Encrypted File System (EFS) is a secure way to encrypt files and folders on your workstation (or server). EFS is pretty much uncrackable due to the way files are encrypted. EFS encryption keys are generated on the fly to encrypt the file.

The File Encryption Key (FEK) is encrypted along with the EFS public key and is combined with the file adding an called the Data Decryption Field (DDF). To decrypt the FEK, you must have the matching EFS private key from the public/private pair. Once FEK is decrypted it is used to decrypt the file. Using Cipher.exe, you can quickly export your key, which you can put on a USB drive or a floppy for safe keeping. Run the following command to begin the export.  

cipher.exe /X

You will be prompted with a warning message, click OK to proceed. Enter a name for the backup file, and a password to protect the file with. Finally confirm the password and the certificate will be exported.

Place the PFX file on removeable media and place it in a safe and secure location.