Assuming that someone has a Mac and uses FileVault 2 FDE (256-bit AES key) and uses the BoxCryptor (256-bit AES key) for the clouds like Dropbox/GDrive/etc and or some other folders.
FileVault 2 uses AES with 256-bit keys and FileVault 2 encrypt the FDE while the system is halted.
BoxCryptor uses AES with 256-bit key and from a search on the internet it uses CBC as block chipher. Also, BoxCryptor decrypt and encrypt on user demand. So, the user asks to decrypt it a file and the files are not auto-decrypted while the system is up like the FileVault2 (correct me if I am wrong about that by the way).
Also, both of them have a different public and private keys due to the fact the "initialized passwords" were completely different.
In this case,
Let's take the following example:
- User: Turn on the Mac and login into his account.
- FileVault 2: Decrypt the whole disk.
- User: Open the Boxcryptor and encrypt a file:
textfile.txton the "Dropbox" folder
- User: Ask the Mac to be shutdown.
- FileVault 2: Encrypt again all the files. So, it encrypts again the
already encypted file:
textfile.txtfrom the BoxCryptor.
- Mac: It is powered off.
When the User turns on the Mac again, and FileVault 2 decrypts all the disk files, Is it possible to harm the already encrypted BoxCryptor file
textfile.txtwhich is located in the "Dropbox" folder ?
So, as you imagine, the question is about:
a double AES encryption with different keys and I think with different chipher blocks as well.
P.S. I dont know what chipher block FileVault 2 uses. Sorry. If someone knows about it, just edit the the question to provide more information about that.
P.S.2 Also, I saw a couple of good questions in the security.stackexchange about a double encryption, but all were quite general. They had answers like: Yep, it is secure, but what about the block chiphers? what about the Initianilation Vectors? Is the private key the same or different?
That's why I am writting the whole details about the encryption methods and I am focusing only in FileVault 2 and BoxCryptor and not in general encryption.