One of the things that has always bothered me about the Chromium project (the project the Google Chrome browser is based on) is that passwords are encrypted, if and only if your operating system provides an authentication API through your account login. For example, on Windows, is is accomplished through the "CryptProtectData" function. This function uses your existing account credentials when logging into your computer, as a "master key" to encrypt the passwords on your hard drive. For Mac OS X, this is accomplished with Keychain, and with GNU/Linux users, KWallet if you're running KDE or GNOME Keyring if you're running GNOME.
In all those cases, your saved passwords will be encrypted before getting saved to disk. But, what if you're like me, and do not fall into any of those situations? Now, granted, GNU/Linux and BSD users (you're welcome) make up about 3% of the desktop installs.
Of that 3%, although I don't have any numbers, maybe 2/3 run GNOME or KDE. That leaves 1 out of every 100 users where Chromium is not encrypting passwords on disk by default. For me, who lands in that 1%, this is unacceptable. So, I wanted a solution.
Before I go any further, let me identify the threat and adversary. The threat is offline disk analysis. I'm going to assume that you're keeping your operating system up-to-date with the latest security patches, and that your machine is not infected with malware. Instead, I'm going to assume that after you are finished using your machine, upgrading the hardware, or a hard drive fails, that the disk is discarded. I'm further going to assume that you either can't or didn't digitally wipe or physically destroy the drive once decommissioned. So, the threat is someone getting a hold of that drive, or laptop, or computer, and imaging the drive for analysis. This means that our adversary is a global adversary- it could be anyone.
Now, the obvious solution would be to run an encrypted filesystem on that drive. dm-crypt with or without LUKS makes this possible. But, let's assume you're not running FDE. Any options? In my case, I run eCryptfs, and store the Chromium data there, symbolically linking to it from the default location.
By default, Chromium stores its passwords in ~/.config/chromium/Default/Login\ Data. This is an SQLite 3.x database, and as mentioned, the passwords are stored in plaintext. A simple solution is to create an eCryptfs private directory, and symlink the database to that location. However, Chromium also stores cookies, caches, and other data in ~/.config/chromium/ that might be worth encrypting as well. So, you can just symlink the entire ~/.config/chromium/ directory to the eCryptfs mount.
I'll assume you've already setup eCryptfs and have it mounted to ~/Private/. If not, run the "ecryptfs-setup-private" command, and follow the prompts, then run "ecryptfs-mount-private" to get it mounted to ~/Private/.
Make sure Chromium is not running and move the ~/.config/chromium/ directory to ~/Private/. Then create the necessary symlink, so Chromium does not create a new profile:
$ mv ~/.config/chromium/ ~/Private/ $ ln -s ~/Private/chromium/ ~/.config/
At this point, all your Chromium data is now stored in your eCryptfs encrypted filesystem, and Chromium will follow the symlink, reading and writing passwords in the encrypted mount. This means, no matter if using KWallet or GNOME Keyring, or nothing at all, your passwords will be always be encrypted on disk. Of course, in the SQLite 3.x database, the passwords are still in plaintext, but the database file is encrypted in eCryptfs, thus giving us our security that we're looking for.
However, there is a caveat which needs to be mentioned. The entire security of the encryption rests solely on the entropy of your eCryptfs passphrase. If that passphrase does not have sufficient entropy to withstand a sophisticated attack from a well-funded organization (our global adversary), then all bets are off. Essentially, this eCryptfs solution is acting like a "master password", and all encryption strengths rests on your ability to use a strong password defined by Shannon entropy. Current best-practice to guard against an offline password cracking attack, is to pick a password with at least 128-bits of entropy. You can use zxcvbn.js from Dropbox to estimate your passphrase entropy, which I have installed at http://ae7.st/ent/ (no, I'm not logging passphrases- save the page offline, pull your network cable and run it locally if you don't believe me).
Post a Comment