Cryptography
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Vigenère Cipher Cryptanalysis
Spring 2015 Chris Christensen MAT/CSC 483 Cryptanalysis of the Vigenère Cipher: Kasiski Test The keyword of a Vigenère cipher describes the rotation among the Caesar cipher alphabets that are used. That rotation leads to patterns that can be exploited by a cryptanalyst. If we know the length of the keyword, we can often determine the keyword and, hence, decrypt all messages encrypted with that keyword. Here is a ciphertext message that has been encrypted with a Vigenère cipher. nifon aicum niswt luvet vxshk nissx wsstb husle chsnv ytsro cdsoy nisgx lnona chvch gnonw yndlh sfrnh npblr yowgf unoca cossu ouoll iuvef issoe xgosa cpbew uormh lftaf cmwak bbbdv cqvek muvil qbgnh ntiri ljgig atwnv yuvev iorim cpbsb hxviv buvet vxshk uorim mjbdb pjrut fbueg ntgof yuwmx miodm ipdek uuswx lfjek sewfy yssnm zscmm bpgeb huvez ysaag usaew mffvb wfgim qpilw bbjeu yfbef vbfrt mtwnz uorig wpbvx hjsnm zpfag uhsnm npglb jbqrh mttrh huwek mpfak ljjen hbbnh ooqew vzdak udvum yucbx yoquf vffew vzonx hjumt lfgef vmwnz uxsiz bumag xbbtb kvotx xumpx qswtx l Assume that, somehow, we have discovered that the keyword has length five (which is conveniently the same as the size of the blocks). Then the first letter of each block is encrypted with the same row of the Vigenère square – they are encrypted with the same Caesar cipher. Similarly, the second letter of each block is encrypted with the same row – the same Caesar cipher. The third letters with the same Caesar cipher. The fourth letters with the same Caesar cipher. And, the fifth letters with the same Caesar cipher. -
Reconsidering the Security Bound of AES-GCM-SIV
Background on AES-GCM-SIV Fixing the Security Bound Improving Key Derivation Final Remarks Reconsidering the Security Bound of AES-GCM-SIV Tetsu Iwata1 and Yannick Seurin2 1Nagoya University, Japan 2ANSSI, France March 7, 2018 — FSE 2018 T. Iwata and Y. Seurin Reconsidering AES-GCM-SIV’s Security FSE 2018 1 / 26 Background on AES-GCM-SIV Fixing the Security Bound Improving Key Derivation Final Remarks Summary of the contribution • we reconsider the security of the AEAD scheme AES-GCM-SIV designed by Gueron, Langley, and Lindell • we identify flaws in the designers’ security analysis and propose a new security proof • our findings leads to significantly reduced security claims, especially for long messages • we propose a simple modification to the scheme (key derivation function) improving security without efficiency loss T. Iwata and Y. Seurin Reconsidering AES-GCM-SIV’s Security FSE 2018 2 / 26 Background on AES-GCM-SIV Fixing the Security Bound Improving Key Derivation Final Remarks Summary of the contribution • we reconsider the security of the AEAD scheme AES-GCM-SIV designed by Gueron, Langley, and Lindell • we identify flaws in the designers’ security analysis and propose a new security proof • our findings leads to significantly reduced security claims, especially for long messages • we propose a simple modification to the scheme (key derivation function) improving security without efficiency loss T. Iwata and Y. Seurin Reconsidering AES-GCM-SIV’s Security FSE 2018 2 / 26 Background on AES-GCM-SIV Fixing the Security Bound Improving Key Derivation Final Remarks Summary of the contribution • we reconsider the security of the AEAD scheme AES-GCM-SIV designed by Gueron, Langley, and Lindell • we identify flaws in the designers’ security analysis and propose a new security proof • our findings leads to significantly reduced security claims, especially for long messages • we propose a simple modification to the scheme (key derivation function) improving security without efficiency loss T. -
Elementary Cryptanalysis Classification of Cryptanalytic Attacks
12 Elementary Cryptography Elementary Cryptanalysis The most direct attack on a cryptosystem is an exhaustive key search attack. The key size therefore provides a lower bound on the security of a cryptosystem. As an example we compare the key sizes of several of the cryptosystems we have introduced so far. We assume that the alphabet for each is the 26 character alphabet. Substitution ciphers: Simple substitution ciphers: 26! Affine substitution ciphers: ϕ(26) · 26 = 12 · 26 = 312 Translation substitution ciphers: 26 Transposition ciphers: Transposition ciphers (of block length m): m! Enigma : Rotor choices (3 of 5): 60 Rotor positions: 263 = 17576 Plugboard settings: 105578918576 Total combinations: 111339304373506560 The size of the keyspace is a naive measure, but provides an upper bound on the security of a cryptosystem. This measure ignores any structure, like character frequencies, which might remain intact following encryption. Classification of Cryptanalytic Attacks We do not consider enumeration of all keys a valid cryptanalytic attack, since no well- designed cryptosystem is susceptible to such an approach. The types of legitimate attacks which we consider can be classified in three categories. 1. Ciphertext-only Attack. 2. Known Plaintext Attack. 3. Chosen Plainext Attack. Ciphertext-only Attack. The cryptanalyst intercepts one or more messages all encoded with the same encryption algorithm. Goal: Recover the original plaintext or plaintexts, to discover the deciphering key or find an algorithm for deciphering subsequent messages enciphered with the same key. Known Plaintext Attack. The cryptanalyst has access to not only the ciphertext, but also the plaintext for one or more of the messages. Goal: Recover the deciphering key or find an algorithm for deciphering subsequent mes- sages (or the remaining plaintext) enciphered which use the same key. -
State of the Art in Lightweight Symmetric Cryptography
State of the Art in Lightweight Symmetric Cryptography Alex Biryukov1 and Léo Perrin2 1 SnT, CSC, University of Luxembourg, [email protected] 2 SnT, University of Luxembourg, [email protected] Abstract. Lightweight cryptography has been one of the “hot topics” in symmetric cryptography in the recent years. A huge number of lightweight algorithms have been published, standardized and/or used in commercial products. In this paper, we discuss the different implementation constraints that a “lightweight” algorithm is usually designed to satisfy. We also present an extensive survey of all lightweight symmetric primitives we are aware of. It covers designs from the academic community, from government agencies and proprietary algorithms which were reverse-engineered or leaked. Relevant national (nist...) and international (iso/iec...) standards are listed. We then discuss some trends we identified in the design of lightweight algorithms, namely the designers’ preference for arx-based and bitsliced-S-Box-based designs and simple key schedules. Finally, we argue that lightweight cryptography is too large a field and that it should be split into two related but distinct areas: ultra-lightweight and IoT cryptography. The former deals only with the smallest of devices for which a lower security level may be justified by the very harsh design constraints. The latter corresponds to low-power embedded processors for which the Aes and modern hash function are costly but which have to provide a high level security due to their greater connectivity. Keywords: Lightweight cryptography · Ultra-Lightweight · IoT · Internet of Things · SoK · Survey · Standards · Industry 1 Introduction The Internet of Things (IoT) is one of the foremost buzzwords in computer science and information technology at the time of writing. -
Cryptography
Cryptography From Wikipedia, the free encyclopedia Jump to: navigation, search "Secret code" redirects here. For the Aya Kamiki album, see Secret Code. German Lorenz cipher machine, used in World War II to encrypt very-high-level general staff messages Cryptography (or cryptology; from Greek κρυπτός, kryptos, "hidden, secret"; and γράφ, gráph, "writing", or -λογία, -logia, respectively)[1] is the practice and study of hiding information. Modern cryptography intersects the disciplines of mathematics, computer science, and engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce. Cryptology prior to the modern age was almost synonymous with encryption, the conversion of information from a readable state to nonsense. The sender retained the ability to decrypt the information and therefore avoid unwanted persons being able to read it. Since WWI and the advent of the computer, the methods used to carry out cryptology have become increasingly complex and its application more widespread. Alongside the advancement in cryptology-related technology, the practice has raised a number of legal issues, some of which remain unresolved. Contents [hide] • 1 Terminology • 2 History of cryptography and cryptanalysis o 2.1 Classic cryptography o 2.2 The computer era • 3 Modern cryptography o 3.1 Symmetric-key cryptography o 3.2 Public-key cryptography o 3.3 Cryptanalysis o 3.4 Cryptographic primitives o 3.5 Cryptosystems • 4 Legal issues o 4.1 Prohibitions o 4.2 Export controls o 4.3 NSA involvement o 4.4 Digital rights management • 5 See also • 6 References • 7 Further reading • 8 External links [edit] Terminology Until modern times cryptography referred almost exclusively to encryption, which is the process of converting ordinary information (plaintext) into unintelligible gibberish (i.e., ciphertext).[2] Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. -
New Developments in Cryptology Outline Outline How NOT to Use A
New Developments in Cryptography February 2007 Bart Preneel Outline New developments in cryptology • 1. Cryptology: protocols – identification/entity authentication – key establishment Prof. Bart Preneel • 2. Public Key Infrastructures COSIC Bart.Preneel(at)esatDOTkuleuven.be • 3. Secure Networking protocols http://homes.esat.kuleuven.be/~preneel – Internet Security: email, web, IPSEC, SSL • 4. Using cryptography well • 5. New developments in cryptology © Bart Preneel. All rights reserved Outline How to use cryptographic algorithms • Modes of operation • Modes of operation • Padding and error messages • The hash function disaster • Authenticated encryption • How to encrypt using RSA • Algorithm: secure design and • How to encrypt with RSA implementation • Obfuscation • SPAM fighting How NOT to use a block cipher: ECB mode An example plaintext P1 P2 P3 block block block cipher cipher cipher C1 C2 C3 1 New Developments in Cryptography February 2007 Bart Preneel Encrypted with substitution and transposition cipher Encrypted with AES in ECB and CBC mode How to use a block cipher: CBC mode CBC mode decryption P1 P2 P3 P1 P2 P3 IV IV AES AES AES AES-1 AES-1 AES-1 C1 C2 C3 C1 C2 C3 What if IV is constant? CBC with incomplete plaintext (1) Plaintext length P2’ P3’ 1 byte P1 in bytes IV P1 P2 P3|| 0000..0 IV AES AES AES C1 C2’ C3’ AES AES AES Repetition in P results in repetition in C: ⇒ information leakage need random and secret IV C1 C2 C3 2 New Developments in Cryptography February 2007 Bart Preneel CBC with incomplete plaintext (2) CBC with -
A Hybrid Cryptosystem Based on Vigenère Cipher and Columnar Transposition Cipher
International Journal of Advanced Technology & Engineering Research (IJATER) www.ijater.com A HYBRID CRYPTOSYSTEM BASED ON VIGENÈRE CIPHER AND COLUMNAR TRANSPOSITION CIPHER Quist-Aphetsi Kester, MIEEE, Lecturer Faculty of Informatics, Ghana Technology University College, PMB 100 Accra North, Ghana Phone Contact +233 209822141 Email: [email protected] / [email protected] graphy that use the same cryptographic keys for both en- Abstract cryption of plaintext and decryption of cipher text. The keys may be identical or there may be a simple transformation to Privacy is one of the key issues addressed by information go between the two keys. The keys, in practice, represent a Security. Through cryptographic encryption methods, one shared secret between two or more parties that can be used can prevent a third party from understanding transmitted raw to maintain a private information link [5]. This requirement data over unsecured channel during signal transmission. The that both parties have access to the secret key is one of the cryptographic methods for enhancing the security of digital main drawbacks of symmetric key encryption, in compari- contents have gained high significance in the current era. son to public-key encryption. Typical examples symmetric Breach of security and misuse of confidential information algorithms are Advanced Encryption Standard (AES), Blow- that has been intercepted by unauthorized parties are key fish, Tripple Data Encryption Standard (3DES) and Serpent problems that information security tries to solve. [6]. This paper sets out to contribute to the general body of Asymmetric or Public key encryption on the other hand is an knowledge in the area of classical cryptography by develop- encryption method where a message encrypted with a reci- ing a new hybrid way of encryption of plaintext. -
Shift Cipher Substitution Cipher Vigenère Cipher Hill Cipher
Lecture 2 Classical Cryptosystems Shift cipher Substitution cipher Vigenère cipher Hill cipher 1 Shift Cipher • A Substitution Cipher • The Key Space: – [0 … 25] • Encryption given a key K: – each letter in the plaintext P is replaced with the K’th letter following the corresponding number ( shift right ) • Decryption given K: – shift left • History: K = 3, Caesar’s cipher 2 Shift Cipher • Formally: • Let P=C= K=Z 26 For 0≤K≤25 ek(x) = x+K mod 26 and dk(y) = y-K mod 26 ʚͬ, ͭ ∈ ͔ͦͪ ʛ 3 Shift Cipher: An Example ABCDEFGHIJKLMNOPQRSTUVWXYZ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 • P = CRYPTOGRAPHYISFUN Note that punctuation is often • K = 11 eliminated • C = NCJAVZRCLASJTDQFY • C → 2; 2+11 mod 26 = 13 → N • R → 17; 17+11 mod 26 = 2 → C • … • N → 13; 13+11 mod 26 = 24 → Y 4 Shift Cipher: Cryptanalysis • Can an attacker find K? – YES: exhaustive search, key space is small (<= 26 possible keys). – Once K is found, very easy to decrypt Exercise 1: decrypt the following ciphertext hphtwwxppelextoytrse Exercise 2: decrypt the following ciphertext jbcrclqrwcrvnbjenbwrwn VERY useful MATLAB functions can be found here: http://www2.math.umd.edu/~lcw/MatlabCode/ 5 General Mono-alphabetical Substitution Cipher • The key space: all possible permutations of Σ = {A, B, C, …, Z} • Encryption, given a key (permutation) π: – each letter X in the plaintext P is replaced with π(X) • Decryption, given a key π: – each letter Y in the ciphertext C is replaced with π-1(Y) • Example ABCDEFGHIJKLMNOPQRSTUVWXYZ πBADCZHWYGOQXSVTRNMSKJI PEFU • BECAUSE AZDBJSZ 6 Strength of the General Substitution Cipher • Exhaustive search is now infeasible – key space size is 26! ≈ 4*10 26 • Dominates the art of secret writing throughout the first millennium A.D. -
New Developments in Cryptology Outline Outline Block Ciphers AES
New Developments in Cryptography March 2012 Bart Preneel Outline New developments in cryptology • 1. Cryptology: concepts and algorithms Prof. Bart Preneel • 2. Cryptology: protocols COSIC • 3. Public-Key Infrastructure principles Bart.Preneel(at)esatDOTkuleuven.be • 4. Networking protocols http://homes.esat.kuleuven.be/~preneel • 5. New developments in cryptology March 2012 • 6. Cryptography best practices © Bart Preneel. All rights reserved 1 2 Outline Block ciphers P1 P2 P3 • Block ciphers/stream ciphers • Hash functions/MAC algorithms block block block • Modes of operation and authenticated cipher cipher cipher encryption • How to encrypt/sign using RSA C1 C2 C3 • Multi-party computation • larger data units: 64…128 bits •memoryless • Concluding remarks • repeat simple operation (round) many times 3 3-DES: NIST Spec. Pub. 800-67 AES (2001) (May 2004) S S S S S S S S S S S S S S S S • Single DES abandoned round • two-key triple DES: until 2009 (80 bit security) • three-key triple DES: until 2030 (100 bit security) round MixColumnsS S S S MixColumnsS S S S MixColumnsS S S S MixColumnsS S S S hedule Highly vulnerable to a c round • Block length: 128 bits related key attack • Key length: 128-192-256 . Key S Key . bits round A $ 10M machine that cracks a DES Clear DES DES-1 DES %^C& key in 1 second would take 149 trillion text @&^( years to crack a 128-bit key 1 23 1 New Developments in Cryptography March 2012 Bart Preneel AES variants (2001) AES implementations: • AES-128 • AES-192 • AES-256 efficient/compact • 10 rounds • 12 rounds • 14 rounds • sensitive • classified • secret and top • NIST validation list: 1953 implementations (2008: 879) secret plaintext plaintext plaintext http://csrc.nist.gov/groups/STM/cavp/documents/aes/aesval.html round round. -
Introduction
CS 127: Cryptography / Boaz Barak Lecture 1 - Introduction Optional additional reading: Chapters 1 and 2 of Katz-Lindell book.1 Ever since people started to communicate, there were some messages that they wanted kept secret. Thus cryptography has an old though arguably undistin- guished history. For a long time cryptography shared similar features with Alchemy as a domain in which many otherwise smart people would be drawn into making fatal mistakes. d The definitive text on the history of cryptography is David Kahn’s “The Codebreakers”, whose title already hints at the ultimate fate of most cryptosystems.2 (See also “The Code Book” by Simon Singh.) We now recount just a few stories to get a feel for this field. But, before we do so, we should introduce the cast of characters. The basic setting of “encryption” or “secret writing” is the following: one person, whom we will call Alice, wishes to send another person, whom we will call Bob, a secret message. Since Alice and Bob are not in the same room (perhaps because Alice is imprisoned in a castle by her cousin the queen of England), they cannot communicate directly and need to send their message in writing. Alas, there is a third person, whom we will call Eve, that can see their message. Therefore Alice needs to find a way to encode or encrypt the message so that only Bob (and not Eve) will be able to understand it. In 1587, Mary the queen of Scots, and the heir to the throne of England, wanted to arrange the assasination of her cousin, queen Elisabeth I of England, so that she could ascend to the throne and finally escape the house arrest under which she has been for the last 18 years. -
Saville Free
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Cryptology: an Historical Introduction DRAFT
Cryptology: An Historical Introduction DRAFT Jim Sauerberg February 5, 2013 2 Copyright 2013 All rights reserved Jim Sauerberg Saint Mary's College Contents List of Figures 8 1 Caesar Ciphers 9 1.1 Saint Cyr Slide . 12 1.2 Running Down the Alphabet . 14 1.3 Frequency Analysis . 15 1.4 Linquist's Method . 20 1.5 Summary . 22 1.6 Topics and Techniques . 22 1.7 Exercises . 23 2 Cryptologic Terms 29 3 The Introduction of Numbers 31 3.1 The Remainder Operator . 33 3.2 Modular Arithmetic . 38 3.3 Decimation Ciphers . 40 3.4 Deciphering Decimation Ciphers . 42 3.5 Multiplication vs. Addition . 44 3.6 Koblitz's Kid-RSA and Public Key Codes . 44 3.7 Summary . 48 3.8 Topics and Techniques . 48 3.9 Exercises . 49 4 The Euclidean Algorithm 55 4.1 Linear Ciphers . 55 4.2 GCD's and the Euclidean Algorithm . 56 4.3 Multiplicative Inverses . 59 4.4 Deciphering Decimation and Linear Ciphers . 63 4.5 Breaking Decimation and Linear Ciphers . 65 4.6 Summary . 67 4.7 Topics and Techniques . 67 4.8 Exercises . 68 3 4 CONTENTS 5 Monoalphabetic Ciphers 71 5.1 Keyword Ciphers . 72 5.2 Keyword Mixed Ciphers . 73 5.3 Keyword Transposed Ciphers . 74 5.4 Interrupted Keyword Ciphers . 75 5.5 Frequency Counts and Exhaustion . 76 5.6 Basic Letter Characteristics . 77 5.7 Aristocrats . 78 5.8 Summary . 80 5.9 Topics and Techniques . 81 5.10 Exercises . 81 6 Decrypting Monoalphabetic Ciphers 89 6.1 Letter Interactions . 90 6.2 Decrypting Monoalphabetic Ciphers .