# Cryptography and network security solved problems pdf writer

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Scilab numbering policy used in this document and the relation to the above book. Exa Example Solved example.

## Mobile security

Average entropy per byte of encryption. Average number of bits demanded to optimally encode a byte of encrypted data. Facebook Twitter Linkedin Flickr youtube. Research Article Open Access. DOI: Encryption is the process of encoding information or data in order to prevent unauthorized access. These days we need to secure the information that is stored in our computer or is transmitted via internet against attacks. There are different types of cryptographic methods that can be used.

Basically, the selecting cryptographic method depends on the application demands such as the response time, bandwidth, confidentiality and integrity. However, each of cryptographic algorithms has its own weak and strong points. Also, we will show the comparisons between the previous cryptographic techniques in terms of performances, weaknesses and strengths.

In recent years, many applications based on internet are developed such as on-line shopping, internet banking and electronic bill payment etc.

Such transactions, over wire or wireless public networks demand end-to-end secure connections, should be private, to ensure data authentication, accountability and privacy, integrity and availability, also known as CIA triad [25]. For this reason, the proposed algorithm has utilized Feistel Cipher in safe wifi design sWiFi.

Encryption is one of the principal means to guarantee security of sensitive information. Encryption algorithm performs various substitutions and transformations on the plaintext original message before encryption and transforms it into ciphertext scrambled message after encryption. Many encryption algorithms are widely available and used in information security. Encryption algorithms are classified into two groups: Symmetrickey also called secret-key and Asymmetric-key called publickey encryption [2].

A secure Wi-Fi system for wireless networks: experimental evaluation is a network security system for an application using the proposed algorithm. From the key exchange, it depends on the key used to encrypt data sent over an unsecured Internet channel.

A secure data transmission feature of CC cloud computing has plays a very important role in business perspective. For utilizing cloud computing, business trends have to play a lot of money to the cloud service provider. Cloud service provider also has guaranteed either the confidentiality or integrity of the data. This paper proposes an intensive study for the idea of sending already encrypted file through cloud in spite of the original file using RSA and DES algorithm of cryptography [4].

The aim is to provide evidence of which of the encryption methods has more powerful and effectiveness technique when encrypted file is transmitted, so original file is not available even at the network. So even if any intermediate user sees the data, he will not be able to understand the data.

Hence, security of cloud data will be increased. This work can be enhanced using hybrid approach by integrating multiple cryptography algorithms [28]. In this paper, the analysis has been done based on the following metrics: [1]. Encryption time depends upon key size, plaintext block size and mode. In our experiment, we have measured encryption time in milliseconds. Encryption time affects performance of the system [3].

Encryption time must be less making the system fast and responsive. The decryption time is desired to be less similar to encryption time to make system responsive and fast.

Decryption time affects performance of system. In our experiment, we have measured decryption time is milliseconds. This memory requirement depends on the number of operations to be done by the algorithm, key size used, initialization vectors used and type of operations.

The memory used impacts cost of the system. It is desirable that the memory required should be as small as possible.

If there is a small change in an input, the output changes significantly. This is also called avalanche effect. We have measured Avalanche effect using hamming distance. Hamming distance in information theory is measure of dissimilarity. We find hamming distance as sum of bit-by-bit xor considering ASCII value, as it becomes easy to implement programmatically. A high degree of diffusion i. Avalanche effect reflects performance of cryptographic algorithm.

A lack of entropy can have a negative impact on performance and security. Since, the encrypted bit will be transmitted over a network after encoding; this metric tells us the bandwidth required for transmission. If an encrypted bit is encoded with fewer bits, it will consume lesser bandwidth and lesser storage as well. Hence, this impacts cost. As we have mentioned that Encryption is the process of encoding information or data in order to prevent unauthorized access.

Each one of them serving different topology and all provide secure transmitted data through network links and ensure authentication and confidentiality. All these end to end encryption and decryption algorithms have to be applied in the physical layer and security layer of the computer application. At the same time a specific IP configurations are need to be considered as well as the protocol that will be used to transmit the traffics.

The diagram below showing us the cipher security classes which are subdivided into 2 models: classical and modern class. The most common and used is the modern class due to the dynamic and static cryptography techniques that this technique was deployed with.

It is known also by its types; i. Secret Key Symmetric Key in a symmetric cryptosystem, the same key is used for encryption and decryption [5,11]. Public Key Asymmetric Key in an asymmetric, the encryption and decryption keys are different but related. The encryption key is known as the public key and the decryption key is known as the private key. The public and private keys are known as a key pair [5]. So, our focus point in this paper is on these two types with their classes to show the significance for each one of them through our literature and to prove which one is the best with what environment.

Figure 1. AES algorithm can support any combination of data bits and key length of , , and bits. During encryption decryption process, AES system goes through 10 rounds for Ibit keys, 12 rounds for Ibit keys, and 14 rounds for bit keys in order to deliver final cipher-text or to retrieve the original plain-text AES allows a bit data length that can be divided into four basic operational blocks. For both encryption and decryption, the cipher begins with adding Round Key stage [30].

However, before reaching the final round, this output goes through nine main rounds, during each of those rounds four transformations are performed; 1- Subbytes, 2- Shift rows, 3- Mix-columns, 4- Add round Key.

In the final 10th round, there is no Mix-column transformation. Figure shows the overall process. Each round of AES is governed by the following transformations [12]: 3. In sub-byte transformation, each byte 8-bit of a data block is transformed into another block using an 8-bit substitution box, which is known as Rijndael Sbox [13]. Figure 2. DES is one of the most widely accepted, publicly available cryptographic systems.

The algorithm submitted to the National Bureau of Standards NBS to propose a candidate for the protection of sensitive unclassified electronic government data. It is now taken as unsecured cause of its small size and a brute force attack is possible in it. The key length is 56 bits and block size is 64 bit length. It is vulnerable to key attack when a weak key is used.

It began with a 64 bit key and then the NSA put a restriction to use of DES with a bit key length, hence DES discards 8 bits of the 64 bit key and then uses the compressed 56 bit key derived from 64 bits key to encrypt data in block size of 64bits. The algorithm is believed to be practically secure in the form of Triple DES, although there are theoretical attacks.

RSA is founded in is a public key cryptosystem. It is one of the best-known public key cryptosystems for key exchange or digital signatures or encryption of blocks of data. RSA uses a variable size encryption block and a variable size key. It is an asymmetric public key cryptosystem based on number theory, which is a block cipher system. It uses two prime numbers to generate the public and private keys size is to bits. These two different keys are used for encryption and decryption purpose.

Sender encrypts the message using Receiver public key and when the message gets transmit to receiver, then receiver can decrypt it by using his own private key [20,21]. RSA operations can be decomposed in three broad steps; key generation, encryption and decryption. RSA have many flaws in its design therefore not preferred for the commercial use. Figure illustrates the sequence of events followed by RSA algorithm for the encryption of multiple blocks.

Decrypt blocks of data consisting of 64 bits by using a bit key [22]. Figure 3. Blowfish was first published in [6]. It is a symmetric key block cipher with key length variable from 32 to bits and block size of 64 bits. Its structure is fiestal network. It takes a variable-length key, from 32 bits to bits, making it ideal for both domestic and commercial use [8]. Blowfish was designed by Bruce Schneier as a fast, free alternative to existing encryption algorithms.

From then, it has been analyzed considerably, and it is slowly gaining popularity as a robust encryption algorithm. Blowfish is not patented, has free license and is freely available for all uses [24].

In this paper, the results are analyzed based on the implementation that performed in [1,27].

## Cryptography and Network Security: Principles and Practice, 5th Edition

Secure Sockets Layer SSL is a protocol developed by Netscape for establishing an encrypted link between a web server and a browser. SSL is an industry standard which transmits private data securely over the Internet by encrypting it. It is used by many websites to protect the online transactions of their customers. Description: SSL functions around a cryptographic system which uses three keys t. Cross-site scripting XSS is a type of computer security vulnerability. Description: Cross-site scripting XSS exploits the 'same-origin-policy' concept of web applications to allow hackers to extract information from the system. How it works: Attackers conduct script injection that runs at the client side and is sometimes.

Cryptography and Network Security Principles and Practices, Fourth Edition other relevant sites, transparency masters of figures and tables in the book in PDF (Adobe How-to: Advice and guidance for solving homework problems, writing.

## Cryptography Book By Forouzan Pdf Writer

Mobile security , or more specifically mobile device security , is the protection of smartphones, tablets, and laptops from threats associated with wireless computing. Of particular concern is the security of personal and business information now stored on smartphones. More and more users and businesses use smartphones to communicate, but also to plan and organize their users' work and also private life. Within companies, these technologies are causing profound changes in the organization of information systems and therefore they have become the source of new risks.

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