Dropbox has developed itself as an innovative and very useful file synchronization service across all possible platforms. They also take the security of your files seriously and they are encrypted before they are sent to the cloud storage.
Dropbox is also often used to sync sensitive documents, information or password managers like KeePass across different computers. It makes good sense to take an extra step in securing them as well.
SecretSync is a freeware that works together with the Dropbox service to securely sync your files. It does this using client-side encryption, which means that before your files are added to Dropbox, they are encrypted first, on your computer.

SecretSync – How It Works:
If you use Dropbox, you know that it installs a special folder on your computer. Anything you put in that folder gets synchronized to all other computers.
SecretSync also installs a special folder, separate from Dropbox, for confidential or sensitive documents. After installing SecretSync, you will have two folders on your computer, the SecretSync folder and the Dropbox folder.

If you have sensitive or confidential documents, put them in the SecretSync folder. SecretSync detects the new file, encrypts it, and adds it to Dropbox, in a special "tunnel" folder. Dropbox then synchronizes the encrypted file to your other computers.
If SecretSync is also installed on your other computers, it will detect that Dropbox has updated files in the SecretSync "tunnel" folder, decrypt them, and add them to the SecretSync folder on those computers.
Accessing SecretSync On Your PC:
After you’ve installed SecretSync, you’ll want to access the SecretSync folder to add files. There are several shortcuts installed to get to it.
You can always access it from the Start Menu (Windows) by going to the SecretSync menu item:

Also, a shortcut is added automatically under My Documents, and optionally, on the Desktop.
Keep in mind that the SecretSync folder is just a folder on your computer like any other, so you can create shortcuts to it however you like. We like to have it pinned to the Start Menu for easy access!
Syncing multiple computers
The big advantage of sync is that it keeps files updated on more than one computer, with little effort on your part. SecretSync was designed to do this while ensuring that your data never goes online without being encrypted first.
To sync multiple computers, you will need to install SecretSync on all the computers you are currently keeping in sync with Dropbox.
On the first installation of SecretSync, you’ll need to sign-up for an encryption key. Just check the "I do not have an account for SecretSync" checkbox, enter your email, and confirm a password.

On the remaining installations, enter the account information from the first install.

This is important! If you enter a different account, it will get the wrong key, and will not be able to decrypt your data. Or worse, it will corrupt your data because it’s using different keys!
Checking and getting Java on your computer:
SecretSync was built in Java. So you’ll need to have Java installed on your computer first. The software will ask you check the version of JAVA on your PC. Follow the steps as directed.
Setting a client-side passphrase:
During installation, you will be prompted to enter an optional passphrase. This is a secret that only you know, and is stored only on your computer.

Using a passphrase in addition to the strong, randomly generated key we provide gives you an extra level of security, since no one knows the passphrase but you. However, it also adds an extra level of inconvenience.
Whatever passphrase you pick must be remembered by you. If you forget or lose this passphrase, it cannot be recovered by the service. So make sure, you keep it written somewhere.
Also, you must use the same passphrase for every install, when you install it on other computers, otherwise the files will be corrupted as they are synchronized between computers.
If you initially installed SecretSync without a passphrase, or want to change your passphrase, you will need to (1) Copy all your data out of the SecretSync folder (2) Uninstall SecretSync from all your computers, and (3) Re-install with the new key.
We recommend using this setting if you are an advanced user. If you don’t specify a passphrase, you still get the benefit of client-side encryption, as well as separation of key from data: Dropbox stores your data, while SecretSync stores your key.
Checking the synchronization changes:
Included with SecretSync is a log viewer that lets you check and see what files or folders SecretSync has encrypted and synchronized.
On Windows, go to Start –> SecretSync, and select SecretSync Log. You’ll get the following viewer. You can stop or start synchronization from this window as well.

Conclusion:
SecretSync gives you an extra layer of protection when confidential information is synched across computers using Dropbox.
If you are security conscious and also use Dropbox for storing important documents and sync them across computers, using SecretSync makes perfect sense.
Download Secret Sync for Dropbox.