I want to store highly critical documents on a cloud storage as an additional backup. I am using boxcryptor which encrypts files before these get synced to cloud. Boxcryptor encrypts files using AES-256 cipher.
I am using a cloud storage service which encrypts the data at the client before storing on the cloud. So data remains encrypted at rest also. This service also uses AES-256.
Does dual encryption weakens the security?
== Edited ==
Keys are different.