Cover Medium
Definition
The original, unmodified carrier file (image, audio, video, or document) into which secret data will be embedded. The cover medium is chosen to appear ordinary so that the existence of hidden data is not suspected.
- Field
- Steganography
- Common formats
- Image, audio, video, document
- Selection goal
- Appear ordinary, avoid suspicion
- Result after embedding
- Called the stego-object or stego-medium
Common questions
How does forensic detection exploit the fact that a cover medium was modified to hide data?+
Embedding data changes statistical properties of the file, such as pixel value distributions in an image or least-significant-bit patterns, in ways that steganalysis tools can flag even when the change is invisible to the eye, so examiners compare suspect files against expected statistical baselines for that file type.
Why do investigators need to identify the likely cover medium type before attempting steganalysis?+
Different formats hide data differently: image steganography often manipulates pixel bits, audio steganography may alter inaudible frequency components, and document steganography can exploit formatting or whitespace, so the detection method and tool an examiner applies depends on correctly identifying which carrier format is in play.
Related terms
- DCT Coefficient Embedding
- A steganographic technique that hides data in the quantised discrete cosine transform coefficients of a JPEG image after compression. Because the embedding...
- LSB Substitution
- Least-significant-bit substitution: the lowest-order bit of each sample value (pixel colour channel or audio sample) is overwritten with one bit of the...
- Spread-Spectrum Embedding
- A technique that distributes the energy of the hidden message across many frequency components at very low amplitude, similar to a wideband...
- Steganalysis
- The forensic discipline of detecting the presence of hidden data in a carrier file. Steganalysis uses statistical tests (chi-squared, RS analysis, sample...
- Stego Object
- The modified carrier file containing the embedded secret data. A stego object should be visually or audibly indistinguishable from the cover medium,...