Darbe apžvelgiami esami duomenų šifravimo metodai, jų klasifikacija. Taip pat detaliai aprašomi keletas šifravimo algoritmų. Pagal AES šifravimo algoritmą sukuriama informacijos kodavimo programa Visual Basic kalba ir pademonstruojama keletas palyginamųjų rezultatų su jau egzistuojančiomis, analogiškomis programomis. / Data protection problem is relevant in now days living. This paper takes a review of the existing methods and programs in digital data cryptography. Also it explains AES (advanced encryption standard) method, the most trustful one and overviews software tool, that was coded and used in experiments analysing this algorithm. The new AES class, that was created in this project, is compared using few parameters with the older one, created by Microsoft. Despite the only purpose, to create a better program, the older implemented AES cipher class and it’s methods beats the new one.

Šiame darbe supažindinama su kriptografija, jos istorija, pagrindiniais kriptografijos principais, šifravimo algoritmų tipais, jų taikymo sritimis, privalumais bei trūkumais. Taip pat apibrėžiamos pagrindinės sąvokos ir terminai, išvardinti kriptoanalitinių atakų tipai ir reikalavimai kriptosistemoms. Svarstoma, ar egzistuoja absoliučiai patikimi šifravimo algoritmai. Trumpai aprašomi pagrindiniai šifravimo būdai ir kriptoanalitiniai metodai. Darbe yra nagrinėjami blokiniai (DES, GOST, LOKI 91, SAFER K-64, FEAL–8, Blowfish, AES (Rijndael)) šifravimo algoritmai, išaiškinama jų svarba kriptografijoje, išsamiai aprašoma jų struktūra, atsparumas kriptoanalizei, išaiškinami privalumai bei trūkumai. Nagrinėjami algoritmų taikymų ypatumai, galimybės, apribojimai. Analizuojami algoritm��� atsparumo kriptoanalizei kriterijai, jų svarba bei algoritmų patikimumo priežastys. Išnagrinėjus esamus blokinius šifravimo algoritmus, buvo atliktas jų tarpusavio palyginimas. Nustatyta, kad šifravimo algoritmo patikimumas priklauso nuo atsparumo kriptoanalitiniams metodams, rakto ilgio, algoritmo architektūros. Išaiškinami pagrindiniai algoritmų privalumai: realizavimo lankstumas, kintamas rakto ilgis, numatantis algoritmo ilgaamžiškumą. Taip pat nurodoma, kad duomenų sauga priklauso ne tik nuo šifravimo algoritmo, bet ir nuo kitų informacijos saugos aspektų: raktų apsaugos, jų paskirstymo, atsitiktinių skaičių generavimo būdų. / This work presents cryptography, its history, main principles of cryptography, types of ciphers, their application range, advantages and disadvantages. Key concepts and term are also defined. Complexity of attacks and requirement to cryptographic systems are listed and described. A question of the existence of the absolutely safe ciphers is considered. The main encryption modes and cryptanalysis methods are described. Research of the most prominent block ciphers and their importance to many cryptographic systems is presented in this work. The structure of block ciphers, their resistance to cryptanalysis are given in details and expositive strength of block ciphers. Their advantages and disadvantages are discovered and stated. Ciphers application range, their potential and restrictions are researched. Criteria of the resistance of ciphers to cryptanalysis, their importance and the reasons of cipher reliability are analyzed. After analyzing the block ciphers such us: DES, GOST, LOKI 91, SAFER K-64, FEAL–8, Blowfish, AES (Rijndael), their inter comparison was performed. It was noted that the reliability of ciphers depends on their resistance to cryptanalysis methods, key length and their architecture. The following major advantages of ciphers as flexibility of realization, changeable key length and facilitating cipher durability are discovered. The following conclusion has been drawn, that data safety depends not only on ciphers, but also on other aspects of information safety... [to full text]

The aim of the final Master degree work is to create a method, algorithms and program for cryptographic security of text files. The algorithms of cryptographic security and algorithms aspects are analyzed in the work. Construct program is used for coding / decoding text files using Pseudo – Random Number Generator and it is applied to use in Windows operating system. The program and instructions for its user are formed. The experimental adaption of method and program is done. The program synthesis of coding / decoding text files is described.