Encryption
Encryption was a method of coding information in a way intended to make it unreadable to anyone but the intended recipients.

Several species used encryption to protect their data and the access to it. The way encryption codes were created differ; some codes were easy to break or to circumvent and other codes were difficult or even impossible to break. The Qomar, a Delta Quadrant species, thought at first that Earth music was a form of encryption. ()

Encryption was not only used to protect data, such as personal files, but also for communication protocols. The ops protocol on Deep Space 9 was protected by an encryption system. ()

In Earth's 20th century, some databases were also protected by encryption codes. A 24th century Starfleet tricorder had no problem with breaking such a code. ()

As encryption codes differ in complexity – a fractal-based encryption code could lock out the main computer of a Sovereign-class starship in such a way that even the Borg had trouble bypassing it – encrypting or decrypting such codes might take some time. () 

In the 24th century, encryption programs were used to bypass access protocols. () 

Although an encryption sequence could be broken by a computer a person could also connect themselves directly to a terminal by means of a dataport and so try to break the encryption. ()

Known implementations

Aquatic 
Xindi-Aquatic encryption protocols consisted of at least one encryption layer. ()

Klingon 
A 22nd century Klingon encryption protocol had encryption layers which extended to the quantum level. ()

Cardassian 
Elim Garak once said he invented the basic encryption codes for the Obsidian Order. () 

Most 24th century Cardassian encryption codes used a recursive encryption algorithm. () When created on some computer systems (such as the one on Deep Space 9), an encryption could only contain seven sequences. ()

Cardassian Prefects tended to encrypt their files. ()

Romulan 
Romulans used a progressive encryption lock. This lock consisted of a 43-part cipher key and was used in their encryption entry sequence. Data could not break the 29th level of such an encryption code while Spock could. ()

Komar 
The Komar used at least six levels of encryption to prevent access to 's holo-emitters in the hope of preventing the reactivation of The Doctor. ()

The Hierarchy 
The Hierarchy could not break Voyagers encryption sequences used for their security protocol, and compromised The Doctor's holographic program instead. ()

Borg 
The Borg had their own encryption codes, by which they even could block Starfleet commands. () Encryption code 294 was used to perform such a block. ()

Starfleet 
24th century Starfleet codes were made up of encryption algorithms. () Every encryption key had an implementation date, the time and date it was to be used. One encryption key on Voyager had a stardate of 48423, one month after they had left Deep Space 9. ()

Starfleet also had emergency encryption codes. These were used for short messages in case of emergency. ()

An encryption circuit contained hardwired security codes. The processing of encryptions was done by encryption subprocessors. 24 isolinear chips with the number 58966/D made up the asymmetric encryption circuits of a  starship. ()

Starfleet encryptions even had a frequency. ()

Vulcan 
In 2151,  discovered encrypted messages from the Vulcan combat cruiser Ti'Mur while working in engineering. He asked communications officer Hoshi Sato to decrypt the messages only to find personal letters adressed to T'Pol. ()

Hoshi Sato remarked that breaking a Vulcan encryption code would be easier than finding out what Malcolm Reed's favorite food was. ()

See also 
 Classified information

External link 
 
Communications technology
Security