/ˌstɛɡəˈnɒɡrəfi/
noun — "hidden communication within digital media."
Steganography is the practice of concealing information within another medium so that the presence of the hidden message is not detectable to casual observers. Unlike cryptography, which focuses on making data unreadable to unauthorized parties, steganography emphasizes secrecy by embedding information in a way that appears innocuous or ordinary. Common digital mediums include images, audio files, video streams, and text documents.
Technically, digital steganography works by manipulating redundant or less noticeable elements in the carrier file. For example, in images, the least significant bits (LSBs) of pixel values can encode hidden data without perceptibly altering the image. In audio, inaudible frequency bands or phase shifts may carry information. In text, spacing, font variations, or invisible characters can encode messages. The size of the hidden payload and the choice of embedding algorithm affect detectability and robustness. Techniques range from simple LSB insertion to advanced methods using error correction, encryption, and spread spectrum encoding.
Operationally, sending a steganographic message involves selecting a carrier file, applying an embedding algorithm to hide the payload, and transmitting the carrier over a standard channel. The recipient, knowing the method and keys if applicable, extracts the hidden data. Tools like Steghide or OpenPuff automate embedding and extraction in images and audio. For example:
steghide embed -cf image.jpg -ef secret.txt -p password
steghide extract -sf image.jpg -p password
This sequence hides secret.txt inside image.jpg using a password and later retrieves it without altering the image's visible content.
In practice, steganography is used for confidential communication, watermarking digital media, embedding metadata, and digital rights management. Security applications may combine cryptography with steganography to protect sensitive information further. Detection of steganography, called steganalysis, involves statistical analysis of carrier files to identify anomalies caused by embedded data.
Conceptually, steganography is like writing a secret note in invisible ink on a postcard: the postcard itself appears normal, but those with the correct method can reveal the hidden message, ensuring covert communication.
See Cryptography, Steganalysis, Digital Watermarking, LSB, Encryption.