Code

Where privacy for recorded material or for transmitted messages or information is required, as for example for military, diplomatic, commercial or political usage or for personal reasons, a system of image or symbol displacement may be used. The original symbols, mainly the alphabetic characters or phonetics of a text, with some numerics, and the original pictorial images (diagrams, maps, photographs, drawings) may be transposed, or they may be removed and substituted for (encoded), or they may be mechanically, electrically or electronically masked, altered or distorted. In a wide sense, coding is synonymous with information concealment and therefore includes non-cryptographic techniques such as microform copying of documents, high-speed voice transmission, ultra-violet light sensitive inks and conversion of data to electromagnetic digital memories. In commercial advertising and political propaganda coding technologies may be used to carry subliminal messages.