byte character (save one) is acceptable, which is rarely the case, especially if you are trying to memorize them.

Finally, as another commenter pointed out, you've got your math wrong, and even your example has more entropy for the words than the characters.

eLod• 15 years ago

i think you are missing the point: passwords should be hard to guess first and should be easy to remember second. the former is the stronger need.

let's say there are 500.000 english words you are choosing from and you use 4 words. that gives you 500000^4 possibilities. let's assume the words averages about 5 characters, so we will compare this to a 20(=4 words * 5 characters) character long password made of 26 types of character (english alphabet, not using numbers and other special characters), that gives you 26^20 possibilities. and 26^20 - 500000^4 ~= 2x10^28, or put it this way: (26^20) / (500 000^4) = 318 850.382..

i know a random sequence of 20 characters are very hard to remember, but 500.000 is an overestimation too. let's say we use special symbols too (50 characters) and the word dictionary has 100.000 words. (50^12) / (100 000^4) = 2.44 so we can say it is better to have a 12 character long password (made of alphanums + symbols) than 4 random word concatenated (i think 12 is somewhat a 'standard' for 'sensitive' passwords). and i would argue that on the long term multiple concatenated passwords are very hard to remember. i'm not saying this is a terrible approach, just not the silver bullet to the 'password problem' (which xkcd never claimed of course, and for 'non sensitive', 'reused'/'throwaway' passwords it may be a viable option).

edit: and i forgot about case sensitivity too.

dpark8• 15 years ago

Are you serious? You think it's easier to remember 12 random characters than to remember four English words?

g6M;`Zt3^,d" vs selected aardvark badminton winnings

The way the human brain works, it would be at least as easy to remember 12 random words as 12 random characters.

eykanal• 15 years ago

Don't forget spaces. And Poland.

Another point is that letter placement within words is significantly non-random. By intelligently choosing which letters to try in each position, the hacker could at the very least minimize the number of tries by an order of magnitude for the first word.

ddlatham4• 15 years ago

I'll grant you that it's more important to have a password be difficult to guess, but that doesn't obviate the importance of it also being easy to remember. Even better, let's look for password schemes that are harder to guess and easier to remember at the same time.

It's easy to compare the entropy of two schemes as you're doing in your comment, but it's more difficult to objectively claim which is easier to remember. You argue that a random sequence of 12 characters is easier to remember than 4 words. If so, then I'd agree it would be a better scheme. However, I don't think that's the case. To really settle the argument, we should do some experiments - maybe someone already has?

Here's some examples I used a generator to create:

gangster insert madden quartic

overlong cage figurine hardship

trimmer wholly movie nadir

Bt].iu@0Soc*

Vf+pIW;C>\vp

'.}]Ba,g%@vI

Which do you think are easier to remember?

barrkel• 15 years ago

The trouble is that by human intuitions, you think there's a strong inverse correlation between being hard to guess and easy to remember; but that's not always the case.

It's hard for humans to remember meaningless conjunctions of symbols, so we think they are hard to guess; so we err on the side of making them too short. Contrariwise, we think a sequence of just four words couldn't possibly be hard to guess because it's so easy to remember, but it's only easy to remember because we can use the meanings of the words to form an idea or image, something our brains are built for (unlike strings of meaningless characters).

This is why the word technique is better: it corresponds better with how we remember, while reducing two other risks: the risk of losing your password - non-trivial - and choosing too short a password.

gabaix2• 15 years ago

I make less typing mistakes with shorter, complicated passwords.

Long passwords are typing-error prone. With mobile devices, it gets worse, as typing is really painful.

ddlatham4• 15 years ago

I've had the opposite experience, where I'm more likely to mistype passwords with mixed case letters and symbols holding the shift key down too long. With mobile devices, it gets worse, as common words are easy to type, but symbols and mixed case are a pain.

It is a good point, though, that for frequently typed passwords on a good keyboard, you can engage your muscle memory. That allows you to type short passwords very quickly, and even remember passwords with your fingers that you've lost from your conscious memory!

mortenjorck• 15 years ago

I've started using song lyrics when given the option of an extra-long password. I can get a very long string with little effort, and it's trivial to remember.

The best part is that any automated attack would have to deal with ringtone popups.

gjm114• 15 years ago

Be aware that adding to the length simply by taking more of the lyrics adds very little entropy. If you're trying "Oh say can you see" then it doesn't take a lot of extra bits also to try "Oh say can you see by the dawn's early light what so proudly we hailed at the twilight's last gleaming".

Similarly, extended passages of text -- even if they don't come from a restricted corpus like that of song lyrics -- have less entropy than you'd think. A smaller number of independent random words is likely to be a better tradeoff.

lukev• 15 years ago

I don't think entropy is the whole story. I would argue that although security-through-obscurity is a terrible, awful practice for systems, it's not that bad for personal password schemes. Using a nonce "system" for passwords, even if it's mathematically low-entropy, is still secure, at least enough for personal use.

For example, if I use single dictionary words fed through a trivial ceasar cipher, then that is mathematically very low entropy. Realistically speaking, however, it's relatively safe if the cracker doesn't know that's what I'm doing, because it's impractical for crackers to compute all possible low entropy "alternative dictionaries."

khafra• 15 years ago

You'd be surprised. JTR does l33tspeak substitutions, one-row-up substitutions, keyboard walks, pretty much all of the common things everyone does because "no hacker would ever think of that."

y0ghur7_xxx• 15 years ago

Reminds me of this previous discussion: http://news.ycombinator.com/item?id=2450972

Maybe Randall was inspired by that post.

kahawe• 15 years ago

Original xkcd link: http://xkcd.com/936/

Oh and there are unfortunately way too many systems limiting your password to only 6 or 8 characters still in use today.

hm2k2• 15 years ago

What about sites that don't allow spaces?

I know hotukdeals.com only allows [a-zA-Z0-9] which sucks.

wisty3• 15 years ago

And also, sites that have a limit on password length. And sites that have a silent limit on password length, and secretly truncate it. And sites that have different truncation, depending on which form you use. And sites that require a Capitals, lowercase, and numbers, because nobody would just use name+birthday.

pavel_lishin2• 15 years ago

Leave the spaces out..?

duck2• 15 years ago

Exactly, or if the site requires numbers/symbols those three spots are perfect place to put those instead of spaces.

hm2k2• 15 years ago

That's not what is proposed here though.

The point is that one size does not fit all at the moment.

I guess developers need to change the way they handle passwords.

wisty3• 15 years ago

How about (NOT SECURE YET, IT NEEDS MORE ENTROPY):

    from nltk.corpus import wordnet as wn
    
    all_animals = set()
    def add_to_set(animal):
        all_animals.add(animal.name.split('.')[0].replace('_',' '))
        for child in animal.hyponyms():
            add_to_set(child)

    add_to_set(wn.synset('animal.n.01'))
    all_animals = list(all_animals)

    actions = ['ate','chased','killed','fought','kissed',
               'talked to','hated','loved','ambushed','fled'] # can add more

    def make_password():
        import random
        random = random.SystemRandom() # is this secure?
        choice = random.choice
        return 'the %s %s the %s'%(choice(all_animals), choice(actions), choice(all_animals))

If you pruned out 90% of the animals (i.e. the obscure, hard to spell, or scientific names), this is still about 20 bits. And the passwords are kind of memorable (I've gotten such gems as "the dodo chased the guppy" or "the tigress killed the king charles spanial").

You could also add a humorous adjective ("rabid", "talking", "magic", "invisible", "evil" ...) or adverb ("roughly", "quickly", "quietly", "secretly" ...).

You could also add a place name.

Periodic• 15 years ago

Completely random strings of words can be hard for me to remember, but something like, "the {adjective1} {animal1} {verb} the {ajective2} {verb2}" would be much easier for me to remember because the words relate to each other ways I already understand.

I expect we can get some fairly high entropy from just simple schemes like this.

However, the length of the password can be a real pain if you have to type it often, even once a day.

wisty3• 15 years ago

You could get about 8 bits per animal, and 5 bits per hand-written verb / adjective / place (32 choices per category). So that's about 7-10 words you need in the frame.

You could get decent entropy with: the {adj} {adj} {animal} {verbed} the {adj} {adj} {animal} from in {place}. That's 5+5+8+5+5+8+5 = 41 bits.

I'm just wondering if it's worth it.

kragen20• 15 years ago

This is truly awesome. You could easily use a more complicated grammar, but it might get tricky to generate a password with a specified amount of entropy.

nmcfarl• 15 years ago

I've been using phrases and sentences as passwords for a while, and I've found that there are 2 main problems;

1) A lot of sites, still in this day and age, have max password lengths, so I still have a lot of short passwords. Usually this is bank sites and the like.

2) Password entry fields are often very short visually, and with a long password getting lost is much easier. I find I have to type them over A LOT.

The second is actually the more annoying problem.

colanderman• 15 years ago

Don't forget sites that require: "your password MUST contain at least one number, one uppercase letter, and one of the following characters: !, @, #, or $, but not %, ^, &, or *". I slap my forehead at how counterproductive these requirements are.

Simucal2• 15 years ago

What could the reasoning behind those requirements possibly be?

Lexarius2• 15 years ago

This is why, for my lab's password changer, the requirement for short passwords is simply that it must have one upper, one lower, one digit, and one none-of-the-above (and be at least 8 characters).

If you have a long password (at least 16 characters), all other requirements are waived so that you can use passphrases.

andyking• 15 years ago

I have a couple of domains registered with 123-reg.

To prevent unauthorised access to your account your password must contain 8 characters.

Wait, what? They're right, too. You can't have 7 characters and you can't have 9.

flatline• 15 years ago

Especially if you are logging into multiple systems regularly using domain credentials, it rapidly becomes apparent that the faster and easier the password is to type, the better. I've found that some passwords with symbols and numbers just roll off the fingertips with a little practice, others not so much, but longer passphrases are for some reason the worst.

jarek• 15 years ago

This. My password is not a word, not even a word with substitutions, but it is optimized towards typing it on a keyboard (in terms of when caps come in, when numbers are added, switching hands, etc). I can knock it out in a second and it's muscle memory with zero risk of forgetting. correct horse battery staple, not so much. I lose some entropy by making it typing-friendly, but the cracking algorithm to simulate that would be pretty difficult. I'll take the loss.

As an aside, 1000 guesses a second? Seems generous.

dpark8• 15 years ago

These are the real issues with this. Banks seem to be borderline idiots when it comes to password security: case-insensitive, no spaces, 20-character max, small choice of "special characters". These are from Amex, who's password requirements sadly were even worse a few months ago.

With crappy password requirements, it's impossible to use decent passphrases. Getting locked out of your account for 3 failed attempts at typing a 30-character password is pretty obnoxious, too.

In situations that allow passphrases, you don't need a password generator like this. You can grab a sentence from your favorite book and use it. e.g. "How do you do, Miss Doolittle?" That's not the best choice, but it's still got way more entropy than a standard password, probably a lot more entropy more than you'll get by choosing a 4-gram composed of words from a corpus of 2k, and it's easier to remember.

kragen20• 15 years ago

It turns out that you are mistaken.

Your favorite book is almost certainly chosen from the 129 million books that Google knows about: http://www.fastcompany.com/1678254/how-many-books-are-there-...

That gives you 27 bits of entropy.

The average book length is probably not over 400 pages. An average page probably doesn't have over 25 sentences on it. So the whole book contains only ten thousand sentences.

That gives you 14 more bits of entropy.

The total is 41 bits of entropy. This is one-eighth as secure as a 4-gram composed of random words from a corpus of 2k, if we measure strictly by entropy.

The situation is actually much worse, though: your favorite book is probably a popular book. So the number of bits of entropy provided by the choice of book might be a lot smaller than 27. I would guess that it's perhaps 10.

And many of those 129 million books are not very different. They contain quotes from other books, reprinted short stories, folk tales, set phrases, and so on.

In practice I think it might be difficult to mount a password-guessing attack using the Google Books corpus, because it's hard to get access to that corpus. The Project Gutenberg corpus would not be so hard.

jobu• 15 years ago

Also annoying is that a lot of sites require gibberish. Apple requires at least one uppercase, one lowercase, and one number. Some sites require a symbol as well.

ghshephard• 15 years ago

Very few sites have a short max password length. I use 1password, and of the 63 sites I've stored passwords, all but 2 allow 25 character password lengths. Ironically, my Bank only allows me 15 characters.

I haven't typed a password in 3+ months - don't know what any of mine are anymore, so I find typing is no longer an issue.

cschneid• 15 years ago

I really like using 1password. I have a long passphrase as my unlock key, easy to remember, then do the randomly generated codes as long as is feasible for each different service.

1) Nothing written down 2) Unique per service 3) Adjustable difficulty & char set per service, to match their stupid requirements.

Seems like the best of several worlds.

r00fus• 15 years ago

I just use a password manager like laspass or 1password. If it has submission automation, you don't even need to type your password.

Just choose a nice strong master password.

drcode3• 15 years ago

One slight addition to the xkcd password scheme that would add another order of magnitude of security would be to have your own personal "salt" that you add to all your passphrases. In this case, the salt would be a short, traditional, hard to remember password that you re-use with every xkcd style password. It would be hard to remember, but you'd only need to memorize it once.

So if your personal salt is "@T#23a" you would use "@T#23a correct horse battery staple" on one website and "@T#23a giant bug transistor leech" on another website.

cdavidcash• 15 years ago

You might want to read the cartoon again to see why this is useless, counterproductive advice.

dsmithn• 15 years ago

If this kind of thing takes off, it will become easier for dictionary based password attacks. Using this advice would go a long way towards preventing this.

xyzzyb• 15 years ago

Yes, but the salt could also be useful for sites that require passwords to include a number, a non alphanumeric character, etc.

re_todd• 15 years ago

That is what I do, I have a 4 character personal salt, like "7Pd$", and put it in the middle of a lowercase word or phrase. Having a symbol, lowercase letter, uppercase number, and number will satisfy most password requirements. I use it on many sites, so it is easy to remember. It also makes it simple to write passwords down, e.g. "correct horse ^ battery staple" which means to me "correct horse 7Pd$ battery staple", but would not be useful to someone who saw it, since they don't know my personal salt. A combination of what xkcd said and a short personal salt that's easy to remember is probably best.

nrbafna• 15 years ago

"For those of us pedantic enough to want a rule, here it is: The preferred form is "xkcd", all lower-case. In formal contexts where a lowercase word shouldn't start a sentence, 'XKCD' is an okay alternative. 'Xkcd' is frowned upon."

scythe2• 15 years ago

You could probably get a few more bits of entropy kind of easily if you use words from other languages. This doesn't help the monolingual among us but it's great for me.

kijinbear2• 15 years ago

Some Koreans do this: they just type up some Korean words. Since most password fields only accept ASCII symbols, the password gets entered as a nonsensical string of alphabets. For example, the Korean word '비밀번호' (meaning 'password'), when typed on a standard Korean keyboard, becomes 'qlalfqjsgh'.

eru6• 15 years ago

Yes, though the number of additional bits you get from increasing the size of the dictionary decreases fast. E.g. suppose English and German have the same number of words, then using both only gives you one more bit per word.

(Actually, slightly less since some words exist in both languages. Like `hell'.)

scythe2• 15 years ago

>Yes, though the number of additional bits you get from increasing the size of the dictionary decreases fast.

Well, sure -- but once you're at around two or three languages, you get to imagine that the attacker doesn't know what languages you're using. If I use English, Japanese, and Spanish, I can figure on the attacker needing to check the Germanic (English, Dutch, German), Romance (Spanish, French, Italian), and Asian (Japanese, Chinese, Korean) languages at a minimum.

Jargon helps too, and proper names. "dijkstra bicycle entonces boojum daihinmin"

Gullanian• 15 years ago

Once hackers realise people are using ~4 random words for a password the entropy will decrease hugely.

wcoenen3• 15 years ago

I think you've got it backwards: the entropy calculation here assumes that the attacker already knows the scheme. The 2^44 possible passwords are therefore a lower boundary for the entropy.

In practice the attacker must cast a wider net because he doesn't know exactly which word list you use, or if you are using a completely different password scheme. This increases the difficulty.

tantalor• 15 years ago

Sorry, but this isn't novel. I can't find it now, but I read a blog post that described this technique recently (~6 months ago).

Edit: y0ghur7_xxx (http://news.ycombinator.com/item?id=2872827) found it: http://www.baekdal.com/tips/password-security-usability

Symmetry• 15 years ago

I generally use gpw to generate long random but pronounceable passwords. Something like 'armsdaynistoppo' is fairly entropic, easy enough to remember, and when I'm used to it I can type it much faster than 4 random words.

IgorPartola3• 15 years ago

Put this in your .bashrc:

  function rpass() {
      strings /dev/urandom | grep -o '[[:alnum:]\/!@#$%^&*()<>,.,{}]' | head -n $1 | tr -d '\n'; echo
  }

Then run $ rpass 16 and get a 16 character random password with a fairly high entropy. Then just use a service like LastPass or a solution like KeePassX or even a single GPG-encrypted file to store your passwords. Problem solved.

Passwords are evil. Most of them should be treated the way you'd treat your private SSH or SSL key. Whenever you can eliminate a password and get the user to authenticate using a third-party identity provider, you are doing them a favor.

Edit: with 80 possible characters, you get 80^16 possible passwords: 10^19 years at 1000 guesses/second.

yuvadam• 15 years ago

Actually LastPass has this option built-in. It can generate a strong password in-form and directly save it to your password vault.

Very useful.

IgorPartola3• 15 years ago

Yes, but I prefer to generate the passwords on my own. I also use this to generate random passwords for root accounts (sudo FTW), etc.

duck2• 15 years ago

If you use KeePass there is no need for the script since it will generate one for you based on rules you can set.

slug• 15 years ago

or use pwgen , apg, etc

parfe• 15 years ago

1000? Try 600 million passwords a second.

http://www.elcomsoft.com/lhc.html

IgorPartola3• 15 years ago

80^16/(600 x 10^6)/(365 x 24 x 3600) = 10^14 years.

Khao2• 15 years ago

I remember wanting to sign up on a website that had the worst password "feature" ever : you typed your password in a plain textfield, and once you clicked away it was changed to a password field. Seeing as how this "feature" was on the main page I decided never to use this service and sent the website an e-mail saying that their password field is not clever but instead is a big fat counter-security measure.

Edit : I managed to find back what website it was : http://www.advirtus.com/ when you register it shows the password as you type it

CWuestefeld• 15 years ago

I think that's fantastic.

1: what purpose do the stupid asterisks serve, anyway? I understand them on an ATM machine, but not on my desktop PC or phone.

2: Very frequently (like, maybe 50% of the time) when trying to type a password on my phone, I miss the little "key" and mistype, but can't see that I did. I have to make multiple tries at entering the password. This feature would prevent that.

So it looks like all upside, with no cost (when used only in appropriate contexts).

Khao2• 15 years ago

I agree that this feature is good while working with a smartphone, but I'm pretty sure Android has a settings somewhere to always show the last letter you typed in every password field. I would be surprised if there wasn't a setting for that also on iOS.

The thing is, I think it makes perfect sense to implement this in certain situations, but at an OS or browser level, not in the website or inside an application. Passwords are something we have grown used to and we always expect them to behave the same way! If we were to change the way passwords are handled, it should be consistent across everything.

For example, browsers could implement password fields with a checkbox next to it that lets you show/hide password at your will. The fact that this website has only one setting (always show when in focus) is scaring me.

dfxm12• 15 years ago

1. Shoulder surfing a password is way easier than other forms of cracking. Sure, you might not think people are looking at you as you type your password, but then this becomes a crime of opportunity...

2. There are technological ways around this, like finding a bigger keyboard for your phone, using password management software, imploring the website to make an app, practicing typing, etc. Also, BB/iOS/Android all show the most recent character you typed in a password field. Many soft keyboards give feedback about the most recent character you types as well.

I'm fine with my password fields being obfuscated.

wcoenen3• 15 years ago

Note that 44 bits of entropy is still nothing if you want protection from off-line attacks on password hashes. A couple of GPUs together can calculate a billion hashes per second, which eats through 2^44 possible passwords in only a few hours.

This was recently demonstrated when the mtgox password database was compromised.

edit: but this shouldn't be a problem if the password is properly hashed with bcrypt or some other scheme with a work factor.

salvadors5• 15 years ago

But this approach scales at a much faster rate. Simply adding a fifth word throws even a billion-per-second attack out into hundreds-of-years territory.

dendory• 15 years ago

If you look at the source, their word list contains around 1600 words. That is just no where near enough. Using this would give you a very easy to crack password. You need to make up your own passwords with words you come up with.

eru6• 15 years ago

> You need to make up your own passwords with words you come up with.

That might have even less entropy. Why not just get a bigger dictionary? Most Unix systems even come with a dictionary.

kragen20• 15 years ago

1600 words is 10.6 bits per word. If you want to reach 70 bits (safe from offline attacks with custom hardware), that means you need 7 words, which is within most people's capacity to memorize. If you increase your wordlist to 65536 words, you can get 16 bits per word, but you have to include words like "lefeuvre", "aarau", and "aubagne". Then you can reach 70 bits in only 5 words. That's not worth it.

Inventing your own words is unlikely to produce very random words. You'll probably mostly invent the same few hundred nonsense words that any other speaker of your native language would invent.

In other words, you have no idea what you are talking about and should not have posted.

salvadors5• 15 years ago

On what basis is that "very easy"? Four words from 1600 is 1600^4 permutations, which would take over 200 years to test at a 1000/second attack.

Sure, if we're talking about a different type of password, and 2-billion-tries-per-second attacks, it'll fall in about an hour, but simply pushing that out to six words from that dictionary will still stymie that level of attack for a couple of hundred years. The size of the dictionary is much less important than the length of phrase you generate from it.

nikcub3• 15 years ago

as a bash alias:

  word_pass() {
      cat /usr/share/dict/words | awk 'BEGIN{srand();}{print rand()"\t"$0}' | sort -k1 -n | cut -f2 | head -n 4 | tr "\\n" " " && echo 
  }

then:

  $ word_pass
  corticifugally tetraploidy democrat vibrionic

(if you notice how this works, you can see that it isn't super-efficient, but it works)

adr_• 15 years ago

Using shuf, my favourite, rarely used gnu textutil.

    shuf /usr/share/dict/words|head -4|tr '\n' ' ';echo

nikcub3• 15 years ago

ye it isn't on OS X

just the same, sort -R is GNU only and not POSIX

gjm114• 15 years ago

DANGER: This gives no more entropy than what srand() uses, which (at least for GNU awk) is simply the current UNIX time, which (if we assume that when you generated the password is known to within one year) means only about 25 bits of entropy.

nikcub3• 15 years ago

srand in awk is platform specific. on most recent is isn't a straight call to srand().

I have another version that I use that stuffs srand but in the end I figured srand from a 250k dictionary is still better than picking words out of your head from a ~1k dictionary

billybob2• 15 years ago

Example generated phrase: "married greatly snake battle"

These phrases would be easier to remember if they made grammatical sense. Like Chomsky's famous "colorless green ideas sleep furiously" - the words relate to each other grammatically, even though it makes no sense.

Imagine memorizing "married greatly snake battle" vs "married snakes battle greatly." I think the latter is easier.

burgerbrain8• 15 years ago

Entropy would take a serious hit if you did that.

kragen20• 15 years ago

Not necessarily. If only one-fourth of all English words are grammatical after an average prefix, then you lose two bits of entropy off each word after the first. I suspect that the actual situation is not as bad as that. You might end up using "uncommon" words like "deceased", "advent", "fearful", and "ram" to compensate, instead of more common words like "strongly", "contains", "afterwards", and "corporate", but that doesn't seem like a major loss to me.

julianpid2• 15 years ago

I find the idea incredibly stupid. If I know someone who used that precise generator to produce his password. Then I know that the generator has less than 2000 words in the dictionnary. It then takes me only a few minutes to guess his password, rather than 550 years.

Conclusion: Don't ever use this password generator, write you own, and tell no-one about it.

zokier• 15 years ago

  4b02d9f6353a8f36fbb092f040d5a31cdf6841f2

You up for a challenge? I just generated a pass phrase with this generator, and hashed it with SHA-1 (echo -n ... | sha1sum), no salting or anything else special. Feel free to brute force it.

julianpid2• 15 years ago

I wrote this piece of code: https://gist.github.com/1149417

It's currently running at 3200000 tries per second on my Xeon machine. I am probably going to get bored before I find the right combination because I calculated it could take up to 52 days. :)

But anyways, it is still a lot less time than trying to bruteforce something like Tr0ub4dor&3 in my opinion.

It seems you like challenges, if I gave you a SHA1 hash of something similar to "Tr0ub4dor&3", would you be able to crack it (without rainbow table) under 52 days ? I don't think so.

salvadors5• 15 years ago

Let's say the dictionary only has 1000 words in it. A phrase of four words in a row from that is still 1,000,000,000,000 possibilities, which is going to take you significantly more than a few minutes to work through at 1000 tries per second.

tgrass• 15 years ago

This still creates a false sense of security since it seems (and I stress seems) to implicitly suggest you can use the same password on every site (I assume this since the argument for its use is the ease of remembering). If one site you visit handles passwords in plain text and it has your email, upon a breach all your accounts are effectively compromised.

pguzmang• 15 years ago

This article is math true, however, hackers no longer use brute force attacks and the most popular method is to attack a weak website like for example a not very popular blog, then if they succesfully broke it they have a password and a email account from you and if they are very lucky you have the same password for the email account, so, they got you. Therefore, nowadays it is safer to have different passwords for every site. Personally, I love to use lastpasss for my personal use and keepass for the office to store and manage passwords. Obviously, the weakest link of the chain is my password for the password manager application. Any of you use a different password manager?

Adaptive• 15 years ago

You can add a variety of two factor authentication options to lastpass (phys OTP, yubikey).

You can also allow/disallow "offline" access to your lastpass account when using these two factor options (force second factor at all times or allow single factor if offline).

redxaxder• 15 years ago

When picking a password, you don't just care about the entropy. You also care how far down the password guessing order it is.

People who want to guess a password don't just brute force at random. They use a guessing order that goes through more common classes of password first. So if correct horse battery staple becomes a popular password scheme, these will end up attacked before other password schemes. (See http://www.schneier.com/essay-148.html)

Unless you're going to use a password safe full of nasty passwords, you should pick your passwords using an unpopular method.

salvadors5• 15 years ago

The point is that this approach pushes brute-force guesses out into territory that makes it unlikely anyone will crack it even if they know exactly what scheme you're using.

People seem to be massively underestimating just how long it would take to brute-force four dictionary words in a row.

GFischer• 15 years ago

The link posted on the article merits a submission by itself:

"The science of password selection" (a breakdown of common passwords by selection practices, as taken from public leaks)

http://www.troyhunt.com/2011/07/science-of-password-selectio...

In short, passwords are chosen from:

People names: this includes a list of about 26,000 common first and last names.

Place names: this is everything from towns to states to countries and includes about 32,000 entries.

English dictionary

The most common passwords by group:

Name:

   1. maggie
   2. michael
   3. jennifer

Place:

   1. dallas
   2. canada
   3. boston

Dictionary Words:

   1. password (oh dear)
   2. monkey
   3. dragon

Numbers:

   1. 123456
   2. 12345678
   3. 123456789

kragen20• 15 years ago

Is it possible that the breached Sony passwords he was analyzing may have been cracked with dictionary attacks? Maybe the reason only 1% of the passwords had a non-alphanumeric character was that the crackers mostly didn't crack the passwords that had any non-alphanumeric characters.

numeromancer• 15 years ago

What a great article! I'm changing all my passwords to "correct horse battery staple" today!

kingsley_20• 15 years ago

If you're bi-lingual in a non-european language, transliterating obscure phrases from the other language could work well. For example, the poetic title திரிகூடராசப்பகவிராயர் would transliterate to thirikUdarAsappaKavirAyar. Add some subs & punctuations and I'm done - very rememberable (at least for me) :).

pedro_a7• 15 years ago

Assuming there are 1024 languages in the world you added 10 bits of entropy. That can be achieved adding an extra common word.

absentbird• 15 years ago

This is how I come up with passwords; I find a phrase that I can remember without too much trouble then I use the first letter of each word to make a password.

Phrase: Three Rings for the Elven-kings under the sky, Seven for the Dwarf-lords in their halls of stone

Password: 3RftE-kuts,7ftD-lithos

Easy to remember and highly secure. I have been using this method for years.

Bonus example: Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty

4sasyaofbfotc,ann,ciL

Less secure then the last example but still strong. Especially if you use uncommon strings like the words to a song by a local band or a phrase from the newspaper or an unpopular book. That way even an attack targeting this method will take a long long time.

kragen20• 15 years ago

This is probably not as secure as the xkcd scheme if you don't make up the phrase yourself. See my comment above with calculations about a variant of this scheme. I suspect that both of your example phrases are among the million most quoted phrases in the English language, giving them entropy of under 20 bits.

rubberbandage• 15 years ago

This is the same method Apple officially recommended in their help for choosing a secure password—the example they gave was “Tnf,tfws95” (“That’s not flying, that’s falling with style”) followed by the year of Toy Story’s release (where the quote is from). I agree that it’s an excellent combo of passphrase and obfuscation. Unfortunately, their documentation now[1] gives the same kind of example that XKCD points out will be exceedingly difficult to remember correctly.

[1] http://support.apple.com/kb/HT1506

vidyesh• 15 years ago

Great so now we soon would find a xkcd-brute-force-attempt-list.txt

juanefren• 15 years ago

I have just created a spanish version, that is easier to fork to other languajes. http://dl.dropbox.com/u/1990697/pw_gen.html

dkokelley• 15 years ago

I still sense a problem. While these passwords ARE easier to remember, there is still the security flaw that most people reuse passwords. A key-logger or shoulder-surfer could snag this (or a website could store your password in plaintext and be compromised) and then it's game over. Password managers are the future. They can memorize unique passwords of any length and complexity for every website you use, and they can store the passwords with very strong encryption with 1 key that is memorized. That key is where a password like 'correcthorsebatterstaple' could be effectively used.

epscylonb• 15 years ago

This kind of misses the point.

A password doesn't necessarily need to be something that is easy to remember. It just needs to be a unique token that is easy for you personally to present when needed.

I currently use a keepass file stored in my dropbox folder. I am not certain what the silver bullet to online authentication will look like. However I suspect it may not require you to remember more than one secure password, perhaps not even that.

Trust online is hard though, looking at the problems establishing trust online reminds me how clever human beings are, we sometimes make mistakes but we are pretty good at evaluating trustworthiness in the real world.

codebot• 15 years ago

Funny comic as usual, but the 20 years thing is probably invalid. How long would cracking tr0ub4dor&3 on a 486 take? Also I remember some systems didn't allow pass phrases back then. Windows NT in particular had a max password limit of 14 characters, iirc.

kragen20• 15 years ago

Faster CPUs don't necessarily mean you get more than 1000 auth requests per second against the web site you're trying to brute force.

presto8• 15 years ago

Four English words selected randomly from a large dictionary is certainly secure. But it's unwieldy to type 20+ character passwords. I prefer 10-digit random alpha-numeric passwords, although these are hard to remember and type. Best compromise in my opinion is to use a hashing function with a moderately difficult passphrase, e.g., Site_Password = Hash( Domain_Name || Passphrase).

Dove4• 15 years ago

I find the discussion surrounding the XKCD strip alarming for the superstition it reveals about password generation. The particular theme I am alarmed by is that people seem to think that if a password looks alien, or was difficult for them to come up with, it will be hard for a machine to guess.

Look, we're working with big numbers here. You need to do the math.

In this thread alone, I've seen suggestions to use a common dictionary word translated into another language, or written in l33tsp34k with some permutations. From a probabilistic perspective, these are still dictionary words, even though they look like gibberish. The same is true of the common method of typing a word with ones fingers displaced on the keyboard.

Conversely, I see a lot of argument that these XKCD passphrases would be easy to guess because they are made up of dictionary words. This misunderstands the math behind the situation. Even if an attacker knows that your password was generated via this method, and even if they know the word list you used, the password is still hard to guess. The difficulty grows exponentially with each word in the phrase, and that's pretty fast.

The key with passwords is not to create something that looks random -- something that if you showed it to another human being, they'd have a hard time deciphering. It's to create something that is random; literally a result of a throw of the dice for every new password.

Human beings are really bad at creating randomness. There's a demonstration done in an early statistics class in which the professor divides the class into two groups. He tells one to toss a coin a hundred times and record the sequence of heads and tails, while the others are to write down a sequence they think is random using their imagination. The papers are completed and mixed and then -- magically! -- he is able to sort them into the two types, easily and with high accuracy.

The lesson is this: even when you think you're being random, you probably aren't. You're probably using the same tricks everyone else is, and making the same mistakes.

I would trust passwords that come out of a script like this to be far more secure than passwords anyone (myself included) made up, no matter how random they're trying to be.

Cushman6• 15 years ago

This should be higher up. It's scary to see people — intelligent people, I'm sure — saying things like "And that goes even higher when you add punctuation!"

No, it doesn't. All of the reasonable punctuation you could add to a sentence adds only a few bits of entropy at best. It also makes the sentence harder to remember— was there a comma or not? Adding unreasonable punctuation or symbols is even worse— you get slightly more entropy at the cost of a password that is way harder to remember.

The crucial point here is that four random words, separated by spaces, selected at random only from the 2000 most common English words — EVEN IF your attacker knows that your password is four random English words from the 2000 most common separated by spaces — already is a very long random string. If it's not random, each common English word you add adds 11 bits, and is only marginally harder for most English speakers to remember. Conversely, choosing "random" extra characters to add in makes it slightly longer, very slightly more random, and way, way harder to remember.

a3camero• 15 years ago

It's certainly a "very long random string" without context but as people have pointed out above, it's actually not a very good password if people adopted this pattern widely (and you said the attacker knows this).

2000^4 = 16000000000000 possible passwords = 1.6E13 = ([A-Z] + [a-z] + [0-9] + [!@#$%^&()])^7.1ish. So, your four words from the 2000 word list are equal to a 7ish character password that looks like "Av#12GH". I'm not sure if you meant that seven characters was "very long" but I wouldn't say it is. Still a very strong password but maybe not as random as it appears to be when the pattern is known.

keithnoizu2• 15 years ago

This is not entirely correct, we include non alphanumeric characters (punctuation) in our passwords occasionally because it increases the solution space for a brute force attack.

   While this doesn't really improve any individual password the fact that we occasionally include non alphanumeric charecters increases the possible password set from 62 possible charecters ^ password length to a something more like 90^password length.  

  Similarly we dictionary attacks are more efficient than brute force attacks because we're talking maybe 200,000^(words in password) if we allow for some common word permutations versus 90^passwordlength.

jcr• 15 years ago

I resent your accusation that I use gibberish for my passwords; I actually use perfectly well formed executable code in perl.

nakkiel3• 15 years ago

Had you used brainfuck, I would have downvoted you.

Ideka• 15 years ago

May I ask how did you find out about that study?

It sounds very interesting. I've got to try it sometime :).

Dove4• 15 years ago

You mean the statistics demonstration? I'm sure I've seen it in several places.

I know of two tricks for detecting the students. The first is to look for six or seven heads or tails in a row. Over a hundred tosses, a coin will probably do that, but humans "being random" won't. The other is to look at the page as a sequence of "HHH" and "TT" strings and estimate how many there are. A coin, of course, changes from heads to tails 50% of the time, but a human does it more like 70% of the time.

I'm sure there are other characteristics, too, but those two are sufficient to throw out most human attempts at a glance. It's actually kind of obvious, when you see the two side by side.

Me "being random" with the numpad: 10110101001010010101011010100101011010100101010110101

Computer-generated random: 1101110100000000011111110111011000010001010110011111

See? Here's a few more. Try it.

1000100111011001010000001001010110111000011011101011

1101010001010010101110100101000101010111101001001000

1101111010110111100010110001000100001001111001001110

1100000010000010101001000001101001101011111100111001

dspillett• 15 years ago

> I would trust passwords that come out of a script like this to be far more secure than passwords anyone (myself included) made up, no matter how random they're trying to be.

Definitely agree with you here.

I've been using the "few random words" method for passwords I need to remember for some time (and random 20 character mixes of alpha/numeric/symbol for the other, which I have stored in a keepass db), and I know I'm not all that random in my choice of words so if someone managed to see one or two of my passphrases it would be quite easy to create a script that could brute force the other couple quickly.

I shall have to use a script like this (or throw together my own for paranoia's sake) next time I change one of my passphrases.

Shenglong• 15 years ago

Does anyone else here not really remember their main password? Mine's all in muscle memory and I can't write it out unless I imagine a keyboard.

shinratdr2• 15 years ago

I wish that was why I didn't know my password. The real reason is that 1Password manages that part of my life for me so all my passwords are long randomly generated strings that I don't know.

shin_lao• 15 years ago

Don't forget to add "correcthorsebatterystaple" to your dictionaries kids!

abecedarius• 15 years ago

"It's a novel idea."

No, I posted about my own generator in 2005: http://darius.livejournal.com/38591.html (getting the words from Beowulf). Then Zooko or Kragen pointed out some even older system in response (I forget the name).

ajross2• 15 years ago

Compuserve was generating automatic account passwords in the early 1980's from two dictionary words and a non-alpha character in between them. Mine was "sleeve;coast". No doubt they didn't invent the trick either.

frosas• 15 years ago

How does one calculate password entropy? I deduced this one:

entropy = log2(symbols^chars)

But using 63 symbols ([a-zA-Z0-9&]) I get 65 bits for Tr0ub4d0r&3, not 28.

wcoenen3• 15 years ago

You are making the same error that led to the popularity of passwords based on a common word and some substitutions.

Your calculation is for 11 characters, each chosen completely at random out of 63 symbols. People don't chose a password that way - we typically can't generate or remember random symbols.

XKCD's calculation is for a common word + common symbol substitutions and additions: log2(#words) + log2(#capitalization options) + log2(#substitution options) + ...

kragen20• 15 years ago

You calculate password entropy of a password drawn from a set of equally likely passwords by taking the log_2 of the size of the set. (This is a convenient special case of the more general formula for entropy.) A convenient thing about this is that if you concatenate two things (in such a way that you can pull them apart again) the number of possibilities is the product of the possibilities for each of the things, so the entropy is the sum of the entropies.

ajross2• 15 years ago

I can't help but think that this is a solution to the wrong problem. The big problem with password security in the modern world really isn't that they're easy to break, but that they're pervasively reused between sites. So breaking them (for example, by reading them in plain text out of a dumb database!) in one place opens up attacks on higher value accounts.

The fix, of course, is to get users to stop re-using passwords between sites.

How does making passwords more memorable fix this? If anything, forcing users to use random base64 strings strikes me as more secure as they will be forced into some sort of password locker implementation by their inability to remember them.

crizCraig• 15 years ago

Right, maybe if you use the first letter of the words in a sentence, like "Hey Jude, don't make it bad, take a sad song, and make it better." -> "HJ,dmib,tass,amib." Then you can add in some characters that make it different for each site without it being obvious which characters you added. I wrote a blog post on how to create different passwords for sites that are easy to remember: http://craigquiter.com/post/8668237043/creating-and-remember...

aidenn0• 15 years ago

Watch out for sites that only use the first 8 characters of your password (no matter how long it is).

raleec• 15 years ago

Or those that ignore case... I've come across a few popular ones that do that!

pedro_a7• 15 years ago

Case is only 8 more bits assuming you randomly assign case to all of your letters. More likely it will be only one more bit. Then requiring an extra character is equally good.

abalone• 15 years ago

This scheme could be easily guessed by a dictionary attack that simply ran through combinations of dictionary words instead of individual characters.

If this became a popular scheme, the whole entropy argument goes out the door. It only has more entropy if we compare the two schemes on a character-by-character basis (~10 vs. ~25). Of course the longer string will appear to have more entropy.

But if a password guesser expects the pattern of the "four common words" scheme, as they might if it became popular, it's not nearly as entropic. A better comparison would be to consider each word as a single "character" from a 180,000 sized alphabet (for an English dictionary).

Calculate the entropy of that and you'll find it's in the same ballpark.

kragen20• 15 years ago

If you took the suggestion in your last sentence instead of offering it to the rest of us, you would see that the entire rest of your comment is incorrect.

marze• 15 years ago

Isn't this discussion premised on a server configured to allow fast password guessing indefinitely?

This is 2011, shouldn't every server be configured to allow a guess every two seconds for 20 guesses, then every 10 minutes, or something similar?

I'm not familiar with common practices in this area, but why wouldn't all such services be configured to limit the incorrect guesses?

ry0ohki• 15 years ago

Most really strong systems lock an account after a couple of incorrect guesses. I assume this is all for systems that may not be secured to prevent brute force.

mtogo2• 15 years ago

Locking the account is the wrong way to go about it since it makes DoS on known accounts trivial.

Blocking the IP or an increasing time between tries is, afaik, the "right way".

alanh4• 15 years ago

Careful! This is only using `Math.random` and does not attempt to use `window.crypto.random` (though most browsers do not support it yet: http://jsfiddle.net/alanhogan/trUYu/) or anything that would attempt to bring real entropy into the process.

I don’t mean to fault the creator of this page, but at the same time, I would not trust this generator for important passwords, simply because you cannot know if others are getting the same 'random' results as you are.

More info on SO: http://stackoverflow.com/questions/5651789/is-math-random-cr...

PDF on the topic: http://www.trusteer.com/sites/default/files/Temporary_User_T...

> In the Javascript engines of IE (Trident), Firefox (Gecko), Safari (WebKit) and Chrome (V8), the output of Math.random() can be used to reconstruct the random seed, and thus provide both this seed and the current “JS mileage” (i.e. the number of times Math.random() was invoked).

kragen20• 15 years ago

I wouldn't use a JS program served from somebody else's website to generate my password anyway. How do I know it's not sending them a copy of the passwords it generates?

alanh4• 15 years ago

Well, I watched network connections and saw none. Do that + use Incognito mode = you're probably good.

ssapkota• 15 years ago

I blogged on the same issue almost 2 months back: http://goo.gl/4Sxf6

Aloisius• 15 years ago

Personally I think password entry should be done in madlib form. Each user would have a unique madlib prompt like:

Username: ___________

Password: Twelve ___(pl. noun)___ jumped over a ___(adjective)___ ___(noun)___ named ___(proper noun)___.

ErikRogneby• 15 years ago

Amazon has implemented this. It's called payPhrase: https://www.amazon.com/gp/payphrase/claim/select-phrase.html

ryanelkins• 15 years ago

I just hate sites that won't accept spaces and restrict how long a password can be (usually to something relatively short like 8 or 12 characters). Also, many require you to use mixed case and/or numbers or "special" characters. I usually just use complete sentences.

harshpotatoes• 15 years ago

It's a good idea, and would work well, if only websites would let me choose passwords longer than 12 characters!

pedro_a7• 15 years ago

Randall is saying exactly that: Through 20 years of effort, we've successfully trained everyone to use passwords that are hard for humans to remember, but easy for computers to guess

tucosan• 15 years ago

as embarrassing as it may seem, although having read the good part of this thread, i still don't understand why a four word password, can be more random than something i would get like this:

    ~$ pwgen -s 8 C0olz5KM

Would anybody care to explain this to me, or at least point me to a good place where i can read up on this?

kragen20• 15 years ago

Assuming pwgen isn't actually defective (I haven't looked), you can get more entropy in a shorter password with pwgen. The above looks like 6 bits per character to me, so 48 bits in all. That's 4 bits greater --- 16 times better --- than Randall's estimate for "correct horse battery staple", which is much longer. But "correct horse battery staple office" gets you up to 55 bits. Is it going to be easier to remember "correct horse battery staple office" or "C0olz5KM"? And how about typing them without making errors?

xkcdentropy5• 15 years ago

The XKCD comic is only partially correct. Depending on what source you believe English text has about 0.6 to 2.3 bits of entropy per character. This means you need somewhere between 4.7 and 18.3 characters in each word to reach 11 bits of entropy per word. Assuming entropy is closer to 2 bits per character this is a realistic situation. However, when you assume entropy is closer to 1 bit per character the words have to be too long to be realistic.

redslazer• 15 years ago

I tried to generate all possible permutations of 4 of the 2000 most popular words in the English language.

My computer failed miserable after about 2000000 permutations and considering there is 10^13, i wont be making a rainbow table for this new type of password.

mathattack• 15 years ago

The beauty of this discussion is not just "How to create memorable but hard to break password?" but "How much deep insight can a 4-6 frame cartoon contain?"

The signal to noise ratio of xkcd is fantastic! They've again zipped a great discussion in just a few frames.

Xkcd Password Generator

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