This document describes the QDLPlgXTEA class of the QDLPluginEncryptionPS plugin for Xojo/RealStudio.This class implements the Data Encryption Standard (DES) block cipher.

DES is a previously predominant symmetric–key algorithm using blocks of 64–bits for the encryption of electronic data. It was highly influential in the advancement of modern cryptography in the academic world. Developed in the early 1970s at IBM and based on an earlier design by Horst Feistel, the algorithm was submitted to the National Bureau of Standards (NBS) following the agency's invitation to propose a candidate for the protection of sensitive, unclassified electronic government data. In 1976, after consultation with the National Security Agency (NSA), the NBS eventually selected a slightly modified version, which was published as an official Federal Information Processing Standard (FIPS) for the United States in 1977. The publication of an NSA–approved encryption standard simultaneously resulted in its quick international adoption and widespread academic scrutiny. Controversies arose out of classified design elements, a relatively short key length of the symmetric–key block cipher design, and the involvement of the NSA, nourishing suspicions about a backdoor. The intense academic scrutiny the algorithm received over time led to the modern understanding of block ciphers and their cryptanalysis. DES is now considered to be insecure for many applications. This is chiefly due to the 56–bit being too small. There are also some analytical results which demonstrate theoretical weaknesses in the cipher, although they are infeasible to mount in practice. The algorithm is believed to be practically secure in the form of , although there are theoretical attacks. In recent years, the cipher has been superseded by the . Furthermore, DES has been withdrawn as a standard by the National Institute of Standards and Technology (formerly the National Bureau of Standards) (src. Wikipedia).

The QDLPlgDES class can use a 56–bit fixed length .

The QDLPlgDES class constructors are called when you create a new instance of the class, while the ˜QDLPlgDES class destructor, is called automatically when the class is no more in use. Also, you can invoke the class destructor by setting the instance of the class to nil.

The QDLPlgDES class implements the following initializers: