Code

This article is about code as transmission rules, for other meanings see code (disambiguation). Coding is a redirect to this article, for the mechanical coding of electrical connectors see Coding (connector).

A code (German pronunciation [koːt] or [kɔʊ̯d]) is a mapping rule that uniquely assigns to each character of a character set (original image set) a character or character sequence from a possibly different character set (image set). For example, Morse code establishes a relationship between letters and a sequence of short and long audio signals and pauses (and vice versa).

In communication science, a code in the broadest sense refers to a language. All communication is based on the exchange of information that is generated by the sender according to a certain code and interpreted (decoded) by the receiver according to the same code.

For example, electronically transmitted or stored data consists of a long series of zeros and ones (bits) whose combination is defined as digits, characters and/or letters (e.g. 11000001 = 'A'). In another code, the same combination of bits could mean, for example, the number 193. For other types of data, e.g. measured values or the nucleic bases in DNA strands, codes also specify which manifestations mean what.

In coding theory, the elements that make up a code are called "codewords", and the symbols that make up the codewords form an "alphabet".

General meaning

In general, a code is an agreement on a set (a quantity) of characters such as indexes, icons, or even symbols (meaning carriers, or references) for the purpose of exchanging information. Information does not exist in "pure" form; it is always formulated in some way. In general terms, a code is a formulation of information in which the characters are subject to syntactic, semantic, and pragmatic rules. This implies the following elements:

at least one information-formulating instance (recorder/transmitter)
at least one information-receiving instance (reader/receiver) - can also be identical with (1) in exceptions
a concrete or abstract content to be transmitted, the information
an agreement for the purpose of information formulation and, where appropriate, information transmission. This contains a set of meaning carriers or symbols known to both entities (1. and 2.) and, if applicable, rules for the use of the symbols

Human language, animal sounds, but also the semiochemical molecules in bacterial communication and plant communication (auxin) are codes of different complexity and capacity. In the case of animal sounds, bacterial, fungal and plant communication, the "agreement" has arisen through natural evolution.

Definition

A code over the alphabets and is an injective mapping (= encoding)

$c\colon A\rightarrow B^{{+}}$ ,

which assigns non-empty words to symbols of the alphabet over the alphabet The elements of the image set c(A) are called code words of the code. An extension of a code is called the mapping $c^{{\ast }}\colon A^{{+}}\to B^{{+}}$ defined by.

$c^{{\ast }}(a_{1}\ldots a_{n})=c(a_{1})\ldots c(a_{n})$ ,

where $a_{1}\ldots a_{n}$ is a word over the alphabet . A code is called immediately decipherable if no codeword occurs with it as the initial segment of another codeword. It is called uniquely decipherable if its extension $c^{{\ast }}$ is injective. Every immediately decipherable code is also uniquely decipherable, but there are also uniquely decipherable codes that are not immediately decipherable.

Questions and Answers

Q: What is a code?

A: A code is a way of changing information into something else, such as a word, number or symbol used to represent a word, phrase or syllable in plaintext. It is one of the earliest forms of cryptography.

Q: How does encryption work?

A: Encryption or cryptography works by changing letters into 1's and 0's. This method was invented for punched tape and now the usual alphanumeric code is ASCII. It can also be done using Morse Code which changes letters to dots and dashes.

Q: What is cryptanalysis?

A: Cryptanalysis is the process of breaking down codes to understand how they work so that messages written in that code can be understood. Nations and other organizations have been breaking each other's ciphers for many centuries.

Q: What are encryption algorithms?

A: An encryption algorithm is an algorithm (code) used to make a message secret. To change a secret message back, a decryption algorithm must be used.

Q: What are some examples of codes being used?

A: Codes are often used as a way of keeping messages secret through encryption or cryptography, but they can also be used as an easier way of sending messages - for example when people on two different boats want to send a message they may use flag codes or Morse Code instead of shouting across the water. Some people even write codes as games - making ciphers and then trying to break them!

Q: Is there any difference between codes and cyphers?

A: Yes, there is a difference between codes and cyphers - while both involve changing letters into something else, with codes it involves representing words with symbols whereas with cyphers individual letters are encrypted (changed).