IT’S GETTING EASIER to secure your digital privacy. iPhones now encrypt a great deal of personal information; hard drives on Mac and Windows 8.1 computers are now automatically locked down; even Facebook, which made a fortune on open sharing, is providing end-to-end encryption in the chat tool WhatsApp. But none of this technology offers as much protection as you may think if you don’t know how to come up with a good passphrase.
A passphrase is like a password, but longer and more secure. In essence, it’s an encryption key that you memorize. Once you start caring more deeply about your privacy and improving your computer security habits, one of the first roadblocks you’ll run into is having to create a passphrase. You can’t secure much without one.
For example, when you encrypt your hard drive, a USB stick, or a document on your computer, the disk encryption is often only as strong as your passphrase. If you use a password database, or the password-saving feature in your web browser, you’ll want to set a strong master passphrase to protect them. If you want to encrypt your email with PGP, you protect your private key with a passphrase. In his first email to Laura Poitras, Edward Snowden wrote, “Please confirm that no one has ever had a copy of your private key and that it uses a strong passphrase. Assume your adversary is capable of one trillion guesses per second.”
In this post, I outline a simple way to come up with easy-to-memorize but very secure passphrases. It’s the latest entry in an ongoing series of stories offering solutions — partial and imperfect but useful solutions — to the many surveillance-related problems we aggressively report about here at The Intercept.
It turns out, coming up with a good passphrase by just thinking of one is incredibly hard, and if your adversary really is capable of one trillion guesses per second, you’ll probably do a bad job of it. If you use an entirely random sequence of characters it might be very secure, but it’s also agonizing to memorize (and honestly, a waste of brain power).
But luckily this usability/security trade-off doesn’t have to exist. There is a method for generating passphrases that are both impossible for even the most powerful attackers to guess, yet very possible for humans to memorize. The method is called Diceware, and it’s based on some simple math.
Your secret password trick probably isn’t very clever
People often pick some phrase from pop culture — favorite lyrics from a song or a favorite line from a movie or book — and slightly mangle it by changing some capitalization or adding some punctuation or using the first letter of each word from this phrase. Some of these passphrases might seem good and entirely unguessable, but it’s easy to underestimate the capabilities of those invested in guessing passphrases.
Imagine your adversary has taken the lyrics from every song ever written, the scripts from every movie and TV show, the text from every book ever digitized and every page on Wikipedia, in every language, and used that as a basis for their guess list. Will your passphrase still survive?
If you created your passphrase by just trying to think of a good one, there’s a pretty high chance that it’s not good enough to stand up against the might of a spy agency. For example, you might come up with “To be or not to be/ THAT is the Question?” If so, I can guarantee that you are not the first person to use this slightly mangled classic Shakespeare quote as your passphrase, and attackers know this.
Printable Password Game Cards
The reason the Shakespeare quote sucks as a passphrase is that it lacks something called entropy. You can think of entropy as randomness, and it’s one of the most important concepts in cryptography. It turns out humans are a species of patterns, and they are incapable of doing anything in a truly random fashion.
Even if you don’t use a quote, but instead make up a phrase off the top of your head, your phrase will still be far from random because language is predictable. As one research paper on the topic states, “users aren’t able to choose phrases made of completely random words, but are influenced by the probability of a phrase occurring in natural language,” meaning that user-chosen passphrases don’t contain as much entropy as you think they might. Your brain tends to continue using common idioms and rules of grammar that reduce randomness. For example, it disproportionately decides to follow an adverb with a verb and vice versa, or, to cite one actual case from the aforementioned research paper, to put the word “fest” after the word “sausage.”
Passphrases that come from pop culture, facts about your life, or anything that comes directly from your mind are much weaker than passphrases that are imbued with actual entropy, collected from nature.
This short but enlightening video from Khan Academy’s free online cryptography class illustrates the point well.
Make a secure passphrase with Diceware
Once you’ve admitted that your old passphrases aren’t as secure as you imagined them to be, you’re ready for the Diceware technique.
First, grab a copy of the Diceware word list, which contains 7,776 English words — 37 pages for those of you printing at home. You’ll notice that next to each word is a five-digit number, with each digit between 1 and 6. Here’s a small excerpt from the word list:
Now grab some six-sided dice (yes, actual real physical dice) and roll them several times, writing down the numbers that you get. You’ll need a total of five dice rolls to come up with the first word in your passphrase. What you’re doing here is generating entropy, extracting true randomness from nature and turning it into numbers.
If you roll the number two, then four, then four again, then six, then three, and then look up in the Diceware word list 24463, you’ll see the word “epic.” That will be the first word in your passphrase. Now repeat. You want to come up with a seven-word passphrase if you’re worried about the NSA or Chinese spies someday trying to guess it (more on the logic behind this number below).
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Using Diceware, you end up with passphrases that look like “cap liz donna demon self,” “bang vivo thread duct knob train,” and “brig alert rope welsh foss rang orb.” If you want a stronger passphrase you can use more words; if a weaker passphrase is OK for your purpose you can use less words.
How strong are Diceware passphrases?
The strength of a Diceword passphrase depends on how many words it contains. If you choose one word (out of a list of 7,776 words), an attacker has a one in 7,776 chance of guessing your word on the first try. To guess your word it will take an attacker at least one try, at most 7,776 tries, and on average 3,888 tries (because there’s a 50 percent chance that an attacker will guess your word by the time they are halfway through the word list).
But if you choose two words for your passphrase, the size of the list of possible passphrases increases exponentially. There’s still a one in 7,776 chance of guessing your first word correctly, but for each first word there’s also a one in 7,776 chance of guessing the second word correctly, and the attacker won’t know if the first word is correct without guessing the entire passphrase.
This means that with two words, there are 7,7762, or 60,466,176 different potential passphrases. On average, a two-word Diceware passphrase could be guessed after the first 30 million tries. And a five-word passphrase, which would have 7,7765 possible passphrases, could be guessed after an average of 14 quintillion tries (a 14 with 18 zeroes).
The amount of uncertainty in a passphrase (or in an encryption key, or in any other type of information) is measured in bits of entropy. You can measure how secure your random passphrase is by how many bits of entropy it contains. Each word from the Diceware list is worth about 12.92 bits of entropy (because 212.92 is about 7,776). So if you choose seven words you’ll end up with a passphrase with about 90.5 bits of entropy (because 12.92 times seven is about 90.5).
In other words, if an attacker knows that you are using a seven-word Diceware passphrase, and they pick seven random words from the Diceware word list to guess, there is a one in 1,719,070,799,748,422,591,028,658,176 chance that they’ll pick your passphrase each try. English video songs free download.
At one trillion guesses per second — per Edward Snowden’s January 2013 warning — it would take an average of 27 million years to guess this passphrase.
Not too bad for a passphrase like “bolt vat frisky fob land hazy rigid,” which is entirely possible for most people to memorize. Compare that to “d07;oj7MgLz’%v,” a random password that contains slightly less entropy than the seven-word Diceware passphrase but is significantly more difficult to memorize.
A five-word passphrase, in contrast, would be cracked in just under six months and a six-word passphrase would take 3,505 years, on average, at a trillion guesses a second. Keeping Moore’s Law in mind, computers are constantly getting more powerful, and before long 1 trillion guesses a second might start looking slow, so it’s good to give your passphrases some security breathing room.
With a system like this, it doesn’t matter at all that the word list you’re choosing from is public. It doesn’t even matter what the words in the list are (two-letter words are just as secure as six-letter words). All that matters is how long the list of words is and that each word on the list is unique. The probability of guessing a passphrase made of these randomly chosen words gets exponentially smaller with each word you add, and using this fact it’s possible to make passphrases that can never be guessed.
Do I really have to use dice?
This is a longer discussion, but the short answer is: using physical dice will give you a much stronger guarantee that nothing went wrong. But it’s time consuming and tedious, and using a computer to generate these random numbers is almost always good enough.
Unfortunately there doesn’t appear to be user-friendly software available to help people generate Diceware passphrases, only various command-line-only Diceware projects on GitHub, which power users can check out. Stay tuned for a future post about this.
How to memorize your crazy passphrase (without going crazy)
After you’ve generated your passphrase, the next step is to commit it to memory.
I recommend that you write your new passphrase down on a piece of paper and carry it with you for as long as you need. Each time you need to type it, try typing it from memory first, but look at the paper if you need to. Assuming you type it a couple of times a day, it shouldn’t take more than two or three days before you no longer need the paper, at which point you should destroy it.
Typing your passphrase on a regular basis allows you to memorize it through a process known as spaced repetition, according to promising research into high-entropy passphrases.
Now that you know passphrases, here’s when to avoid them
Diceware passphrases are great for when you’re typing them into your computer to decrypt something locally, like your hard drive, your PGP secret key, or your password database.
You don’t so much need them for logging into a website or something else on the internet. In those situations, you get less benefit from using a high-entropy passphrase. Attackers will never be able to guess a trillion times per second if each guess requires communicating with a server on the internet. In some cases, attackers will own or take over the remote server — in which case they can grab the passphrase as soon you log in and send it, regardless of how strong or weak it is cryptographically.
For logging in to websites and other servers, use a password database. I like KeePassX because it’s free, open source, cross-platform, and it never stores anything in the cloud. Then lock up all your passwords behind a master passphrase that you generate with Diceware. Use your password manager to generate and store a different random password for each website you log in to.
How we use Diceware to protect our sources
At The Intercept we run a SecureDrop server, an open source whistleblower submission system, to make it simpler and more secure for anonymous sources to get in touch with us.
When a new source visits our SecureDrop website, they get assigned a code name made up of seven random words. After submitting messages or documents, they can use this code name to log back in and check for responses from our journalists.
Under the hood, this code name not only acts as the source’s encryption passphrase, but it’s also really just a passphrase generated using the Diceware method, but with a digital cryptographically secure random number generator, rather than rolling dice. SecureDrop’s dictionary is only 6,800 words long (the developers removed some words from the original word list that could be considered offensive), making each word worth about 12.73 bits of entropy. But this is still plenty enough to make it impossible for anyone to ever simply guess a source’s code name, unless they happen to have massive computational resources and several million years.
Simple, random passphrases, in other words, are just as good at protecting the next whistleblowing spy as they are at securing your laptop. It’s a shame that we live in a world where ordinary citizens need that level of protection, but as long as we do, the Diceware system makes it possible to get CIA-level protection without going through black ops training.
Thanks to Garrett Robinson for double-checking my math and preventing me from making stupid mistakes.
Top photo: Getty Images
A good password isn't necessarily synonymous with one that's easy to remember. Good, in this context, is strong. You want a super strong password so that it's more resistant to guessing and so that it's unlikely to be found in a brute force dictionary hack.
To keep your accounts secure, make a strong password that's difficult to guess and store it in a password manager so you won't forget.
Examples of Bad Passwords
Hackers and computer intruders use automated software to submit hundreds of guesses per minute to user accounts and attempt to gain access. These tools use lists of dictionary words to sequentially guess the password. Some tools add common symbols, numbers, or signs that may be added to the password to make it more complex.
Never use password as your password. A surprising number of people make this mistake.
Dictionary hacking tools that use an English dictionary list easily find words that are contained in that dictionary. If the simple word doesn't give access to an account, the tool modifies the submission and tries other iterations of the same word.
For example, a Dictionary hacking tool would attempt these iterations of the word Dog:
- Dog
- Dogs
- Dogcatcher
- Dogcatchers
- Dogberry
- Dogberries
- Dogma
- Dogmatic
- Dogmatized
- Dog1
- Dog2
- Dog3
- Dog4
Password-guessing tools submit hundreds or thousands of words per minute. If a password is anything close to a dictionary word, it's extremely insecure. When a password does not resemble any regular word patterns, it takes longer for the repetition tool to guess it.
Passwords with personal information, such as the user's birthdate or street address, are easy targets for hackers, as well.
How to Make Your Password More Secure
The best way to create a secure password is to start with a simple password and turn it into one that's much more complex.
The table below shows examples of a simple password that is progressively made more complex. The first column lists simple words that are easy to remember and are found in the dictionary. The second column is a modification of the first column. The last column shows how the simple password is converted into one that is harder to figure out.
Here are other examples of password variations that purposely avoid using complete English word patterns:
- Dog.lov3r
- dOG.lov3r
- i7ovemydog!!
- d0gsaremybestfr13nds
- sn00pdoggyd0G
- Karm@beatsDogm@
- C@ts-and-Dogs-Living-together
Words For Password Game Printable
By injecting numbers and special characters instead of letters, these passwords take exponentially longer for a dictionary program to guess.
reader comments
143 with 86 posters participating, including story authorOne of the best ways to create a random yet memorable password is to use 'Diceware.' This involves literally rolling dice and matching the resulting numbers to a list containing 7,776 English words, each identified by a five-digit number. Five Diceware words has long been thought to provide enough security for the average user.
A five-word Dice password could be something like 'boseenricoglennlardheath' or 'mastkeithhaagquirttulip.'
List Of Words For Password Game
But five words is no longer enough, Diceware creator Arnold Reinhold wrote earlier this month. Since creating Diceware in 1995 Reinhold had recommended at least six random words for people 'with more stringent requirements and where the passphrase was being used directly to form a cryptographic key,' but for average users he had said that five would do.Now, for average users he recommends 'a passphrase with six Diceware words, or five words with one extra character chosen and placed at random.'
'I had previously written that longer Diceware passphrases might be vulnerable by about 2014,' he wrote. 'Well it's 2014. Today criminal gangs probably have access to more computing power then the NSA did when this page first appeared. So I am upping my passphrase length advice by one word.'
If you have a five-word password today, adding a random character 'will make your passphrase about a thousand time more difficult to crack. Adding a sixth word makes it 7776 times harder.'
Reinhold pointed to cracking capabilities demonstrated by password expert Jeremi Gosney, whose work is familiar to Ars readers.
Even a GPU cluster from December 2012 could, depending on the cryptographic hashing algorithm used to protect plain-text passwords, cycle through 350 billion guesses per second. Referring to that project, Reinhold wrote, 'They claim they can crack a random 8-character password in under six hours. At that speed, attacking a 5-word Diceware passphrase would take on average of 7,300 hours or 10 months to find the correct passphrase, assuming they knew you were using Diceware and developed equally efficient software designed to try only valid Diceware words.'
Further, he noted that 'Criminal gangs have built botnets from thousands of computers infected with their malware. Marshaling large numbers of these computers they control might allow them to crack a five word passphrase in a reasonable amount of time.' (Gosney's 25-GPU cluster attacked the NTLM cryptographic algorithm that Microsoft has included in every version of Windows since Server 2003. It's known to be much more vulnerable to cracking than other algorithms. Gosney's machine wouldn't perform as fast against PBKDF2, for instance.)
UPDATE: In a followup e-mail to Ars, Gosney noted that 'The figures are based on a brute-force attack that targets a single hash. Due to the nature of GPU computing, attacks that combined multiple words are potentially much slower.' At the moment, 'Since there are no tools that currently combine three or more words, we don't really know for sure how much slower it would be.'
In Reinhold's Diceware FAQ, he writes that 'Six words may be breakable by an organization with a very large budget, such as a large country's security agency. Seven words and longer are unbreakable with any known technology, but may be within the range of large organizations by around 2030. Eight words should be completely secure through 2050.'
Seven-word Diceware passwords should be considered today for some high-value systems, such as Bitcoin wallets, he wrote. 'I do not claim to be an expert on Bitcoin, but some Internet searching suggests that many Bitcoin wallets do very little key stretching. That and the fact that wallets are often used to store large sums of money, make them a very attractive target,' he wrote.
Remembering long passwords is hard, especially if you're trying to remember a lot of them. That's why security experts recommend using a password manager, which generates random passwords for websites you need to log into, requiring you to only remember one password to unlock the password management software. Diceware isn't the only method for creating a strong master password, but if it's the method you prefer, a five-word password is no longer recommended.