Communication Protocol Overview


Message exchange
Requests and responses are hidden in visible HTTP traffic
Requires a hiding function
Messages exchanged as a stream of symbols

Symbol construction 
How symbols map to message fragments
A group of symbols is called an alphabet
Upstream: set of URLs on a responder's Web site
Downstream: high-frequency components in images

Modulation 
Specifies a particular function for symbol construction
Maps a sequence of visible HTTP requests to a hidden message