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Block ciphers are fundamental to modern cryptography, in fact they are the most widely used cryptographic primitive — useful in their own right, and in the construction of other cryptographic mechanisms. In this book the authors provide a technically detailed, yet readable, account of the state of the art of block cipher analysis, design, and deployment. The authors first describe the most prominent block ciphers and give insights into their design.

They then consider the role of the cryptanalyst, the adversary, and provide an overview of some of the most important cryptanalytic methods. The book will be of value to graduate and senior undergraduate students of cryptography and to professionals engaged in cryptographic design. An important feature of the presentation is the authors' exhaustive bibliography of the field, each chapter closing with comprehensive supporting notes. Most of the public-key primitives are based on hard mathematical problems such as the integer factorization in the RSA algorithm and discrete logarithm problem in the DiffieHellman.

Therefore, their security are mathematically proven. In contrast, symmetric-key primitives are usually not constructed based on well-defined hard mathematical problems. Hence, in order to get some assurance in their claimed security properties, they must be studied against different types of cryptanalytic techniques. Our research is dedicated to the cryptanalysis of block ciphers. In particular, throughout this thesis, we investigate the security of some block ciphers constructed with new design strategies.

These new strategies include i employing simple round function, and modest key schedule, ii using another input called tweak rather than the usual two inputs of the block ciphers, the plaintext and the key, to instantiate different permutations for the same key. This type of block ciphers is called a tweakable block cipher, iii employing linear and non-linear components that are energy efficient to provide low energy consumption block ciphers, iv employing optimal diffusion linear transformation layer while following the AES-based construction to provide faster diffusion rate, and v using rather weak but larger S-boxes in addition to simple linear transformation layers to provide provable security of ARX-based block ciphers against single characteristic differential and linear cryptanalysis.

The results presented in this thesis can be summarized as follows: Initially, we analyze the security of two lightweight block ciphers, namely, Khudra and Piccolo against Meet-in-the-Middle MitM attack based on the Demirci and Selcuk approach exploiting the simple design of the key schedule and round function.

According to the designers, the best attack on Kiasu-BC covers 7 rounds. However, we exploited the tweak to present 8-round attack using MitM with efficient enumeration cryptanalysis.

Then, we improve the previous results of the impossible differential cryptanalysis on SKINNY exploiting the tweakey schedule and linear transformation layer. Afterwards, we study the security of new low energy consumption block cipher, namely, Midori where we present the longest impossible differential distinguishers that cover complete 7 rounds.

Then, we utilized 4 of these distinguishers to launch key recovery attack against 11 rounds of Midori to improve the previous results on this cipher using the impossible differential cryptanalysis. Then, using the truncated differential cryptanalysis, we are able to attack 13 rounds of Midori utilizing a round differential distinguisher. We also analyze Kuznyechik, the standard Russian federation block cipher, against MitM with efficient enumeration cryptanalysis where we improve the previous results on Kuznyechik, using MitM attack with efficient enumeration, by presenting 6-round attack.

Unlike the previous attack, our attack exploits the exact values of the coefficients of the MDS transformation that is used in the cipher. Finally, we present key recovery attacks using the multidimensional zero-correlation cryptanalysis against SPARX, which follows the long trail design strategy, to provide provable security of ARX-based block ciphers against single characteristic differential and linear cryptanalysis.

These DDOs can provide fast encryption without incurring excessive hardware costs in modern telecommunication networks. However, until now, with a few exceptions, most DDO-based ciphers have been poorly represented in available literature and have continued to remain known to only a small number of encryption experts. In Data-Driven Block Ciphers for Fast Telecommunication Systems, Nikolai Moldovyan and Alexander Moldovyan, major innovators and holders of several dozen international patents in encryption technology, provide the background and detail the applications needed to investigate new properties of PNs especially relevant to the improvement of modern wireless systems.

Furthermore, they propose a universal architecture involving controlled bit permutation instruction that will permit the performance of both data-driven permutations and an arbitrary prescribed fixed permutation in a single cycle. Immediately improved efficiency for current and future fast telecommunication systems and mobile networks Because of its simplicity and efficient use of current hardware, the embedding of this architecture is a highly attractive option for CPU manufacturers.

By detailing all the relevant information into a single volume for the first time, the authors of this book make that option more feasible than ever before. Covered is the meaning of cryptography in informational society, including two-key cryptography, cryptographic protocols, digital electronic signatures, and several well-known single-key ciphers. Also detailed are the issues concerning and the methods of dealing with designing fast block ciphers and special types of attacks using random hardware faults.

Nevertheless, we still heavily rely on symmetric-key primitives as they give high-speed performance.Chapter 3. Stream Ciphers and Block Ciphers. Motivation for the Feistel Cipher Structure. The Feistel Cipher. DES Encryption. DES Decryption. The Avalanche Effect. The Use of Bit Keys. Timing Attacks. Differential Cryptanalysis. Linear Cryptanalysis. DES Design Criteria. Number of Rounds. Design of Function F. Key Schedule Algorithm. Stern was very confident.

He must be well aware London Central knew about that drop. Such a structure consists of a number of identical rounds of processing. In each round, a substitution is performed on one half of the data being processed, followed by a permu-tation that interchanges the two halves.

The original key is expanded so that a different key is used for each round. It exhibits the classic Feistel structure. DES uses a bit block and a bit key. DES has been shown to be highly resistant to these two types of attack. The objective of this chapter is to illustrate the principles of modern symmetric ciphers. Although numerous symmetric ciphers have been developed since the introduction of DES, and although it is destined to be replaced by the Advanced Encryption Standard AESDES remains the most important such algorithm.

Furthermore, a detailed study of DES provides an understanding of the principles used in other symmetric ciphers. This chapter begins with a discussion of the general principles of symmetric block ciphers, which are the type of symmetric ciphers studied in this book with the exception of the stream cipher RC4 in Chapter 7.Many symmetric block encryption algorithms in current use are based on a structure referred to as a Feistel block cipher [FEIS73].

For that reason, it is important to examine the design principles of the Feistel cipher. We begin with a comparison of stream ciphers and block ciphers. Then we discuss the motivation for the Feistel block cipher structure. Finally, we discuss some of its implications.

Stream Ciphers and Block Ciphers. A stream cipher is one that encrypts a digital data stream one bit or one byte at a time.

In the ideal case, a one-time pad version of the Vernam cipher would be used Figure 2. If the cryptographic keystream is random, then this cipher is unbreakable by any means other than acquiring the keystream.

### The Data Encryption Standard

However, the keystream must be provided to both users in advance via some independent and secure channel. This introduces insurmountable logistical problems if the intended data traffic is very large.

Accordingly, for practical reasons, the bit-stream generator must be imple- mented as an algorithmic procedure, so that the cryptographic bit stream can be produced by both users. In this approach Figure 3. Now, the two users need only share the generating key, and each can produce the keystream. A block cipher is one in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length.

Typically, a block size of 64 or bits is used. As with a stream cipher, the two users share a symmetric encryption key Figure 3. Using some of the modes of operation explained in Chapter 6, a block cipher can be used to achieve the same effect as a stream cipher. Far more effort has gone into analyzing block ciphers. In general, they seem applicable to a broader range of applications than stream ciphers.

The vast majority of network-based symmetric cryptographic applications make use of block ciphers. Accordingly, the concern in this chapter, and in our discussions throughout the book of symmetric encryption, will primarily focus on block ciphers.

Motivation for the Feistel Cipher Structure. Such a transformation is called reversible, or nonsingular. In the latter case, a ciphertext of 01 could have been produced by one of two plain- text blocks.

So if we limit ourselves to reversible mappings, the number of different transformations is 2 n!. Figure 3. A 4-bit input produces one of 16 possible input states, which is mapped by the substitution cipher into a unique one of 16 possible output states, each of which is represented by 4 ciphertext bits.

This is the most general form of block cipher and can be used to define any reversible mapping between plaintext and ciphertext. Feistel refers to this as the ideal block cipherbecause it allows for the max- imum number of possible encryption mappings from the plaintext block [FEIS75].

But there is a practical problem with the ideal block cipher. Such systems, as we have seen, are vulnerable to a statistical analysis of the plaintext. This weakness is not inherent in the use of a substitution cipher but rather results from the use of a small block size. If n is sufficiently large and an arbitrary reversible substitution between plaintext and ciphertext is allowed, then the statistical characteristics of the source plaintext are masked to such an extent that this type of cryptanalysis is infeasible.The block cipher currently supports key lengths of, and bits.

Each encryption key size causes the algorithm to behave slightly differently, so the increasing key sizes not only offer a larger number of bits with which you can scramble the data, but also increase the complexity of the cipher algorithm. Blowfish block cipher Blowfish is a symmetric encryption algorithm designed in by Bruce Schneier as an alternative to existing encryption algorithms.

Blowfish has a bit block size and a variable key length — from 32 bits to bits. It is a round Feistel cipher and uses large key-dependent S-boxes. CAST is a popular bit block cipher which belongs to the class of encryption algorithms known as Feistel ciphers. It has the Feistel structure and utilizes eight fixed S-boxes. CAST supports variable key lenghts between 40 and bits.

CAST is resistant to both linear and differential cryptanalysis. Currently, there is no known way of breaking CAST short of brute force. DES encrypts and decrypts data in bit blocks, using a bit key.

It takes a bit block of plaintext as input and outputs a bit block of ciphertext. Since it always operates on blocks of equal size and it uses both permutations and substitutions in the algorithm. DES has 16 rounds, meaning the main algorithm is repeated 16 times to produce the ciphertext. It has been found that the number of rounds is exponentially proportional to the amount of time required to find a key using a brute-force attack.

So as the number of rounds increases, the security of the algorithm increases exponentially. It has been designed to resist differential and linear cryptanalysis as well as related key attacks. Serpent can work with different combinations of key lengths.

It uses a bit key consisting of 56 effective key bits and 8 parity bits. The size of the block for Triple-DES is 8 bytes. Triple-DES encrypts the data in 8-byte chunks. Triple DES algorithm is very secure major banks use it to protect valuable transactionsbut it is also very slow. Twofish block cipher Twofish is a symmetric block cipher. Twofish has a block size of bits and accepts keys of any length up to bits.

Twofish has key dependent S-boxes like Blowfish. Block ciphers Block ciphers transform a fixed-size block of data usually 64 bits into another fixed-size block possibly 64 bits long again using a function selected by the key. If the key, input block and output block all have n bits, a block cipher basically defines a one-to-one mapping from n-bit integers to permutations of n-bit integers.Many block ciphers have a Feistel structure consisting of number of identical rounds of processing.

It exhibits the classic Feistel structure and uses a 64bitblock and a bit key. Two important methods of cryptanalysis are differential cryptanalysis and linear cryptanalysis.

## Encryption ciphers and modes

Feistel Cipher Structure needed as it can decrypt ciphertext to recover messages efficiently block ciphers look like an extremely large substitution would need table of entries for a bit block To avoid the difficulties instead create from smaller building blocks. DES History IBM developed Lucifer cipher by team led by Feistel in late 60s used bit data blocks with bit key then redeveloped as a commercial cipher with.

DES Design Controversy although DES standard is public was considerable controversy over design in choice of bit key as Lucifer was bit and classification of design criteria.

DES Decryption Decrypt uses same alg. Only the application of the subkeys is. Avalanche Effect key desirable property of encryption alg where a change of one input or key bit results. Strength of DES Timing Attacks attacks actual implementation of cipher use knowledge of consequences of. Linear Cryptanalysis another recent development also a statistical method must be iterated over rounds, with decreasing. Linear Cryptanalysis find linear approximations with prob p!

Learn more about Scribd Membership Home. Read Free For 30 Days. Much more than documents. Discover everything Scribd has to offer, including books and audiobooks from major publishers. Start Free Trial Cancel anytime. Uploaded by Sabin Bhandari. Document Information click to expand document information Description: Cryptography. Date uploaded Apr 06, Original Title Cryptography.

Did you find this document useful? Is this content inappropriate? Report this Document.Cryptography is an indispensable tool for protecting information in computer systems.

In this course you will learn the inner workings of cryptographic systems and how to correctly use them in real-world applications. The course begins with a detailed discussion of how two parties who have a shared secret key can communicate securely when a powerful adversary eavesdrops and tampers with traffic. We will examine many deployed protocols and analyze mistakes in existing systems. The second half of the course discusses public-key techniques that let two parties generate a shared secret key.

Throughout the course participants will be exposed to many exciting open problems in the field and work on fun optional programming projects. In a second course Crypto II we will cover more advanced cryptographic tasks such as zero-knowledge, privacy mechanisms, and other forms of encryption. This course gives is perfect to start learning cryptography, explanations are detailed, topics carefully selected combining theory with real world examples and making emphasis in important details.

A really interesting and in-depth course. The course could use more study materials, for example lecture notes. Week 2. We introduce a new primitive called a block cipher that will let us build more powerful forms of encryption. Block ciphers are the work horse of cryptography and have many applications. Next week we will see how to use block ciphers to provide data integrity. Loupe Copy. Cryptography I. Enroll for Free. From the lesson. The Data Encryption Standard Exhaustive Search Attacks More Attacks on Block Ciphers Taught By.

Dan Boneh Professor. Try the Course for Free. Explore our Catalog Join for free and get personalized recommendations, updates and offers.The cipher and mode that is used is randomly selected among the ciphers that are common between the two servers.

Make sure that all servers and client computers that participate in encrypted communication have ciphers and modes in common. Encryption is more secure if you include more ciphers and modes that the database server can switch between. For information about how to switch between ciphers, see Switch frequency. The Data Encryption Standard DES is a cryptographic algorithm designed to encrypt and decrypt data by using 8-byte blocks and a bit key.

DES3 works by first encrypting the plain text by using the first bits of the key. Then the cipher text is decrypted by using the next part of the key. In the final step, the resulting cipher text is re-encrypted by using the last part of the key. A Blowfish is a block cipher that operates on bit 8-byte blocks of data. It uses a variable size key, but typically, bit byte keys are considered to be good for strong encryption.

## Block Ciphers

Blowfish can be used in the same modes as DES. Use the allbut option to list ciphers and modes to exclude. The list can include unique, abbreviated entries. For example, bf can represent bf1bf2and bf3. However, if the abbreviation is the name of an actual cipher, then only that cipher is eliminated. Therefore, des eliminates only the DES cipher, but de eliminates desedeand desx.

Because ecb mode is considered weak; it is only included if specifically requested. It is not included in the all or the allbut list. You must specify which ciphers and mode to use during encryption. Two encryption modes are: Block Modea method of encryption in which the message is broken into blocks and the encryption occurs on each block as a unit.

**Block Ciphers and DES (CSS441, L05, Y15)**

Since each block is at least 8 bytes large, block mode provides the ability for bit arithmetic in the encryption algorithm. Stream Modea method of encryption in which each individual byte is encrypted.

It is generally considered to be a weak form of encryption. Important: You must not specify individual ciphers. For security reasons, all ciphers must be allowed. If a cipher is discovered to have a weakness, you can exclude it. The following desedeand desx ciphers are supported. Important: The cipher desx can only be used in cbc mode.

The following AES-encryption ciphers are supported. The following modes are supported. Parent topic: Communication support modules for data transmission encryption.

Related reference : Specifying network encryption options in concsm.