Data Hiding/Embedding
Data hiding/embedding is a cruder form of Steganography that relies on not being noticed/looked for in the first place while true steganography tries to remain hidden even when actively being looked for.
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JPEG
There are two main approaches to embedding data in a JPEG file: using the EXIF headers or appending it after the end of image marker (FF D9)
A common tactic is to manually append a zip/rar file to the end of a JPEG. The resulting file will still open as a regular JPEG in any image program, but any archiver will automatically detect and open zip/rar part.
In DOS/Windows command line, files can be appended by using the command:
copy /b host.jpg + hidden.zip combined.jpg
In Linux/Mac the command looks like:
$ cat host.jpg hidden.zip > combined.jpg
Links
- Under the hood: Hiding data in JPEG images
- Malware Hidden Inside JPG EXIF Headers
- GG-AESY - implements both methods of hiding data
PDF allows embedding complete files in the actual PDF file.
PDF allows adding arbitrary objects anywhere (or almost anywhere) in the file.
PDF allows writing data between objects
PDF allows adding for example white text on a white background or text behind other objects.
Adobe's PDF spec allows at least 1K of fluff after the %%EOF marker (although ISO 32000 does not).
Links
MP3
MP3 files are fairly tolerant of random data being added to the file, so the same file appending strategies for JPEGs can be used.
See also: MP3 wrapper
