Hiding Information

Steganography Concepts

Steganography: Hiding the existence of a message within a cover object so that an observer does not realize hidden data is present.
Cover Object: The carrier medium (image, audio, video, text) used to hide a secret message.
Payload: The hidden message embedded within a cover object.
Null Cipher: A technique that hides messages within ordinary text using predefined patterns, such as taking specific letters after punctuation or the nth letter of each word.
Concealment Cipher: Same as Null Cipher
Microdot: A photograph shrunk to the size of a period, used to hide messages in documents or images.
Chaffing and Winnowing: A technique that pairs real messages with irrelevant data, each accompanied by a MAC, achieving confidentiality without encryption.
Steganalysis: The practice of detecting hidden content in files.

LSB Steganography (Least Significant Bit): A technique that replaces the least significant bits of pixel color values with message bits, producing changes imperceptible to humans.
Frequency Domain Steganography: Embedding data in high-frequency areas of images (noisy regions) where humans do not notice changes.
Audio Steganography: Hiding data in audio files using techniques such as LSB encoding, echo hiding, phase coding, or spread spectrum methods.
Echo Hiding: An audio steganography technique that adds imperceptible echoes to encode hidden data.
Network Steganography: Hiding data in network communication through packet headers, timing intervals, TCP sequence numbers, or DNS queries.

Watermarking: Embedding identifying information into content so it persists even if someone tries to remove it.
Fingerprinting: A variant of watermarking that embeds unique identifying information into each distributed copy to trace leaked copies to specific recipients.
Fragile Watermark: A watermark designed to break if content is modified, used for authentication and tamper detection.
Robust Watermark: A watermark designed to survive transformations such as cropping, compression, and resampling.
Printer Tracking Dots: Nearly invisible yellow dots embedded by color laser printers that encode the printer's serial number and timestamp.

Private Browsing Mode: A browser mode that does not send cookies, does not save history, and discards cached pages at session end, but does not hide your IP address from servers or ISPs.
Surface Web: Content indexed by search engines.
Deep Web: Unindexed content such as database query results and private pages.
Dark Web: Intentionally hidden content requiring special software like Tor to access.
.onion Address: A special-use domain for Tor hidden services, derived from hashed public keys.

Onion Routing: A technique where messages are encrypted in multiple layers, with each relay stripping one layer before forwarding.
Tor Relay: A volunteer-operated server that forwards encrypted traffic for the Tor network.
Tor Consensus Document: A signed document describing all valid Tor relays, their IP addresses, ports, bandwidth, and public keys, updated hourly.
Circuit: A path through three Tor relays (entry, middle, exit) used for anonymous communication.
Entry Relay (Guard): The first relay in a Tor circuit that knows the user's IP address but not the destination.
Middle Relay: The second relay in a Tor circuit that knows neither the user nor the destination.
Exit Relay: The final relay in a Tor circuit that contacts the destination but does not know the user's IP address.
Correlation Attack: An attack where an adversary observing both entry and exit traffic correlates timing and message sizes to link users to destinations.
Sybil Attack: An attack where an adversary runs many relays to increase the chance of controlling both entry and exit nodes of a circuit.
Tor Bridge: An unlisted Tor relay using obfuscated protocols (such as obfs4) to help users bypass censorship.

Garlic Routing: A technique that bundles multiple messages together at each relay to make traffic analysis harder.
I2P (Invisible Internet Project): An anonymous network using garlic routing and unidirectional tunnels, focused on hosting hidden services.