Code
In classical cryptography, a code replaces meaningful words or phrases with assigned symbols or groups, usually through a codebook.
Definition
In its historical cryptographic sense, a code substitutes whole meaningful units—words, phrases, names, or instructions—with code groups listed in a codebook. A recipient reverses the substitution using the same book. Nomenclators combined a codebook with ciphered letters or numbers.
Code versus cipher
A cipher transforms smaller elements such as letters, symbols, or bits by an algorithm controlled by a key. A code depends on a vocabulary of assigned meanings. Capturing a codebook may expose every entry, while breaking one cipher key need not reveal messages protected with different keys.
Modern uses of the word
The word code is also used for Morse code, character encodings, error-correcting codes, source code, and access codes. These meanings are distinct. Morse, A1Z26, and Base64 provide a public representation and should not be treated as encryption.
No. Its symbol mapping is public and provides no secret; anyone who knows Morse can read it.
A code maps meaningful units through a codebook, while a cipher applies a keyed algorithm to smaller data elements.
A secret codebook can conceal messages temporarily, but distribution and capture are serious weaknesses. Modern cryptography relies on analyzed algorithms and manageable keys instead.