Code
A code was a system to convert a piece of information into another form. Codes were most often used to send messages or define situations. Codes could be decrypted using a code key. ()

An early code that was used for communication on Earth during the 19th century was Morse code. (; )

The intersat code was used in the 21st century for inter-stellar communications. ()

Early computer systems on Earth were based on binary code, and later Federation systems could even support trinary code. ()

Codes were often used to encrypt information, including the Federation's Code 2 and Code 3 in the 23rd century; the former had been broken by the Romulans by stardate 3478.2, and thus was replaced by the latter. ()

Many other codes were simply used to transmit information quickly, including Code One alert to indicate a declaration of war or disaster, () Code 710 to indicate planetary quarantine, () Code 1-Alpha-Zero for a ship in distress, () Code Factor 1 for a possible invasion of the Federation, () code blue, or blue alert, used to indicate a change in starship flight status, () code white resuscitation to indicate the need to resuscitate a dead individual, () Emergency Code 1 for intruder alert, () and Transporter Code 14 to destroy an object in a transporter beam. ()

Codes could also be used to designate messages for specific individuals, such as code 47 meaning "for captain's eyes only." ()

Critical ship systems required pass-phrase access in the form of prefix codes (; ) and authorization codes. (; ; )

In 2151, the Vulcans sent encrypted coded secret messages to . It was decrypted by communications officer Hoshi Sato and identified as private Vulcan letters sent to T'Pol. ()

In August of 2151,  first officer Matthew Ryan interrogated and tortured a Nausicaan prisoner to get the codes for the shield frequencies of his ship. ()

See also 
 Decoding
 Starfleet ID code

External link 
 
Communications technology
Security