From St. Louis Hackerspace Wiki
DOS (or Disk Operating System or Dynamic Operating System) is a shorthand term for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.
Since Microsoft Vista, Microsoft has opted to use a new proprietary program called PowerShell, which has been about as warmly accepted by programmers as a wet Q-tip in the ear.
Older programmers and more experienced programmers still like using DOS to write Batch Files (.bat) to execute various scripts in the DOS Prompt.
Launching a DOS Command Prompt
Despite the fact that Microsoft has just about abandoned MS-DOS, it is still there and is as still relevant today as it has been to previous generations of computer geeks.
The fastest way to open up a Command Prompt is to key WINDOW KEY+R, which launches the Run Prompt, then type cmd or cmd.exe.
Commands you should know
|Command||What it does||UNIX equivalent|
|help||Display documentation of various commands used in DOS.||help, man, info|
|doskey||Enhances DOS by allowing arrow keys to be used to scroll through past commands used. Generally enabled, but if not, you may want to type this command. It also allows you to use the tab key to complete entering arguments as well as scroll through them using the tab key.||None.|
|cd||Change Directory. Remember, Windows uses backslashes \.||cd|
|copy||Copies one or more files to another location.||cp|
|date||Display or set the date.||date|
|del||Deletes one or more files||rm|
|dir||Displays a list of the files and subdirectories in a directory.||ls or more specifically ls -l|
|echo||Displays messages, or toggles command echoing||echo|
|mkdir||Create a directory||mkdir|
|more||Display output one screen at a time.||more, less|
|move||Move one or more files from one directory to another.||mv|
|ren||Rename a file or files.||mv|
|rmdir||Remove a directory. (Use with caution!)||rmdir|
|type||Displays the contents of a text file.||cat|
There are other commands, but the ones listed in the table above are probably the most important to know.
Using DOS to hide files inside images
A simple hack that one can do with DOS is hide files inside of images. For example, suppose you wanted to hide a secret file inside an image. You would want to do the following.
- Compress the file into a .zip either using Windows Explorer or 7-zip. We will refere to the secret file as Secret.zip
- Take an image (preferilby .jpg) and copy or save it to the directory that Secret.zip is in.
- In the DOS Command Prompt, type the following command.
copy /b Image.jpg + Secret.zip Image.jpg
In 7-zip (NOT WINDOWS EXPLORER!), go to the directory that Image.jpg is in, then double click on Image.jpg. Windows Explorer would show you the image, but in the case of Image.jpg, you can see the contents of Secret.zip hidden inside of Image.jpg.
Keep in mind that .zip compression is not the best way to use this hack. Using .tar.gz, .tar.bz2 or .7z would be recommended. Using different compression format, you can hid the same file without overly increasing Image.jpg's file size. YMMV.
How it works
The command you used in step three uses the copy command to copy a binary file (/b) by appending Secret.zip to the end of Image.jpg (Image.jpg + Secret.zip) then save it as Image.jpg.