In a company, all files which are sent on the network are automatically encrypted by using AES-128 in CBC mode. A fixed key is used, and the IV is changed once per day. The network encryption is file-based, so that the IV is used at the beginning of every file. You managed to spy out the fixed AES-128 key, but do not know the recent IV. Today, you were able to eavesdrop two different files, one with unidentified content and one which is known to be an automatically generated temporary file and only contains the value 0xFF. Briefly describe how it is possible to obtain the unknown initialization vector and how you are able to determine the content of the unknown file.