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Steganography

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Definition Edit

Steganography (also referred to as digital fingerprinting or digital watermarking) is "the art and science of communicating in a way that hides the existence of the communication."[1]

Overview Edit

The term "steganography" is derived from the Greek for "hidden-writing."

Steganographic techniques can encode digitized information with attributes that cannot be disassociated from the file that contains that information. This field of technology has been termed steganography and been conceptually referred to as "digital fingerprinting" or "digital watermarking."

The advantage of steganography over encryption is that law enforcement authorities readily recognize encrypted files and are willing to dedicate resources to attempt decryption, while with steganography, police are unlikely even to realize that a hidden file exists.[2]

How it works Edit

Using steganographic techniques, a party can embed hidden messages in digitized visual or audio data. The embedded information does not degrade or otherwise interfere with the audio or visual quality of the work. Instead, the embedded information can only be detected if specifically sought out.

It also can be used to hide a file inside another file. For example, a child pornography image can be hidden inside another graphic image file, audio file, or other file format.

More advanced steganographic techniques based on statistical or entropically-directed encoding are proving to be difficult to defeat. For example, one system modulates a known noise signal with the information to be embedded and adds the "scaled" signal to the original data. Once encoded in this fashion, the steganographically encoded identification data is distributed throughout the work as subliminal noise and, like noise, cannot be fully eliminated from the work. Thus, one can ensure detection of an embedded message even after substantial corruption of the data, such as might occur through compression/decompression, encoding, alteration or excerpting of the original data. By providing a means to indelibly tag a work with specific information, steganography is likely to play a complementary role to encryption as well as authentication techniques based on digital signatures.'

Steganography does not just scramble information like cryptography does. When cryptography is used, there remains evidence that a file exists, though the contents of that file may be illegible. With steganography, the information is hidden inside of another file. Potential evidence remains virtually unobtainable. Without the correct program to unhide the information, or having the original cover image that was used before embedding (for comparison purposes), there is no indication that the file is anything other than it appears. Steganographic images have a great capacity in which to hide contraband images or illicit data.

References Edit

  1. NIST Special Publication 800-72, Glossary, at 59.
  2. Countering the Use of the Internet for Terrorist Purposes: Legal and Technical Aspects, at 26.

Source Edit

See also Edit

External resources Edit

  • Gary C. Kessler, "An Overview of Steganography for the Computer Forensics Examiner" (Feb. 2004, updated June 2011) (full-text).
  • Gary C. Kessler, "Steganography: Hiding Data Within Data" (Sept. 2001) (full-text).

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