Author: Goutam Paul ISBN: 359 Genre: Computers File Size: 59.82 MB Format: PDF, Docs Download: 712 Read: 239 RC4 Stream Cipher and Its Variants is the first book to fully cover the popular software stream cipher RC4. With extensive expertise in stream cipher cryptanalysis and RC4 research, the authors focus on the analysis and design issues of RC4. They also explore variants of RC4 and the eSTREAM finalist HC-128. After an introduction to the vast field of cryptology, the book reviews hardware and software stream ciphers and describes RC4. It presents a theoretical analysis of RC4 KSA, discussing biases of the permutation bytes toward secret key bytes and absolute values. The text explains how to reconstruct the secret key from known state information and analyzes the RC4 PRGA in detail, including a sketch of state recovery attacks. The book then describes three popular attacks on RC4: distinguishing attacks, Wired Equivalent Privacy (WEP) protocol attacks, and fault attacks.
The authors also compare the advantages and disadvantages of several variants of RC4 and examine stream cipher HC-128, which is the next level of evolution after RC4 in the software stream cipher paradigm. The final chapter emphasizes the safe use of RC4. With open research problems in each chapter, this book offers a complete account of the most current research on RC4. Category: Computers. Author: Andreas Klein ISBN: 794 Genre: Computers File Size: 73.19 MB Format: PDF, Kindle Download: 887 Read: 310 In cryptography, ciphers is the technical term for encryption and decryption algorithms. They are an important sub-family that features high speed and easy implementation and are an essential part of wireless internet and mobile phones. Unlike block ciphers, stream ciphers work on single bits or single words and need to maintain an internal state to change the cipher at each step.
Pdf Book Rc4 Stream Cipher And Its Variants Download Rc4 Stream Cipher And Its Variants. RC4 stream cipher and possible attacks on WEP. Rk is the WEP or root key and IV is the.
Typically stream ciphers can reach higher speeds than block ciphers but they can be more vulnerable to attack. Here, mathematics comes into play. Number theory, algebra and statistics are the key to a better understanding of stream ciphers and essential for an informed decision on their safety. Since the theory is less developed, stream ciphers are often skipped in books on cryptography. This book fills this gap. It covers the mathematics of stream ciphers and its history, and also discusses many modern examples and their robustness against attacks.
Part I covers linear feedback shift registers, non-linear combinations of LFSRs, algebraic attacks and irregular clocked shift registers. Part II studies some special ciphers including the security of mobile phones, RC4 and related ciphers, the eStream project and the blum-blum-shub generator and related ciphers. Stream Ciphers requires basic knowledge of algebra and linear algebra, combinatorics and probability theory and programming.
Appendices in Part III help the reader with the more complicated subjects and provides the mathematical background needed. It covers, for example, complexity, number theory, finite fields, statistics, combinatorics. Stream Ciphers concludes with exercises and solutions and is directed towards advanced undergraduate and graduate students in mathematics and computer science. Category: Computers. Author: Alasdair McAndrew ISBN: 716 Genre: Computers File Size: 28.73 MB Format: PDF, ePub, Docs Download: 641 Read: 271 Once the privilege of a secret few, cryptography is now taught at universities around the world. Introduction to Cryptography with Open-Source Software illustrates algorithms and cryptosystems using examples and the open-source computer algebra system of Sage.
The author, a noted educator in the field, provides a highly practical learning experience by progressing at a gentle pace, keeping mathematics at a manageable level, and including numerous end-of-chapter exercises. Focusing on the cryptosystems themselves rather than the means of breaking them, the book first explores when and how the methods of modern cryptography can be used and misused. It then presents number theory and the algorithms and methods that make up the basis of cryptography today. After a brief review of 'classical' cryptography, the book introduces information theory and examines the public-key cryptosystems of RSA and Rabin’s cryptosystem. Other public-key systems studied include the El Gamal cryptosystem, systems based on knapsack problems, and algorithms for creating digital signature schemes. The second half of the text moves on to consider bit-oriented secret-key, or symmetric, systems suitable for encrypting large amounts of data.
The author describes block ciphers (including the Data Encryption Standard), cryptographic hash functions, finite fields, the Advanced Encryption Standard, cryptosystems based on elliptical curves, random number generation, and stream ciphers. The book concludes with a look at examples and applications of modern cryptographic systems, such as multi-party computation, zero-knowledge proofs, oblivious transfer, and voting protocols. Category: Computers. Author: Jonathan Katz ISBN: 269 Genre: Computers File Size: 90.66 MB Format: PDF, Mobi Download: 281 Read: 1080 Cryptography is ubiquitous and plays a key role in ensuring data secrecy and integrity as well as in securing computer systems more broadly. Introduction to Modern Cryptography provides a rigorous yet accessible treatment of this fascinating subject. The authors introduce the core principles of modern cryptography, with an emphasis on formal definitions, clear assumptions, and rigorous proofs of security. The book begins by focusing on private-key cryptography, including an extensive treatment of private-key encryption, message authentication codes, and hash functions.
The authors also present design principles for widely used stream ciphers and block ciphers including RC4, DES, and AES, plus provide provable constructions of stream ciphers and block ciphers from lower-level primitives. The second half of the book covers public-key cryptography, beginning with a self-contained introduction to the number theory needed to understand the RSA, Diffie-Hellman, and El Gamal cryptosystems (and others), followed by a thorough treatment of several standardized public-key encryption and digital signature schemes. Author: Gregory Bard ISBN: 579 Genre: Computers File Size: 79.10 MB Format: PDF, Docs Download: 627 Read: 667 Algebraic Cryptanalysis bridges the gap between a course in cryptography, and being able to read the cryptanalytic literature.
This book is divided into three parts: Part One covers the process of turning a cipher into a system of equations; Part Two covers finite field linear algebra; Part Three covers the solution of Polynomial Systems of Equations, with a survey of the methods used in practice, including SAT-solvers and the methods of Nicolas Courtois. Topics include: Analytic Combinatorics, and its application to cryptanalysis The equicomplexity of linear algebra operations Graph coloring Factoring integers via the quadratic sieve, with its applications to the cryptanalysis of RSA Algebraic Cryptanalysis is designed for advanced-level students in computer science and mathematics as a secondary text or reference book for self-guided study. This book is suitable for researchers in Applied Abstract Algebra or Algebraic Geometry who wish to find more applied topics or practitioners working for security and communications companies. Category: Computers. Author: Alfred J. Menezes ISBN: 916 Genre: Mathematics File Size: 52.68 MB Format: PDF, Mobi Download: 482 Read: 1226 Cryptography, in particular public-key cryptography, has emerged in the last 20 years as an important discipline that is not only the subject of an enormous amount of research, but provides the foundation for information security in many applications. Standards are emerging to meet the demands for cryptographic protection in most areas of data communications.
Public-key cryptographic techniques are now in widespread use, especially in the financial services industry, in the public sector, and by individuals for their personal privacy, such as in electronic mail. This Handbook will serve as a valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography. It is a necessary and timely guide for professionals who practice the art of cryptography.
RC4A is a slight modification of the simple RC4 stream cipher designed to strengthen it against a number of attacks. However in the paper, the second key k2 is only mentioned twice and provides only a loose description of what it should be: We take one randomly chosen key k1.
Another key k2 is also generated from a pseudorandom bit generator (e.g. RC4) using k1 as the seed. Applying the Key Scheduling Algorithm, as described in Fig. 1, we construct two S-boxes S1 and S2 using the keys k1 and k2 respectively.
The main thing here is that k2 is 'generated from a pseudorandom bit generator (e.g. RC4) using k1 as the seed', and S1 and S2 are constructed 'using the keys k1 and k2 respectively'. In source code implementations of RC4A I have come across two different ways of handling S2, none of which use a PRBG to produce k2.
This results in different output for the same input:. S-boxes S1 and S2 are exactly the same (using k1 for both).
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All 256 values of S-box S1 constitute the key k2 for S2. In a, it is suggested to use a 'nonce' for k2, which has the same length of k1 but doesn't explain how it is calculated from k1 as a seed (which is understood to be how k2 is produced). Finally, appears to show that k2 is produced by feeding a number of bytes from S1 into the original RC4 PRGA, producing a keystream: To be more specific, in KSA of RC4, the array S1 is initialized, using the secret key K. WK, 16 bytes of keystream, are generated from the array S1 in PRGA of RC4.
Then, the array S2 is initialized in KSA of RC4, using WK. I am assuming K refers to k1 and WK refers to k2 in the original article. Related pseudo-code: RC4KSA(K, S1) For i = 0 l – 1 WKi = RC4PRGA(S1) RC4KSA(WK, S2) One problem with this approach is that when calculating k2, the RC4 PRGA would swap values in S1, altering it. S1 is used in the RC4A PRGA and would produce a different keystream than if it had not been altered. This can be avoided by using a second copy of S1 for RC4 PRGA, leaving the original unaltered.
So there is ambiguity in how the second key for S2 is produced, with implementations differing in output keystream for same input. A few questions:.
Do the two differing implementations in practice undermine RC4A's security claims by not using a PRBG/PRGA to produce k2?. Does it matter what k2 is, how it's produced, or if it's the same as k1?. What is the proper way to produce k2 that all implementations should follow? Do the two differing implementations in practice undermine RC4A's security claims by not using a PRBG/PRGA to produce k2? I wouldn't think so. I get the impression that the authors just intend k2 to be derived from k1. They have not amended the algorithm so much as to use a different key schedule for k1.
That leads to the requirement to create a second permutation using the existing key scheduling algorithm, thus a different key has to be found from somewhere. The truth of this is proven by the fact that different implementations use different techniques. Frankly it's a little disappointing that the authors didn't address k2's generation more specifically.
Does it matter what k2 is, how it's produced, or if it's the same as k1? From a cursory inspection of fig.3, it appears that each alternate output comes from each state permutation. There doesn't seem to be any interaction between them. I posit that if k1 = k2 then the outputs would be identical pairs. This seems consistent with the authors' comments regarding improved security by having more variables.
A PRNG is as good a way as any, but. Ideally the inner state of the PRNG should be equivalent to the length of the key, but since a RC4 key can technically be 2048 bits, that's a problem. Few smallish XOR shift or LFSR PRNGs have such a large state. What is the proper way to produce k2 that all implementations should follow? Again, the fact that differing implementations use differing ways of generating k2 proves that there is no proper way to produce it. Proper would just be that k1 ≠ k2. My personal choice would be a simple 256 byte randomly generated S box.
Note: it is confusing that the authors use the term S box to refer to the internal state array. I'm suggesting a real S box so that k2 = SBOXk1 for all bytes. There is a wonderful alternative solution to both initial key stream bias and generation of the two states.
Two fully widened can be used. One derangement makes k1, and a second independent derangement makes k2. Since this is a new variant of RC4, there cannot be any backward compatibility for passwords anyway. This means that the entire key scheduling algorithm can be scrapped. And it's a perfect fit as a fully widened Pearson hash output is exactly 2048 bits.
Yes the maximum state size of such a hash is only 1684 bits, but who uses passwords that have 210 bytes of entropy anyway? Opinion on the paper I find section 5 very poor.
Every (even amateur) cryptographer knows that RC4's Achilles heel is bias. Indeed the authors' motivation is to improve RC4's security. This must mean bias reduction. So how can they possibly put forward an RC4 derivative without a bias assessment? What is the point of section 2 if they then just forget about possible biases of their own creation?
'Diminished' from section 5.3 is not good enough. It means nothing that their baby passes randomness tests. The original RC4 did too. This speaks to the vagueness and generality of current test suites, but also forms a cop out for the authors. I don't know if this is intentional. If they wanted a quick and dirty solution, all they had to do was add a von Neumann extractor after the PRNG component and RC4 becomes bias free. As pointed out in the comments to you, RC4A can be distinguished now via observation of.
The author's began their paper saying that the original RC4 could be distinguished after 2^25 outputs. They seem to have gone backwards, although in fairness attacks improve with time.