Symmetric Cryptography: DES And
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Chapter 3 – Block Ciphers and the Data Encryption Standard
Chapter 3 –Block Ciphers and the Data Cryptography and Network Encryption Standard Security All the afternoon Mungo had been working on Stern's Chapter 3 code, principally with the aid of the latest messages which he had copied down at the Nevin Square drop. Stern was very confident. He must be well aware London Central knew about that drop. It was obvious Fifth Edition that they didn't care how often Mungo read their messages, so confident were they in the by William Stallings impenetrability of the code. —Talking to Strange Men, Ruth Rendell Lecture slides by Lawrie Brown Modern Block Ciphers Block vs Stream Ciphers now look at modern block ciphers • block ciphers process messages in blocks, each one of the most widely used types of of which is then en/decrypted cryptographic algorithms • like a substitution on very big characters provide secrecy /hii/authentication services – 64‐bits or more focus on DES (Data Encryption Standard) • stream ciphers process messages a bit or byte at a time when en/decrypting to illustrate block cipher design principles • many current ciphers are block ciphers – better analysed – broader range of applications Block vs Stream Ciphers 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 • bloc k cihiphers lklook like an extremely large substitution • would need table of 264 entries for a 64‐bit block • instead create from smaller building blocks • using idea of a product cipher 1 Claude -
Feistel Like Construction of Involutory Binary Matrices with High Branch Number
Feistel Like Construction of Involutory Binary Matrices With High Branch Number Adnan Baysal1,2, Mustafa C¸oban3, and Mehmet Ozen¨ 3 1TUB¨ ITAK_ - BILGEM,_ PK 74, 41470, Gebze, Kocaeli, Turkey, [email protected] 2Kocaeli University, Department of Computer Engineering, Faculty of Engineering, Institute of Science, 41380, Umuttepe, Kocaeli, Turkey 3Sakarya University, Faculty of Arts and Sciences, Department of Mathematics, Sakarya, Turkey, [email protected], [email protected] August 4, 2016 Abstract In this paper, we propose a generic method to construct involutory binary matrices from a three round Feistel scheme with a linear round function. We prove bounds on the maximum achievable branch number (BN) and the number of fixed points of our construction. We also define two families of efficiently implementable round functions to be used in our method. The usage of these families in the proposed method produces matrices achieving the proven bounds on branch numbers and fixed points. Moreover, we show that BN of the transpose matrix is the same with the original matrix for the function families we defined. Some of the generated matrices are Maximum Distance Binary Linear (MDBL), i.e. matrices with the highest achievable BN. The number of fixed points of the generated matrices are close to the expected value for a random involution. Generated matrices are especially suitable for utilising in bitslice block ciphers and hash functions. They can be implemented efficiently in many platforms, from low cost CPUs to dedicated hardware. Keywords: Diffusion layer, bitslice cipher, hash function, involution, MDBL matrices, Fixed points. 1 Introduction Modern block ciphers and hash functions use two basic layers iteratively to provide security: confusion and diffusion. -
Block Ciphers and the Data Encryption Standard
Lecture 3: Block Ciphers and the Data Encryption Standard Lecture Notes on “Computer and Network Security” by Avi Kak ([email protected]) January 26, 2021 3:43pm ©2021 Avinash Kak, Purdue University Goals: To introduce the notion of a block cipher in the modern context. To talk about the infeasibility of ideal block ciphers To introduce the notion of the Feistel Cipher Structure To go over DES, the Data Encryption Standard To illustrate important DES steps with Python and Perl code CONTENTS Section Title Page 3.1 Ideal Block Cipher 3 3.1.1 Size of the Encryption Key for the Ideal Block Cipher 6 3.2 The Feistel Structure for Block Ciphers 7 3.2.1 Mathematical Description of Each Round in the 10 Feistel Structure 3.2.2 Decryption in Ciphers Based on the Feistel Structure 12 3.3 DES: The Data Encryption Standard 16 3.3.1 One Round of Processing in DES 18 3.3.2 The S-Box for the Substitution Step in Each Round 22 3.3.3 The Substitution Tables 26 3.3.4 The P-Box Permutation in the Feistel Function 33 3.3.5 The DES Key Schedule: Generating the Round Keys 35 3.3.6 Initial Permutation of the Encryption Key 38 3.3.7 Contraction-Permutation that Generates the 48-Bit 42 Round Key from the 56-Bit Key 3.4 What Makes DES a Strong Cipher (to the 46 Extent It is a Strong Cipher) 3.5 Homework Problems 48 2 Computer and Network Security by Avi Kak Lecture 3 Back to TOC 3.1 IDEAL BLOCK CIPHER In a modern block cipher (but still using a classical encryption method), we replace a block of N bits from the plaintext with a block of N bits from the ciphertext. -
Block Ciphers
Block Ciphers Chester Rebeiro IIT Madras CR STINSON : chapters 3 Block Cipher KE KD untrusted communication link Alice E D Bob #%AR3Xf34^$ “Attack at Dawn!!” message encryption (ciphertext) decryption “Attack at Dawn!!” Encryption key is the same as the decryption key (KE = K D) CR 2 Block Cipher : Encryption Key Length Secret Key Plaintext Ciphertext Block Cipher (Encryption) Block Length • A block cipher encryption algorithm encrypts n bits of plaintext at a time • May need to pad the plaintext if necessary • y = ek(x) CR 3 Block Cipher : Decryption Key Length Secret Key Ciphertext Plaintext Block Cipher (Decryption) Block Length • A block cipher decryption algorithm recovers the plaintext from the ciphertext. • x = dk(y) CR 4 Inside the Block Cipher PlaintextBlock (an iterative cipher) Key Whitening Round 1 key1 Round 2 key2 Round 3 key3 Round n keyn Ciphertext Block • Each round has the same endomorphic cryptosystem, which takes a key and produces an intermediate ouput • Size of the key is huge… much larger than the block size. CR 5 Inside the Block Cipher (the key schedule) PlaintextBlock Secret Key Key Whitening Round 1 Round Key 1 Round 2 Round Key 2 Round 3 Round Key 3 Key Expansion Expansion Key Key Round n Round Key n Ciphertext Block • A single secret key of fixed size used to generate ‘round keys’ for each round CR 6 Inside the Round Function Round Input • Add Round key : Add Round Key Mixing operation between the round input and the round key. typically, an ex-or operation Confusion Layer • Confusion layer : Makes the relationship between round Diffusion Layer input and output complex. -
Mirror Cipher Using Feistel Network
Mirror Cipher using Feistel Network 1 2 3 Ihsan Muhammad Asnadi Ranindya Paramitha Tony 123 Informatics Department, Institut Teknologi Bandung, Bandung 40132, Indonesia 1 2 3 E-mail: 1 [email protected] 1 [email protected] 1 [email protected] Abstract. Mirror cipher is a cipher built by creativity which has a specific feature of mirrored round function. As other ciphers, mirror cipher could be used to secure messages’ confidentiality and integrity. This cipher receives message and key inputs from its user. Then, it runs 9 rounds of feistel networks in ECB modes. Each round would run a round function which consists of 5 functions in mirrored order (9 function calls in total): s-box substitution, row substitution, column substitution, column cumulative xor, and round key addition. This cipher is implemented using Python and has been tested using several message and key combinations. Mirror cipher has applied Shanon’s diffusion and confusion property and proven to be secured from bruteforce and frequency analysis attack. 1. Introduction 1.1. Background In this modern world, data or messages are exchanged anytime and anywhere. To protect confidentiality and integrity of messages, people usually encrypt their messages before sending them, and then decrypt the received messages before reading them. These encryption and decryption practices and techniques are contained under the big concept of cryptography. There are many ciphers (encryption and decryption algorithms) that have been developed since the BC period. Ciphers are then divided into 2 kinds of ciphers, based on how it treats the message: stream cipher and block cipher. -
(SMC) MODULE of RC4 STREAM CIPHER ALGORITHM for Wi-Fi ENCRYPTION
InternationalINTERNATIONAL Journal of Electronics and JOURNAL Communication OF Engineering ELECTRONICS & Technology (IJECET),AND ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 79-85 © IAEME COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) IJECET ISSN 0976 – 6472(Online) Volume 6, Issue 1, January (2015), pp. 79-85 © IAEME: http://www.iaeme.com/IJECET.asp © I A E M E Journal Impact Factor (2015): 7.9817 (Calculated by GISI) www.jifactor.com VHDL MODELING OF THE SRAM MODULE AND STATE MACHINE CONTROLLER (SMC) MODULE OF RC4 STREAM CIPHER ALGORITHM FOR Wi-Fi ENCRYPTION Dr.A.M. Bhavikatti 1 Mallikarjun.Mugali 2 1,2Dept of CSE, BKIT, Bhalki, Karnataka State, India ABSTRACT In this paper, VHDL modeling of the SRAM module and State Machine Controller (SMC) module of RC4 stream cipher algorithm for Wi-Fi encryption is proposed. Various individual modules of Wi-Fi security have been designed, verified functionally using VHDL-simulator. In cryptography RC4 is the most widely used software stream cipher and is used in popular protocols such as Transport Layer Security (TLS) (to protect Internet traffic) and WEP (to secure wireless networks). While remarkable for its simplicity and speed in software, RC4 has weaknesses that argue against its use in new systems. It is especially vulnerable when the beginning of the output key stream is not discarded, or when nonrandom or related keys are used; some ways of using RC4 can lead to very insecure cryptosystems such as WEP . Many stream ciphers are based on linear feedback shift registers (LFSRs), which, while efficient in hardware, are less so in software. -
Chapter 3 – Block Ciphers and the Data Encryption Standard
Symmetric Cryptography Chapter 6 Block vs Stream Ciphers • Block ciphers process messages into blocks, each of which is then en/decrypted – Like a substitution on very big characters • 64-bits or more • Stream ciphers process messages a bit or byte at a time when en/decrypting – Many current ciphers are block ciphers • Better analyzed. • Broader range of applications. Block vs Stream Ciphers Block Cipher Principles • Block ciphers look like an extremely large substitution • Would need table of 264 entries for a 64-bit block • Arbitrary reversible substitution cipher for a large block size is not practical – 64-bit general substitution block cipher, key size 264! • Most symmetric block ciphers are based on a Feistel Cipher Structure • Needed since must be able to decrypt ciphertext to recover messages efficiently Ideal Block Cipher Substitution-Permutation Ciphers • in 1949 Shannon introduced idea of substitution- permutation (S-P) networks – modern substitution-transposition product cipher • These form the basis of modern block ciphers • S-P networks are based on the two primitive cryptographic operations we have seen before: – substitution (S-box) – permutation (P-box) (transposition) • Provide confusion and diffusion of message Diffusion and Confusion • Introduced by Claude Shannon to thwart cryptanalysis based on statistical analysis – Assume the attacker has some knowledge of the statistical characteristics of the plaintext • Cipher needs to completely obscure statistical properties of original message • A one-time pad does this Diffusion -
A Novel Feistel Cipher Involving a Bunch of Keys Supplemented with XOR Operation
(IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 3, No. 12, 2012 A Novel Feistel Cipher Involving a Bunch of Keys Supplemented with XOR Operation V.U.K Sastry K. Anup Kumar Dean R&D, Department of Computer Science and Associate Professor, Department of Computer Science Engineering, Sreenidhi Institute of Science & Tech. and Engineering, SNIST, Hyderabad, India Hyderabad, India Abstract—In this investigation, we have developed a novel block In order to satisfy (1.5), we chose ejk as an odd integer, cipher by modifying classical Feistel cipher. In this, we have used which lies in the interval [1-255], and thus we obtain djk also as a key bunched wherein each key has a multiplicative inverse. The an odd integer lying in the interval [1-255]. cryptanalysis carried out in this investigation clearly shows that this cipher cannot be broken by any attack. Here also we adopt an iterative procedure, and make use of the permutation process that consists of the interchange of the Keywords-encryption; decryption; cryptanalysis; avalanche effect; two halves of the plaintext , of course, represented in the form multiplicative inverse. of a pair of matrices. I. INTRODUCTION In the present analysis, our objective is to modify the Feistel cipher by including a bunch of keys. Here our interest is The study of the Feistel cipher [1-2] laid the foundation for to see how the different keys, occurring in the key bunch, the development of cryptography in the seventies of the last would influence the strength of the cipher. century. In the classical Feistel cipher the block size is 64 bits, and it is divided into two halves wherein each half is containing In what follows, we present the plan of the paper. -
A Practical Attack on Broadcast RC4
A Practical Attack on Broadcast RC4 Itsik Mantin and Adi Shamir Computer Science Department, The Weizmann Institute, Rehovot 76100, Israel. {itsik,shamir}@wisdom.weizmann.ac.il Abstract. RC4is the most widely deployed stream cipher in software applications. In this paper we describe a major statistical weakness in RC4, which makes it trivial to distinguish between short outputs of RC4 and random strings by analyzing their second bytes. This weakness can be used to mount a practical ciphertext-only attack on RC4in some broadcast applications, in which the same plaintext is sent to multiple recipients under different keys. 1 Introduction A large number of stream ciphers were proposed and implemented over the last twenty years. Most of these ciphers were based on various combinations of linear feedback shift registers, which were easy to implement in hardware, but relatively slow in software. In 1987Ron Rivest designed the RC4 stream cipher, which was based on a different and more software friendly paradigm. It was integrated into Microsoft Windows, Lotus Notes, Apple AOCE, Oracle Secure SQL, and many other applications, and has thus become the most widely used software- based stream cipher. In addition, it was chosen to be part of the Cellular Digital Packet Data specification. Its design was kept a trade secret until 1994, when someone anonymously posted its source code to the Cypherpunks mailing list. The correctness of this unofficial description was confirmed by comparing its outputs to those produced by licensed implementations. RC4 has a secret internal state which is a permutation of all the N =2n possible n bits words. -
Lecture Four
Lecture Four Today’s Topics . Historic Symmetric ciphers . Modern symmetric ciphers . DES, AES . Asymmetric ciphers . RSA . Next class: Protocols Example Ciphers . Shift cipher: each plaintext characters is replaced by a character k to the right. (When k=3, it’s a Caesar cipher). “Watch out for Brutus!” => “Jngpu bhg sbe Oehghf!” . Only 25 choices! Not hard to break by brute force. Substitution Cipher: each character in plaintext is replaced by a corresponding character of ciphertext. E.g., cryptograms in newspapers. plaintext code: a b c d e f g h i f k l m n o p q r s t u v w x y z ciphertext code: m n b v c x z a s d f g h j k l p o i u y t r e w q . 26! Possible pairs. Is is really that hard to break? Substitution ciphers . The Caesar cipher has a small key space, but doesn’t create a statistical independence between the plaintext and the ciphertext. The best ciphers allow no statistical attacks, thereby forcing a brute force, exhaustive search; all the security lies with the key space. As cryptographic algorithms matured, the statistical independence between the plaintext and cipher text increased. Ciphers . The caesar cipher, hill cipher, and playfair cipher all work with a single alphabet for doing substitutions . They are monoalphabetic substitutions. A more complex (and more robust) alternative is to use different substitution mappings on various portions of the plaintext. Polyalphabetic substitutions. More ciphers . Vigenère cipher: each character of plaintext is encrypted with a different a cipher key. -
A Tutorial on the Implementation of Block Ciphers: Software and Hardware Applications
A Tutorial on the Implementation of Block Ciphers: Software and Hardware Applications Howard M. Heys Memorial University of Newfoundland, St. John's, Canada email: [email protected] Dec. 10, 2020 2 Abstract In this article, we discuss basic strategies that can be used to implement block ciphers in both software and hardware environments. As models for discussion, we use substitution- permutation networks which form the basis for many practical block cipher structures. For software implementation, we discuss approaches such as table lookups and bit-slicing, while for hardware implementation, we examine a broad range of architectures from high speed structures like pipelining, to compact structures based on serialization. To illustrate different implementation concepts, we present example data associated with specific methods and discuss sample designs that can be employed to realize different implementation strategies. We expect that the article will be of particular interest to researchers, scientists, and engineers that are new to the field of cryptographic implementation. 3 4 Terminology and Notation Abbreviation Definition SPN substitution-permutation network IoT Internet of Things AES Advanced Encryption Standard ECB electronic codebook mode CBC cipher block chaining mode CTR counter mode CMOS complementary metal-oxide semiconductor ASIC application-specific integrated circuit FPGA field-programmable gate array Table 1: Abbreviations Used in Article 5 6 Variable Definition B plaintext/ciphertext block size (also, size of cipher state) κ number -
Symmetric Key Ciphers Objectives
Symmetric Key Ciphers Debdeep Mukhopadhyay Assistant Professor Department of Computer Science and Engineering Indian Institute of Technology Kharagpur INDIA -721302 Objectives • Definition of Symmetric Types of Symmetric Key ciphers – Modern Block Ciphers • Full Size and Partial Size Key Ciphers • Components of a Modern Block Cipher – PBox (Permutation Box) – SBox (Substitution Box) –Swap – Properties of the Exclusive OR operation • Diffusion and Confusion • Types of Block Ciphers: Feistel and non-Feistel ciphers D. Mukhopadhyay Crypto & Network Security IIT Kharagpur 1 Symmetric Key Setting Communication Message Channel Message E D Ka Kb Bob Alice Assumptions Eve Ka is the encryption key, Kb is the decryption key. For symmetric key ciphers, Ka=Kb - Only Alice and Bob knows Ka (or Kb) - Eve has access to E, D and the Communication Channel but does not know the key Ka (or Kb) Types of symmetric key ciphers • Block Ciphers: Symmetric key ciphers, where a block of data is encrypted • Stream Ciphers: Symmetric key ciphers, where block size=1 D. Mukhopadhyay Crypto & Network Security IIT Kharagpur 2 Block Ciphers Block Cipher • A symmetric key modern cipher encrypts an n bit block of plaintext or decrypts an n bit block of ciphertext. •Padding: – If the message has fewer than n bits, padding must be done to make it n bits. – If the message size is not a multiple of n, then it should be divided into n bit blocks and the last block should be padded. D. Mukhopadhyay Crypto & Network Security IIT Kharagpur 3 Full Size Key Ciphers • Transposition Ciphers: – Involves rearrangement of bits, without changing value. – Consider an n bit cipher – How many such rearrangements are possible? •n! – How many key bits are necessary? • ceil[log2 (n!)] Full Size Key Ciphers • Substitution Ciphers: – It does not transpose bits, but substitutes values – Can we model this as a permutation? – Yes.