AES-256 Encryption and File names encryption with 7-Zip (7z)

If you need to safely backup some of your confidential files (email, financial info, marketing info, source code,…), you can use 7-Zip (aka 7z) to compress and encrypt your archive with AES-256 as well as hide the name of the files. This should give you the level of security used by the (in-)famous insurance file (insurance.aes256) released by Wikileaks last year (if it indeed has been encrypted with AES-256).

7-Zip is available for Windows, Linux (multiple architectures) and Mac OS. Since 7-Zip source code is open, it can theoretically be ported to any platform.

The first thing I did was to use a Password Generator to get a 256-bit key such as DFF61FFB56B26158718457E5E47F3511080130C855C8E6F689A3A7664EBE2C9A.

In this example, I backup “My Documents” directory in Windows, but the same command line (just different paths) could be used in Linux as well:

Here’s the description of the parameters in the command line:

• a – Used to Add files to archive
• -t7z – Sets the type of archive to 7z
• mydoc_backup_22022011.7z – File name of the archive
• “C:\Documents and Settings\Jean-Luc\My Documents” – Folder to backup
• -xr!*BitTorrent*\ -xr!*Cache*\ – -xr! is used to exclude directories. In that case, I excluded BitTorrent downloads and all cache directories.
• -pDFF61FFB56B26158718457E5E47F3511080130C855C8E6F689A3A7664EBE2C9A – Instructs 7z to use the password after -p
• -mhe – Encrypts archive header (This will hide the file names inside the archive)
• -v4480m – Split to volumes of 4480 Megabytes to save to DVD.
• -mx9 – Ultra Compression (Optional here, ignore this settings if you have a slow computer or many files).

For further options, have a look at 7-Zip manpage.

Jean-Luc Aufranc (CNXSoft)

Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.

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