Plaintext Bits Research Articles

Generation of maximum length non-binary key sequence and its application for stream cipher based on residue number system

A cipher system in which the data is sequence of binary digits from data source and secrete key is also a random sequence of binary digits is called Stream cipher system. The stream cipher system which uses only binary information and key to get binary cipher text is known as binary stream cipher system. In this the encryption algorithm is bit by bit XOR operations of plain text bit and corresponding key sequence bit respectively. This concept further generalized to a non binary cipher system defined over any finite field GF (p), where p is prime integer. Again generalizing further it can also be defined a stream cipher system over the a ring Zm, arithmetic operations are carried out over modulo m, where m is suitable large composite integers and the ring is a set which satisfies closure, associative, distributive and commutative properties on addition and multiplication operation.The effectiveness of the non binary stream cipher system is based on different parameters mainly on encryption/decryption algorithm, key generation and its parameters. This paper concentrates on generating non binary key sequence of maximum length. This generated key is used for the application of Residue Number System (RNS) based stream cipher system. The properties like, uniformity, independence and maximum length for the key sequence is tested and verified. Also security issues of cipher systems using these key sequences for an image are tested and evaluated for its strength.

Efficient hierarchical identity based encryption scheme in the standard model over lattices

Using lattice basis delegation in a fixed dimension, we propose an efficient lattice-based hierarchical identity based encryption (HIBE) scheme in the standard model whose public key size is only (dm 2 + mn) log q bits and whose message-ciphertext expansion factor is only log q, where d is the maximum hierarchical depth and (n, m, q) are public parameters. In our construction, a novel public key assignment rule is used to averagely assign one random and public matrix to two identity bits, which implies that d random public matrices are enough to build the proposed HIBE scheme in the standard model, compared with the case in which 2d such public matrices are needed in the scheme proposed at Crypto 2010 whose public key size is (2dm 2 + mn +m) log q. To reduce the message-ciphertext expansion factor of the proposed scheme to log q, the encryption algorithm of this scheme is built based on Gentry’s encryption scheme, by which m 2 bits of plaintext are encrypted into m 2 log q bits of ciphertext by a one time encryption operation. Hence, the presented scheme has some advantages with respect to not only the public key size but also the message-ciphertext expansion factor. Based on the hardness of the learning with errors problem, we demonstrate that the scheme is secure under selective identity and chosen plaintext attacks.

Cryptanalysis of nonlinear feedback shift registers

ABSTRACTFor a successful cryptanalysis of an NLFSR, the needed number of known plaintext bits is about the smaller of two numbers: the period (including the preperiod if the sequence is not purely periodic) and the number of degrees of freedom of the feedback function. Therefore, under the assumption that the feedback function is completely unknown, there is no better way to cryptanalyse an NLFSR than a straightforward search for the period. If the choice of the feedback function is restricted in order to guarantee its efficient computation, then an algorithm by Boyar and Krawczyk gives an efficient cryptanalysis of the NLFSR in the sense of asymptotic complexity.

Advanced Feedback Encryption Standard Version-1 (AFES-1)

In this paper, Advanced Feedback Encryption Standard Version 1 (AFES-1), Nath et al have combined both bit-level and byte level operations on the plain text. Nath et al had recently published Multi Way Feedback Encryption Standard Ver-3 MWFES-3[5]. MWFES-3 is a byte level encryption algorithm. The authors have capitalized on the strength of MWFES-3[5] by introducing a bit-shuffling operation at the beginning of each iteration. At the beginning of each iteration, the plain text bits of that iteration are shuffled by using 24 different shuffling functions. Now, the order in which the 24 different functions are called, changes at each iteration, and that order is taken as a function of the key. After the initial shuffling of the bits, the bits are converted back to bytes and MWFES-3 is applied on the bytes. This process goes on Encryption Number (EN) times, where EN is also taken as a function of the key. So, at the beginning of each iteration, the bits obtained from the last iteration are shuffled in a different way. This method has been tested on standard plain texts such as ASCII ‘0’, ASCII ‘1’ and the results are quite satisfactory. This method is immune to any classical form of attacks. General Terms Encryption, Decryption.

A Novel Authenticated Cipher for RFID Systems

In this paper, we present RBS (Redundant Bit Securi ty) algorithm which is a low-complexity symmetric encryption with a 132-bit secret key. In this algorithm redundant bits are distributed among plaintext data bits to change the location of the plaintext bits in the transmitted data without changing their o rder. The location of redundant bits inside the transmitted data represents the secret key between sender and receiver. The algorithm provides integrity and authentication of the original data as well. The implementation comparison of this algorithm with other algorithms confirms thatit a good candidate for resource-constraint devices such as RFID systems and wireless sensors .

Cipher feedback mode under go‐back‐N and selective‐reject protocols in error channels

ABSTRACTTo produce ciphertexts, two modes of encryption are applied—block ciphers, which encrypt a fixed size block of plaintext at a time, and stream ciphers, which encrypt stream data, one or more bits at a time. As one of stream ciphers, the cipher feedback (CFB) mode is implemented by a block cipher via multiple stages, and in each stage, 1 bit or a number of bits of plaintext are encrypted at a time. Throughout this paper, the study will focus upon the error performance of the stream‐based CFB under two sliding‐window protocols, go‐back‐N and selective‐reject, in an error channel in terms of throughput. We model the performance of the CFB in terms of application‐level throughput and derive the number of stages needed to achieve the optimal throughput, under a given error rate in an error channel. Copyright © 2012 John Wiley & Sons, Ltd.

Applying cube attacks to stream ciphers in realistic scenarios

Cube attacks were introduced in Dinur and Shamir (2009) as a cryptanalytic technique that requires only black box access to the underlying cryptosystem. The attack exploits the existence of low degree polynomial representation of a single output bit (as a function of the key and plaintext bits) in order to recover the secret key. Although cube attacks can be applied in principle to almost any cryptosystem, most block ciphers iteratively apply a highly non-linear round function (based on Sboxes or arithmetic operations) a large number of times which makes them resistant to cube attacks. On the other hand, many stream ciphers (such as Trivium (De Canniere and Preneel 2008)), are built using linear or low degree components and are natural targets for cube attacks. In this paper, we describe in detail how to apply cube attacks to stream ciphers in various settings with different assumptions on the target stream cipher and on the data available to the attacker.

The Bit Security of Two Variants of Paillier Trapdoor Function

This paper gives the bit security analysis of two variants of Paillier's trapdoor function,Rabin-Paillier and RSA-Paillier.For Rabin-Paillier trapdoor function,it is shown that computing the 32n/2+log2n most significant bits(MSB) of its plaintext is as hard as inverting this function.The proof is based on a variant of Hidden Number Problem(HNP) over prime field introduced by Boneh et al.The authors extend this variant to Paillier modulus N2 case by using a new bound of exponential sum given by Malykhin in 2007.For the RSA-Paillier trapdoor function,the authors complete Morillo et al.'s proof on the hardness of the least significant bit of plaintext,and devise a randomization procedure to make their algorithm workable in an imperfect oracle case.

An Approach in Improving Transposition Cipher System

Transposition ciphers are stronger than simple substitution ciphers. However, if the key is short and the message is long, then various cryptanalysis techniques can be applied to break such ciphers. By adding 8 bits (one byte) for each byte using a function and another mathematical function to position the bits in a binary tree and using its in-order tour, this cipher can be made protected. Using an in-order tour of binary tree can diffuse the eight bits (includes 7 bits produced by the function and 1 random bit) and eight bits of the plaintext. This can highly protect the cipher. However, if the key management processes are not secured the strongest ciphers can easily be broken.

Counter Mode Development for Block Cipher Operations

There are two basic types of symmetric algorithms: block ciphers and stream ciphers. Block ciphers operate on blocks of plaintext and ciphertext—usually of 64 bits but sometimes longer. Stream ciphers operate on streams of plaintext and ciphertext one bit or byte (sometimes even one 32-bit word) at a time. With a block cipher, the same plaintext block will always encrypt to the same ciphertext block, using the same key. With a stream cipher, the same plaintext bit or byte will encrypt to a different bit or byte every time it is encrypted. In this paper we introduce three developments of Counter Mode of Operation of Block cipher. These developments merge between advantages of Counter Mode with other Modes. This gives a good secure Modes for General purpose block-oriented transmission Authentication, Random access, Stream-oriented transmission over noisy channel.

Stream-based cipher feedback mode in wireless error channel

Block ciphers encrypt a fixed size block of plaintext at a time to produce a block of ciphertext. Stream ciphers encrypt stream data, such as voice or Telnet traffic, one bit or more bits at a time. The cipher feedback mode is a stream cipher implemented by a block cipher via multiple stages, and in each stage one bit or a number of bits of plaintext are encrypted at a time. In this paper, we study error performance of the stream-based cipher feedback mode in an unreliable wireless channel in terms of throughput. We model performance of the cipher feedback mode in terms of the probability that part of or the whole ciphertext can not be successfully decrypted, and the throughput by adopting the cipher feedback mode. We explicitly derive the optimal number of stages in the cipher feedback mode to achieve the optimal throughput, given an error rate in a wireless network. We also prove that for the cipher feedback mode, the whole ciphertext is successfully decrypted if and only if the whole ciphertext is successfully transmitted.

A homophonic Rijndael

In this work, a variation of Rijndael is proposed. Rijndael algorithm is strengthened by adding some random bits into the plaintext. One random bit is added into each 7 bits of plaintext to form a byte. The three data block sizes of variation Rijndael are 112, 168 and 224 with three optional key sizes unchanged.

Information leakage of Feistel ciphers

We examine the information leakage between sets of plaintext and ciphertext bits in symmetric-key block ciphers. The paper demonstrates the effectiveness of information leakage as a measure of cipher security by relating information leakage to linear cryptanalysis and by determining a lower bound on the amount of data required in an attack from an upper bound on information leakage. As well, a model is developed which is used to estimate the upper bound on the information leakage of a general Feistel (1975) block cipher. For a cipher that fits the model well, the results of the analysis can be used as a measure in determining the number of rounds required for security against attacks based on information leakage. It is conjectured that the CAST-128 cipher fits the model well and using the model it is predicted that information leaked from 20 or fewer plaintext bits is small enough to make an attack on CAST-128 infeasible.

Nondegenerate functions and permutations

One of the basic design criteria for a block encryption function is to ensure that for each fixed key, each ciphertext bit depends nonlinearly on each plaintext bit. When the ciphertext is represented using boolean equations depending on the key and plaintext, these equations should then be nondegenerate so that it is possible that each bit of the key and plaintext can influence each ciphertext bit. We prove that nondegeneracy in a boolean function can be verified in linear time on average. We study higher order nondegeneracy and prove that for balanced n-bit functions, on average, at least n — [ log n]— 2 input bits must be held constant before a degenerate subfunction is induced. We also prove that the fraction of n-bit permutations within the symmetric group that are realized by nondegenerate boolean functions tends to one as n increases. Letting N n, n be the set of nondegenerate permutations, we formally prove that 1 −L n < ¦ N n,n¦2 n! < 1 − L n + U n, (1) where U n, L n ϵ o(1).

On a method of cryptanalysis for cryptosystem with involution

AbstractCryptology provides the technological basis for guaranteed network security. In the field of business, to guarantee the security of information, everyone needs easy‐to‐use cryptology. Starting with the announcement by the U.S. National Bureau of Standards of the DES cryptosystem and the proposal by NTT of the FEAL cryptosystem, secret‐key cryptographic algorithms have been published, involution‐type block cryptosystems which use secret key to encipher 64 bits of plain text as 64 bits of cipher text [2, 3, 9, 10, 12]. NTT has pro posed the one‐way function MAP, which is also an invo lution‐type transform. In this paper, we study a new cryptanalytic method for involution‐type cryptosystems and show by example that it can be applied practically in a ciphertext‐only attack on the one‐way function MAP. For an involution‐type cryptosystem, by increasing the amount of construction in the data‐randomization phase and by increasing the size of the secret key, we can guarantee the computational security by preventing the estimation of the secret key. However, if we study the properties of the function used in the design of the data‐ randomization phase, by specifying input/output values of the function which are independent of the secret key, it may be possible to use the inverse function [11] to calculate the secret key. This method is called the inter Mediate cipher method. the intermediate cipher method differs from previous methods in the small quantity of data required for breaking.

GeoSight fact finder, GIS based software package

The Data Encryption Standard (DES) or Data Encryption Algorithm (DEA), ANSI standard X3.92-1981, is a well known symmetric block cipher. In the basic mode of operation, electronic code book mode, it encrypts blocks of 64 bits of plain text into 64 bits of cipher text using a 56-bit key. Its internal structure, which is highly non-linear and contains 18 permutations and 16 expansions of bit blocks, does not encourage software implementation but is much better suited for hardware implementation. However, by a series of equivalence transformations, all expansions and but two of the permutations can be eliminated. Furthermore, then the 16-bit or 32-bit architecture of modern microprocessors can be fully exploited. Both a 16-bit version of the transformed algorithm (for 8086 and 80286) and a 32-bit version (for 80386 and 80486) have been implemented in assembly language. Depending on the actual processor employed, the implementation chooses 16-bit code or 32-bit code at run time. A sustained throughput of over 75,000 bytes second on a 33-MHz 80386 with cache and of over 8800 bytes per second on a 10-MHz 80286 with one wait state is obtained. The program needs only 13·3 kbytes for code and data. Hence this high-performance software DES implementation is also well suited for embedded applications, as for instance for encryption of serial communication lines or ISDN voice and data channels.

A high-performance software implementation of the Data Encryption Algorithm (DEA)

The Data Encryption Standard (DES) or Data Encryption Algorithm (DEA), ANSI standard X3.92-1981, is a well known symmetric block cipher. In the basic mode of operation, electronic code book mode, it encrypts blocks of 64 bits of plain text into 64 bits of cipher text using a 56-bit key. Its internal structure, which is highly non-linear and contains 18 permutations and 16 expansions of bit blocks, does not encourage software implementation but is much better suited for hardware implementation. However, by a series of equivalence transformations, all expansions and but two of the permutations can be eliminated. Furthermore, then the 16-bit or 32-bit architecture of modern microprocessors can be fully exploited. Both a 16-bit version of the transformed algorithm (for 8086 and 80286) and a 32-bit version (for 80386 and 80486) have been implemented in assembly language. Depending on the actual processor employed, the implementation chooses 16-bit code or 32-bit code at run time. A sustained throughput of over 75,000 bytes second on a 33-MHz 80386 with cache and of over 8800 bytes per second on a 10-MHz 80286 with one wait state is obtained. The program needs only 13·3 kbytes for code and data. Hence this high-performance software DES implementation is also well suited for embedded applications, as for instance for encryption of serial communication lines or ISDN voice and data channels.

TREE FUNCTIONS AND CIPHER SYSTEMS

A number of encryption systems work by combining each plaintext bit with a hash function of the last n ciphertext bits. Such systems are self-synchronising in that they recover from ciphertext errors with an error extension of n. We show firstly that if the hash function is a tree function, then the system is vulnerable to a chosen ciphertext attack and, under certain circumstances, to a chosen plaintext attack; secondly, that all hash functions are equivalent to some tree function; thirdly, that whether or not this gives a computable attack on a given algorithm depends on the connectivity of a graph associated with the hash function; and, fourthly, the implications for DES, for RSA key selection, and for algorithm design in general.

Data encryption unit

The Data Encryption Standard (DES) or Data Encryption Algorithm (DEA), ANSI standard X3.92-1981, is a well known symmetric block cipher. In the basic mode of operation, electronic code book mode, it encrypts blocks of 64 bits of plain text into 64 bits of cipher text using a 56-bit key. Its internal structure, which is highly non-linear and contains 18 permutations and 16 expansions of bit blocks, does not encourage software implementation but is much better suited for hardware implementation. However, by a series of equivalence transformations, all expansions and but two of the permutations can be eliminated. Furthermore, then the 16-bit or 32-bit architecture of modern microprocessors can be fully exploited. Both a 16-bit version of the transformed algorithm (for 8086 and 80286) and a 32-bit version (for 80386 and 80486) have been implemented in assembly language. Depending on the actual processor employed, the implementation chooses 16-bit code or 32-bit code at run time. A sustained throughput of over 75,000 bytes second on a 33-MHz 80386 with cache and of over 8800 bytes per second on a 10-MHz 80286 with one wait state is obtained. The program needs only 13·3 kbytes for code and data. Hence this high-performance software DES implementation is also well suited for embedded applications, as for instance for encryption of serial communication lines or ISDN voice and data channels.