Encryption And Decryption A Type Of Cryptography Computer Science Essay

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In this chapter, an introduction to Encryption and Decryption, a type of cryptography is firstly presented. This chapter also briefly discusses the analysis of Encryption and Decryption and the computer based measurement system.The problem definition and the thesis objectives are also highlighted.Finally, the chapter end with the chapter organization.

1.1 An introduction to Encryption and Decryption, a type of cryptography

Encryption and Decryption, a type of cryptography, refers to the process of scrambling information so that the observer cannot be detect the data.

In mathematics, computer science, and related subjects, an 'algorithm' is an effective method for solving a problem expressed as a finite sequence of instructions. Algorithms are used for calculation, data processing, and many other fields. Each algorithm is a list of well-defined instructions for completing a task. Starting from an initial state, the instructions describe a computation that proceeds through a well-defined series of successive states, eventually terminating in a final ending state. The transition from one state to the next is not necessarily

deterministic. Some algorithms, known as randomized algorithms, incorporate randomness[1].

The proposed projects is to create the algorithms where it is use to convert of information, rearranging the original massage produce output referred as ciphertext.

Similarly a cryptographic key is a piece of data used to encrypt or decrypt to plaintext. The Crypto,from the word cryptographic mean is it has its origins in the Greek word KRUOTOS, which means hidden. Thus the objective of cryptography is to hide information so that only the intended recipient can read it.[2]

Figure 1.1 is example of the Simple block diagram for Encryption and Decryption and also show about the Lucifer algorithm invented, encryption and decryption uses a single 64-bit key consisting 56 bit of data and 8 bits of parityâ€"and operates on data in 64-bit [3] .

64 bit output

56 bit data + 8 bit parity

Encryption and Decryption

56 bit key

Figure 1.1: Simple block diagram for Encryption and Decryption

1.2 Problem Statement

At present there are many encryption and decryption, especially in the communication system provided in a variety of application.

Encryption and decryption is particularly impacted in the field of military communications and reliable security data to protection for transmitting.

This ciphertext is used in the military is to send information such as direction, strategy, secret codes and other information that can not be know by the national foe during the war.[4]

Creating this system is the process by which information can not be detect by the national foe. The information can not be recognizing by the national foe because this system is using encryption data and decryption data. [4]


This project are to create a system that can protect electronic data (secret information) which Consist of encryption and decryption process and to fully design an encryption and decryption algorithm using VHDL. The objectives of this project are

To understand how the Encryption and Decryption process.

To fully design an Encryption algorithm and Decryption algorithm using VHDL.

To make use Quartus II software as a design and synthesis tool.

1.4 Chapter Organization

Chapter 1: This chapter starts with an Introduction which highlights the problems under investigation by describing the status of problem conceptually and theoretically. It contains the introduction of the thesis, problem statement and scope of study, objective of the project, project expectations and the chapter organization.

Chapter 2: This chapter is a Literature Review that compiles the studies done by others based on the title of the project. Under the literature review, this chapter discussed on the features need to be include in designing the system.

Chapter 3:. The methodology chapter describes the steps that has been taken while doing the project from the beginning until the end. The main content of the chapter are the flow charts and the description of each step of the process.

Chapter 4: This chapter presents the result of the algorithm and discussion observed. The results obtained are presented as a series of figures, tables, with textual description and discussion. The analysis outcome of the research is also discussed in relation to the evidences obtained from project work and theories reported in Literature Review .

Chapter 5: The chapter is the Conclusion of the thesis and which signalized the whole project a done



2.0. Overview

Target key in this chapter is to introduce the host range of background information and research done be me, most methods have been widely used than the-experts and researchers to determine how the process of encryption and decryption using verilog, C++ and cadence. Theoretical method is presented using the VHDL.

Literature review is part of the thesis is presented in this chapter. The parts covered are show as below:

Symmetric cryptography

Advantages Public-Key Cryptography

Disadvantages of Public-Key Cryptography



Operations of Encryption and Decryption

Data Encryption Standard Algorithm

VHDL (VHSIC Hardware Description Language)

2.1. Symmetric cryptography

Symmetric cryptography is the result of classical cryptography. All classical cryptosystem is a system secret key. Most of them can be seen as a block cipher, if not, the stream cipher. Symmetric algorithms are currently still secret-key system and the block or stream cipher. However, because of the technical and cryptographic kriptoanalisis has developed significantly. Symmetric cipher because it is the fastest and most widely used cryptographic algorithms.They can provide privacy, authentication and integrity services, if implemented properly.

Block cipher sharing a message of fixed size blocks and encrypt each one by one. This function can not be used until a full block of data available. Stream cipher does not work on fixed size blocks. Each amount of data can be automatically encrypted. Encryption is done by the main stream, often independent data. The plaintext and the keystream and then combined in a mixing function. Mixing function is usually very simple, stream cipher using XOR most. Since the keystream can be precomputed before the data arrived, the stream cipher can be faster than block cipher in some cases

. Basic objective of the Symmetric cryptosystem is to use the button to change the plaintext to make it read / known. This technique is called the policy confusion and diffusion. About this match substitution and permutation. A strong cipher should contain two operations. ClaudeShannon,who developed the concept, used round alternately substitution and permutation,and this design has been copied in many ciphers.Cryptography further divided into two pqrts,the first is Public-button and the second is the Symmetric cryptography.[5]

Public key cryptography is a method of secret communication between two parties without the need for early exchange of secret keys. It could also be used to create digital signatures. Public key cryptography is the delivery of basic and widely used technology worldwide, and provides information on the internet.

It is also known as asymmetric key cryptography because the key used to encrypt a message different from the button is used to decrypt. In public key cryptography, the user has a cryptographic key pair of public key and a private key. Private key secret while the public key can be distributed widely. Messages are encrypted with the recipient public key and can only be decrypted with the private key is necessary.Mathematics-

related buttons, but the private key can not feasibly (that is in actual practice) derived from the public key.[6]

Advantages of Public-Key Cryptography

The main profit of public key cryptography is increased security and convenience; private keys need not be transmitted or revealed to anyone.In secret-key system, otherwise, the secret button to be sent (either manually or through the channels of communication), and maybe there is a possibility that an adversary can find the secret key for their delivery

Other major profit from the public key is that they can provide a method for digital signatures. Authentication via secret-key system requires a shared secret and sometimes requires trust of a third party can. As a result, the sender can reject previous message confirmed by claiming that the secret together, somehow compromised by one of the shared secret

For example, Kerberos authentication system involves a button-secret data center that stores copies of all user secret key, an attack on the database will enable the falsification of the area. Public key authentication, on the other hand, the prevention of

rejection, each user has a responsibility to protect its private key.It's the public key authentication is often referred to as non- repudiation.[7]

2.3 Disadvantages of Public-Key Cryptography

A disadvantage of use of public key cryptography for encryption is speed: there is a secret key encryption methods are popular in significantly faster than existing methods of encryption that is currently public key

However, public key cryptography can be used with secret-key cryptography to get the best of both worlds. For encryption, the best solution is to combine public and secret key systems, to gain better security of public-key system and gain speed system secret key.

Public key system can be used to encrypt a secret key used to encrypt files public key cryptography may be vulnerable to the impersonation; however, even if the user's private key 'is not available. A successful attack on the certification will allow the enemy to an enemy who chooses to imitate, using the public key certificate of the compromised key to bind the enemy to choose another username


In some situations, public key cryptography is not necessary and secret-key cryptography enough. These include the environment in which the secret agreement, the button can occur, for example, the user conference in private. This also includes the environment in which a single authority knows and manages all the keys, for example, private banking system.

Since the power to know all the keys are no more profits for some to become "public" and other "private." In addition, public key cryptography is usually not required in single-user environment. For example, if you want to save your personal files encrypted, you can do with the secret-key encryption algorithm used, for example, your personal password as the secret key. In general, public key cryptography is suitable for multi-user environment is open.

Public key cryptography is not intended to replace the secret key cryptography, but to complement it, to make it more secure. The first use of public key techniques is to change the key in a specified secret-key system is still one of its primary functions. Secret-key cryptography and is still very important subject of extensive ongoing research and study. A number of secret-key algorithm debated in parts of the block cipher and stream cipher[8]

2.4 Encryption

Encryption is a form of cryptography that "disorderly" is the plaintext to ciphertext.Encryption understand basic security measures such as digital signatures, digital certificates and Public Key Infrastructure using this technology to make transactions over the computer

Using computer-based encryption techniques to encrypt and decrypt key data. Is a key variable (sometimes represented as a password) which is a binary number of the larger. Length is measured in bit key and bit more balance, balance is more difficult to "Crack".

The key is just one component in the encryption process. This should be used in conjunction with the encryption algorithm to generate the method is usually categorized as good ciphertext.Encryption Symmetric, depending on the number of keywords used.[9]

2.5 Decryption

Decryption is the opposite, in other words, moving from the ciphertext back into plaintext understood. Cipher is a pair that created the encryption algorithm and decryption reversing.

Detailed operational cipher is controlled both by the algorithm and in each case the key. This is a secret parameter (ideally known only by the settlement) for a special message exchange context

Important button, the password without the key variable may be damaged with only trivial knowledge of the password used and therefore not useful (or even counter-productive) for most purposes

Historically, cipher used directly for encryption or decryption without additional procedures such as authentication or integrity checks.The most widely used type of encryption is encryption simetris, the aptly named because the use of a single button for both encryption and decryption process. Encryption is often referred to as secret key encryption and secret sharing [10].

2.6 Operations of Encryption and Decryption

An encryption scheme consists of three algorithms:

A key generation algorithm. For a symmetric key, this is often an algorithm that simply picks a random key of a certain length and people often forget to mention it when talking about symmetric encryption schemes. Asymmetric key generation algorithms are typically more mathematical and produce more complicated keys.

An encryption algorithm. This takes as input a message (or plaintext) and some kind of key, and outputs a ciphertext.

A decryption algorithm. This takes as input a ciphertext and some kind of key, and outputs a message

The operations of encryption start with a message that has to be sent securely. This could be text, numeric Data or Secret Codes

2.3 Data Encryption and Decryption Standard Algorithm

This system works by encrypting groups of 64 message bits, which is the same as 16 hexadecimal numbers. To do the encryption, this system uses "keys" where are also apparently 16 hexadecimal numbers long, or apparently 64 bits long. However, every 8th key bit is ignored in the this algorithm, so that the effective key size is 56 bits. But, in any case, 64 bits (16 hexadecimal digits) is the round number upon which Encryption and Decryption is organized.

For example, if we take the plaintext message is "2872762F771B15E8", and encrypt it with the key "1234567890987654", the ciphertext produced "0000000000000000". If the ciphertext is decrypted with the same secret key "1234567890987654", the result is the original plaintext "2872762F771B15E8".

2.4 VHDL (VHSIC Hardware Description Language)

In order to complete the design, the VHDL is one of the most important tools used. Device description language VHDL is a great acronym stands for the very high speed integrated circuit Hardware Description language. It was originally developed on the

orders of the Department of Defense. They need a more efficient way to document the behavior of the ASIC design service companies were present.[ represented 11,12]

It was developed as an alternative, the manual is a complex of norms. The idea to simulate such evidence would be an interesting prospect and logic simulator developed can download the VHDL description as entered. From here the synthesis of the hardware level to focus the study. Currently, the country-art synthesis tools can create the device's hard for a large subset of VHDL language and synthesized at least be supporting a subset of the IEEE1076.6-1999. Syntax of VHDL is derived from there, the building is added to address emerging paralelisme in hardware design. The language is strongly typed and case insensitive[13,14]

Worst version that is served in the IEEE 1076-1987 standard is limited and the new version appeared in 1993 in the IEEE, the standard language from 1079 to 1993 the increase consistency. There are various standards of review and update the language since, but the 1993 version is the most prominent and widely used. Both language versions of neglecting the needs of multi-value logic that comes standard IEEE 1164.[15]

This standard defines the type of logic called respectable ninth-std logic. It has become a standard for the type used for multi-logic vote in the VHDL description. This language has been extended in a series of libraries. One of these libraries are libraries that

implement the numerical std signed and unsigned type. Type of geometry allows for the size of arbitrary logic vector. [16]

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Standard for VHDL Register Transfer Level (RTL) synthesis, 1999.

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