Two generally accepted design principles for practical ciphers are the principles of confusion and diffusion that were suggested by shannon. Merging of vigenere cipher with xtea block cipher to encryption digital documents. New paradigm design by merging the techniques of stream cipher. Many other slides are from dan bonehsjune 2012 coursera crypto class. Cryptography deals with various security principles which are as follows. Secure block ciphers cryptanalysis and design tiessen, tyge publication date. This is a result of inevitable tradeoffs required in practical applications, including. The major difference between a block cipher and a stream cipher is that the block cipher encrypts and decrypts a block. Assume cryptanalyst has access to blackbox implementing block cipher with secret key k aims of cryptanalyst.
Publickey block ciphers are discussed in chapter 8. Some of block cipher modes are used as a stream cipher mechanism. Using smaller blocks leads to important security issues when encrypting large messages or using the block cipher for a mac over such a large message. A constant intermixing of design principles, ciphers, and analysis would only make.
The proposed algorithm will be used a variable key size. Block cipher and stream cipher are the methods used for converting the plain text into cipher text directly and belong to the family of symmetric key ciphers. Round function repeated several times rounds first round takes nbit plaintext as input last round outputs nbit cipher text each round depends on a roundkey derived from kbit secret key key schedule. The techniques discussed are applicable with any block cipher and any stream cipher. Ktantan is a block cipher which accepts an 80bit usersupplied key. Block cipher design priciples free download as powerpoint presentation. Block ciphers and the data encryption standard block vs stream.
In this research we attempt to merge some of block cipher techniques that make the block ciphers harder in cryptanalysis. Use a linear key schedule, combining bit permutations and. Merging of vigenere cipher with xtea block cipher to. Difference between block cipher and stream cipher with. 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. Many symmetric block encryption algorithms in current use are based on a structure referred to as a feistel block cipher feis73.
Block cipher is an encryption algorithm which takes fixed size of input say b bits and produces a ciphertext of b bits again. In a block cipher a block of symbols from m is operated on jointly by the encryption algorithm, so that in general one may view a block cipher as a nonsingular i. This hardware design is applied to the new secret and variable size key block cipher called blowfish designed to meet the requirements of the previous known standard and to increase security and to improve performance. January 17, 2012 3 block cipher principles stream cipher is one that encrypts a digital data stream one bit or byte at a time example. A block cipher design can be divided in feistel and spn design 15. This block cipher is weak because it is purely linear and. We take a step back, and try to merge the ciphers from an algorithmic point of view.
Symmetric block cipher with a block length of 128 bits and support for key lengths of 128, 192, and 256 bits. In this paper we introduce three developments of block cipher modes of operation. We begin with a comparison of stream ciphers and block ciphers. Block cipher design principles these slides are based partly on lawrie browns s slides supplied with william stallings book cryptography and network security. After developing the principles of block ciphers over several years, ibm. Design principles of block ciphers and differential attacks 2. In this paper, we propose a new stream cipher construction based on block cipher design principles. Thus, efficiency is the most important additional design criterion for professional ciphers. Pdf merging of vigenere cipher with xtea block cipher to. One possible attack under these circumstances is the bruteforce approach of trying all possible keys. To cryptanalyse present lightweight block cipher using. No block cipher is ideally suited for all applications, even one offering a high level of security. Stream and block cipher cryptography and network security.
Designing integrated accelerator for stream ciphers. Tea, xtea have a principle that stands out is small, secure, simple and fast, the. Symmetric and asymmetric encryption princeton university. New paradigm design by merging the techniques of stream. Symmetrickey block ciphers are the most fundamental elements in many. If input is larger than b bits it can be divided further. A block cipher processes the input one block of elements at a time, producing an output block for each input block. Network security block cipher modes of operation duration. Although much progress has been made in designing block ciphers that are cryptographically strong, the basic principles have not changed all that much since the work of feistel and the des design team in the early 1970s. Pdf design of enhanced speed blowfish algorithm for. Most popular and prominent block ciphers are listed below. For that reason, it is important to examine the design principles of the feistel cipher.
Block cipher design priciples cipher secure communication. Each block of 4 bits in the plaintext is transformed into a block of 4 ciphertext bits. Our new block cipher is based on aeslike design principles and this allows us to derive very simple bounds on the number of active sboxes during a block cipher encryption. Cryptography and network security principles and practices. There are some applications of mitm principles to block ciphers like des or aes, see e. For any given key k, a block cipher specifies an encryption algorithm for. The main idea is to replace the building blocks used in block ciphers by equivalent stream cipher components. Chapter 3 block ciphers and the data encryption standard all the afternoon mungo had been working on sterns code, principally with the aid of the latest. Chapter 3 block ciphers and the cryptography and data.
A stream cipher processes the input elements continuously, producing output one element at a time, as it goes along. The concepts and design principles of block ciphers are explained, particularly the class of block ciphers known as feistel ciphers. Apart from that, it seems that modern stream ciphers share a. Basic principles generally speaking, symmetric cryptosystems are divided into two types. Pdf the block cipher algorithmproperties, encryption efficiency. Stream cipher is faster than block cipher and works online. Given one of the standard iterated block cipher design schemes, it is fairly easy to construct a block cipher that is cryptographically secure, simply by using a large number of rounds.
In principle, they might give good security in a highperformance design. Computer and network security by avi kak lecture3 to 16 output integers. Development of block cipher modes of operations request pdf. The linear roundapproximations are usually found by combining several. The major difference between a block cipher and a stream cipher is that the block cipher encrypts and decrypts a block of the text at a time. Trivium a stream cipher construction inspired by block. This block is copied into the state array, which is modified at each stage of encryption or decryption. Modern block ciphers typically use a block length of 128 bits or more examples of block ciphers include des, aes, rc6, and idea a block cipher breaks message into fixed sized blocks takes one block plaintext at a time and transform it into another block of the same length using a user provided secret key decryption is. Designing integrated accelerator for stream ciphers with.
In this paper, we discuss some of theory of provable security against differential and linear cryptanalysis. For different applications and uses, there are several modes of operations for a block cipher. It is useful to begin this discussion by looking at the published design criteria used in. Block ciphers such as aes1 or des2 typically operate on large input data blocks, each consisting of 64 or more bits 128 or 256 bits are now preferred.
Trivium a stream cipher construction inspired by block cipher design principles. Since the key schedule is very simple, this analysis can be done in a relatedkey model as well. Caesar cipher, monoalphabetic cipher, homophonic substitution cipher, polyalphabetic cipher, playfair cipher, rail fence, one time pad, hill cipher are some of the examples of cryptography techniques. There are two principles which can be used in block cipher to make it secure. There is a vast number of block ciphers schemes that are in use. Salsa2012 is the only one that follows a block cipher like state update which is completely di. Command tradoc basic cryptanalysis field manual tra90. After the final stage, state is copied to an output matrix. Cryptanalysis of the lightweight block cipher ktantan. In order to illustrate this approach, we construct a very simple synchronous stream cipher which provides a lot of exibility for. Block cipher principles most symmetric block ciphers are based on a feistel cipher structure needed since must be able to decrypt ciphertext to recover messages efficiently block ciphers look like an extremely large substitution would need table of 264 entries for a 64bit block instead create from smaller building blocks. Block ciphers operate an enciphering transformation on each \message block independently, for example every 64bit string in des. Figure 1 depicts an ideal block cipher that uses blocks of size 4.