LinkedIn and password security· @jabenninghoff
Per Thorshiem, a Norwegian security researcher, discovered a file containing 6.5 million SHA-1 unsalted password hashes posted to a Russian hacker site. The poster was requesting help cracking the passwords. Multiple researchers have confirmed that at least some of the passwords are from LinkedIn, by looking for known passwords (i.e. their own) that are only used for LinkedIn, and by examining some of the already-cracked passwords, many of which include the words “link” or “LinkedIn.” The file appears to only contain passwords, and no usernames, but it’s likely the hacker(s) that posted the file have usernames as well. 300,000 have already been cracked.
What does this mean?
Passwords are most often stored as a hash, which transforms the password into a fixed-length value. To check if someone enters the correct password, the system takes the password entered, hashes it, and compares it to the stored hash. If they match, the system allows the login to proceed. In some cases, a salt is added to the password before the hash is done, which makes cracking harder. The salt is a random value that’s stored with the password hash.
The transformation method, in this case SHA-1, encodes passwords is such a way that the only practical method to crack the password is to calculate the hash for a possible password, and compare the hash against the list of 6.5 million. Hackers and security professionals use two methods for cracking: a dictionary attack, which tries a list of words and common passwords, and a brute-force attack, which simply tries each possible password, (aaaaaaaa, then aaaaaaab, …).
Although this may sound difficult, modern software, combined with a fast video graphics card (to do the calculations), can test hundreds of millions of passwords per second against the entire list simultaneously… combine this with the knowledge that humans choose predictable passwords, and passwords can be guessed quite quickly. Already, 300K passwords (about 5%) are known to have already been cracked. Over time, the number of cracked passwords will steadily increase.
What should I do now?
If you use LinkedIn, change your password now. It’s not certain that your password has been or even will be cracked, but it’s a reasonable precaution. If your LinkedIn password is the same as the one you use on other sites, you’ll need to change those too. A common tactic today is to try an already-known password on other sites. See my suggestions below on how I manage my own passwords for how you can make this easier for you and harder for the bad guys.
How can I protect myself against this type of attack?
The standard advice from security professionals is to pick hard to guess “strong” passwords, and pick different passwords for each site you use. This quickly becomes an impossible task; I have well over 100 passwords to keep track of. Some time ago, I gave up on trying to remember passwords and adopted a password manager. A good password manager does the job of both generating unique, random passwords for each site you use, storing them securely, all protected by a single master password, and makes it easy to enter your password when logging on to a website (just click a button!)
Right now, I use 1Password, but also recommend LastPass. I use a very long pass phrase for my master password, which is a phrase or complete sentence that should be easy to remember, but hard to guess. Five or more words is good, and using spaces and punctuation is also good. 1Password has a post that discusses the topic in detail, and I like their example of “I have 35 bats: Larry, Moe & Curly.” LastPass can step up security by allowing you to add a USB device as an additional (second factor) authenticator. I currently don’t have my pass phrase written down, but if you’re forgetful, I’d recommend writing it down, sealing it in an envelope (or a tamper-evident bag if you can get one), and storing it in a safe place, like an actual safe, or your safety deposit box.
For individual websites, I generate a 15-character random password that contains upper case, lower case, and numbers, which is compatible with most sites, and long enough that it’s really unlikely it will ever be cracked using current technology. I don’t use the 1Password built-in generator, but for those who do (it’s easier), I’d recommend setting length to 15 or more, with 1 digit, and 1 symbol for sites that require it. Since 1Password has clients for all my devices, and syncs using Dropbox, I always have my passwords handy.
The net effect of all of this? It’s easier for me to use, since I only have to remember one password that I don’t need to change. It’s harder for the bad guys, since if they manage to steal a site’s password database, they probably won’t be able to crack my password, unless the site is not properly protecting passwords and storing them in plain text. Finally, if I do find out a site has been broken into, fixing the problem is easy: I generate a new password for that site.
For security professionals:
Security professionals I know routinely use the same approach (password managers). My challenge to the community is this: why not adopt this approach for ALL passwords, including the passwords we’re charged to protect? After all, LastPass offers an enterprise edition that solves many of the problems that make passwords insecure. I’d love to hear from you via Twitter (@transvasive) what you think of giving password managers to everyone in your organization: good idea? crazy? something you’ve already implemented? I hope to write more on this topic in the future, and will include what you have to say (with attribution).