So BitLocker encrypts the entire hard drive, while EFS encrypts individual files. Is there any difference in the way that they implement the encryption? Do they both use your user account password as the encryption key? Is the encryption standard they use (AES-128/256) the same?
Once you've encrypted your entire hard drive with BitLocker, does it increase security by encrypting individual, sensitive files again with EFS? Does it then doubly encrypt that file?
Best Answer
There are several differences between BitLocker Drive Encryption and Encrypting File System (EFS). BitLocker is designed to help protect all of the personal and system files on the drive Windows is installed on (the operating system drive) if your computer is stolen, or if unauthorized users try to access the computer. You can also use BitLocker to encrypt all files on fixed data drives (such as internal hard drives) and use BitLocker To Go to encrypt files on removable data drives (such as external hard drives or USB flash drives). EFS is used to help protect individual files on any drive on a per-user basis. The table below shows the main differences between BitLocker and EFS.
refer the link for more detail:
http://windows.microsoft.com/en-in/windows7/whats-the-difference-between-bitlocker-drive-encryption-and-encrypting-file-system