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It certainly would be more convenient to store my KeePass database on either S3, Dropbox, or better yet SpiderOak. My fear is having my cloud storage account compromised then having the credentials recovered by either brute force or some other attack vector. How safe is this? What risks do I need to know about?

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9 Answers 9

up vote 8 down vote accepted

It is hard to quantify exactly, but if you have the DB on a mobile device then I wouldn't say this is particularly any less secure. KeePass encrypts the DB because the file remaining secure isn't expected to be a guarantee. It's certainly preferable that the DB file not get in the wild, but if your security depends on the encrypted file remaining confidential, then you have bigger problems than whether to use cloud storage or not.

A sufficiently strong master password should prevent brute forcing at least long enough for a breach to be detected and for you to change the passwords within it. In this way, it may even be slightly preferable to having a local copy on a mobile device as someone may compromise the file if you take your eyes off your device even momentarily and it would be much harder to identify that breach occurred.

If you want to secure it even further, you can add another layer of security by encrypting the file you store in cloud storage online. The master password provides pretty good security as long as you choose a difficult to brute force password (long and truly random), but it still can't compete with an actual long encryption key. If you encrypt the file that you store online and then keep that key with you protected by a similar master password, now the online component alone is much, much harder to decrypt (likely impossible if done correctly) and if your key file gets compromised, you simply re-encrypt your online DB immediately with a new key. Your still in trouble if someone can compromise your cloud account first and get the file, but it requires two points of compromise instead of one.

Personally, I'd probably end up using my OwnCloud (which is self hosted), but I have the advantage of having my own personal web server and I realize that's not an option everyone can take advantage of. (The only reason I haven't is that I don't have a particular need to coordinate a key database in that manner.) Something public cloud based service should work as a fine second alternative though.

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A VPS is worth having for just about every security-conscious person, IMHO. Vultr, DigitalOcean, et al start at $5/mo and you can load up a VPN, OwnCloud, etc on it. – Arthur Kay Aug 20 at 20:09
Security only exists on localhost. Once you put files into a "another's" server you don't control it. The really best option is to use strong password on databases, plus a key file inside mobile or pendrive, plus a yearly change of passwords to put back any bruteforce attempt. – erm3nda Oct 4 at 21:41
@erm3nda it is true you don't control someone else's system, but you also don't fully control your own. It is a false statement to say security only exists on local host. Your pen drive is susceptible to being lost or stolen. There are sla based providers with security guarantees that let you know what they are doing. You still want to have your own protective measures (line storing the data after encrypting client side) but in some situations a third party is in a better position to fill certain security elements more securely for less cost and effort. – AJ Henderson Oct 4 at 23:20
Lossing a pendrive is not a problem if you have backup the keyfile into another site, another smarter site than just a usb physical device. There's no chance to dropbox (in example) to bruteforce my security if the files has never been on their servers. I cannot be more clear than, mix things and you're done. Never let anyone the full puzzle pieces. – erm3nda Oct 5 at 7:37
@erm3nda ah, if you were simply suggesting that you should use something you keep with you to prevent decrypting the files stored online then I agree and think we are saying the same thing. There is a question of when it is enough for your needs, but that's a personal call. – AJ Henderson Oct 5 at 12:59

I use the KeyPass-Dropbox combination. The password database is cryptographically protected using a key derived from a strong master password. Even if somebody acquires your encrypted password database through your cloud account, a strong enough master password renders brute-force attacks infeasible.

Simply put: Use a strong master password and stop worrying about this.

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The cloud is inherently untrustworthy, and files kept on it should be considered vulnerable, so you need strong encryption to protect you. KeePass offers that. However, you then need to be able to trust every client you enter your password into. If you read them on an iPhone, do you trust the platform? Do you shield your password from the cameras on the subway when you enter it, every time? How about your laptop?

You also need to consider the value of what you're protecting. Is this safeguarding your retirement funds? Your fantasy bowling league scores? Political dissention that is illegal in your country? For some cases it's simply not worth the risk of making a mistake.

So yes, as long as you trust KeePass, and trust your devices, and trust your ability to keep your master key secured, don't worry about keeping the database in Dropbox.

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Every encryption you use now, would be easy hacked in a couple of years with less than a hour of computing work. I can assure everybody that use both strong password + keyfile is the only real way. Mix digital and physical barriers. Dropbox cant read your usb pendrive. Anyone who stole your pendrive may not know your password. Mix is the key, don't let other to know your way. – erm3nda Oct 4 at 21:44

You can increase the resiliency of your KeePass database to brute force by increasing the number of PBKDF2 iterations when deriving the database encryption key from your password. You can do this in KeePass under File > Database settings > Security. Personally, I use around 5,000,000 rounds (1 s delay). Remember that mobile devices are slower.

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This is actually the best answer. In fact, what @Matrix suggests is crucial to secure a KeePass database. By default it is set to 6000 encryption rounds, which is insufficient to thwart a bruteforce attack. I don't understand why I'm the only one to upvote this answer. – dr01 Jul 14 at 9:02
@dr01 not only you. This happend also with other encryption programs, are setup to maximum speed instead of maximum security. It's so preferable to read slow but remain secure. No problem to read at 50mb/s instead 200mb/s. 50mb are for movies and mega big files, not for sensible data. – erm3nda Oct 4 at 21:48

Even if your KP database were to be compromised from Dropbox, using both a strong password, and additionally a keyfile not stored in Dropbox should give you security beyond any known means of electronic attack (as long as your devices aren't already compromised).

The keyfile should be stored in a separate secure location, such as a USB drive which you can secure physically. This provides 3 layers of protection:

  1. Dropbox account (assume low security)
  2. Your strong password (strong)
  3. Your keyfile (as secure as you make it)
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Don't forget to have two or three USB keys with the encryption key on it. Preferably in separate, trusted locations. – Arthur Kay Aug 20 at 20:07

While a strong enough cipher should be able to resist brute force attack, consider that by storing your password database in the cloud you give the potential attacker much more information than he could get from e.g. a lost phone with the same database.

Every time you modify a password, the attacker gets a new database, which he can use together with older versions in differential analysis attacks. You will need a stronger cipher to resist that, compared to simple COA. If he also happens to have one of your passwords (e.g. by cracking a poorly protected password database from one of the sites you visit), he may be able to identify that password in your database. This would open doors for KPA which may be close to trivial in case you reuse passwords.

You're also giving the attacker information about your password-related activity. He will know how often you change your passwords, and may be able to deduce which passwords you change.

So, if you decide to store your password database in a public cloud,

  1. Pick a strong encryption algorithm, resistant to differential cryptoanalysis. Make sure every password in the database is individually salted.

  2. Change the master password regularly, preferably as often as you do with your most valued password.

  3. Don't reuse passwords.

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I am a strong believer in defense in depth on this.

No matter how strong your password is, it is also one that cannot be changed.

So to protect my Keepass DB, I am using three layers:

  • The database has a strong pass phrase (not just a password). I am not using a key file because, for me, the risk of losing the key file outweighs the security benefits.
  • The database is stored on an encrypted file system (I'm using encfs. By itself, it has of course been shown to be insecure, but it still adds a layer of protection).
  • The encrypted version is uploaded to an owncloud server, running on my own hardware, and of course over HTTPS.

On why the password cannot be changed: of course you can change the password, and it will actually re-encrypt the Keepass database, but you cannot retroactively change it on old copies.

Especially (but not only) if you store the database in the cloud, you have to assume that an adversary got a hold of the database at some earlier point in time, with an old password. That may give her the information she is after.

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I would really suggest you to upload your keyfile hide as other filetype, so no one can figure out it is your key. Keyfile is intended to add physical barrier, you should never put keyfile inside same drive/service than database. Lossing your key is the same than forgetting your password, so i don't really understand why you fear about. Usually, using key is only more "work" to open files, but adds a LOT of extra security. – erm3nda Oct 4 at 21:53

If you want to be really serious about things, run Boxcryptor in conjunction with Dropbox. Boxcryptor encrypts everything at your end PRIOR to sending to Dropboxs' servers. All that's at Dropboxs end is a load of encrypted stuff. Your keepass db ends up doubly encrypted!

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If a group is able to compromise a cloud service enough to discover that you have a kdb to be cracked, they may have more motivation to plant a key logger/root kit on your personal devices. Of course, if such a group can see you downloading the software from sourceforge or an app store, they obtain similar information. In fact, this post is a much easier tip-off, so concern for this attack vector may be for individuals more paranoid than ourselves.

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I'm not sure that this is an answer. – schroeder Sep 20 '14 at 17:47

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