Decoding Running Key Ciphers

Total Page:16

File Type:pdf, Size:1020Kb

Decoding Running Key Ciphers Decoding Running Key Ciphers Sravana Reddy∗ Kevin Knight Department of Computer Science Information Sciences Institute The University of Chicago University of Southern California 1100 E. 58th Street 4676 Admiralty Way Chicago, IL 60637, USA Marina del Rey, CA 90292, USA [email protected] [email protected] Abstract Since we know that the plaintext and running key are both drawn from natural language, our objective There has been recent interest in the problem function for the solution plaintext under some lan- of decoding letter substitution ciphers using techniques inspired by natural language pro- guage model is: cessing. We consider a different type of classi- ˆ cal encoding scheme known as the running key P = arg max log Pr(P ) Pr(RP,C ) (1) cipher, and propose a search solution using P Gibbs sampling with a word language model. where the running key RP,C is the key that corre- We evaluate our method on synthetic cipher- sponds to plaintext P and ciphertext C. texts of different lengths, and find that it out- Note that if RP,C is a perfectly random sequence performs previous work that employs Viterbi of letters, this scheme is effectively a ‘one-time pad’, decoding with character-based models. which is provably unbreakable (Shannon, 1949). The knowledge that both the plaintext and the key 1 Introduction are natural language strings is important in breaking The running key cipher is an encoding scheme that a running key cipher. uses a secret key R that is typically a string of words, The letter-frequency distribution of running key usually taken from a book or other text that is agreed ciphertexts is notably flatter than than the plaintext upon by the sender and receiver. When sending a distribution, unlike substitution ciphers where the plaintext message P , the sender truncates R to the frequency profile remains unchanged, modulo letter length of the plaintext. The scheme also relies on substitutions. However, the ciphertext letter distri- a substitution function f, which is usually publicly bution is not uniform; there are peaks corresponding known, that maps a plaintext letter p and key letter to letters (like I) that are formed by high-frequency r to a unique ciphertext letter c. The most common plaintext/key pairs (like E and E). choice for f is the tabula recta, where c = (p + r) 2 Related Work mod 26 for letters in the English alphabet, with A = 0,B = 1, and so on. 2.1 Running Key Ciphers To encode a plaintext with a running key, the Bauer and Tate (2002) use letter n-grams (without spaces in the plaintext and the key are removed, and smoothing) up to order 6 to find the most probable for every 0 ≤ i < |P |, the ciphertext letter at posi- plaintext/key character pair at each position in the ci- tion i is computed to be Ci ← f(Pi,Ri). Figure 1 phertext. They test their method on 1000-character shows an example encoding using the tabula recta. ciphertexts produced from plaintexts and keys ex- For a given ciphertext and known f, the plaintext tracted from Project Gutenberg. Their accuracies uniquely determines the running key and vice versa. range from 28.9% to 33.5%, where accuracy is mea- ∗Research conducted while the author was visiting ISI. sured as the percentage of correctly decoded char- 80 Proceedings of the 50th Annual Meeting of the Association for Computational Linguistics, pages 80–84, Jeju, Republic of Korea, 8-14 July 2012. c 2012 Association for Computational Linguistics Figure 1: Example of a running key cipher. Note that key is truncated to the length of the plaintext. Plaintext – linguistics is fun, Running Key – colorless green ideas, tabula recta substitution where Ci ← (Pi + Ri) mod 26 Plaintext: LINGUISTICSISFUN Running Key: COLORLESSGREENID Ciphertext: NWYULTWLAIJMWSCQ acters. Such figures are too low to produce read- tion that the length of the key is known. If unknown, able plaintexts, especially if the decoded regions are the key length can be inferred using the Kasiski Test not contiguous. Griffing (2006) uses Viterbi decod- (Kasiski, 1863) which takes advantage of repeated ing and letter 6-grams to improve on the above re- plaintext/key character pairs. sult, achieving a median 87% accuracy over several 1000-character ciphertexts. A key shortcoming of 3 Solution with Gibbs Sampling this work is that it requires searching through about In this paper, we describe a search algorithm that 5 26 states at each position in the ciphertext. uses Gibbs Sampling to break a running key cipher. 2.2 Letter Substitution Ciphers 3.1 Choice of Language Model Previous work in decipherment of classical ciphers The main advantage of a sampling-based approach has mainly focused on letter substitution. These ci- over Viterbi decoding is that it allows us to seam- phers use a substitution table as the secret key. The lessly use word-based language models. Lower or- ciphertext is generated by substituting each letter of der letter n-grams may fail to decipher most cipher- the plaintext according to the substitution table. The texts even with perfect search, since an incorrect table may be homophonic; that is, a single plaintext plaintext and key could have higher likelihood un- letter could map to more than one possible cipher- der a weak language model than the actual message. text letter. Just as in running key ciphers, spaces in the plaintext are usually removed before encoding. 3.2 Blocked Sampling Proposed decipherment solutions for letter substi- One possible approach is to sample a plaintext letter tution ciphers include techniques that use expecta- at each position in the ciphertext. The limitation of tion maximization (Ravi and Knight, 2008), genetic such a sampler for the running key problem is that algorithms (Oranchak, 2008), integer programming is extremely slow to mix, especially for longer ci- (Ravi and Knight, 2009), A* decoding (Corlett and phertexts: we found that in practice, it does not usu- Penn, 2010), and Bayesian learning with Dirichlet ally converge to the optimal solution in a reasonable processes (Ravi and Knight, 2011). number of iterations even with simulated annealing. We therefore propose a blocked sampling algorithm 2.3 Vigenere` Ciphers that samples words rather than letters in the plain- A scheme similar to the running key cipher is the Vi- text, as follows: genere` cipher, also known as the periodic key cipher. 1. Initialize randomly P := p p . p , fix R as Instead of a single long string spanning the length of 1 2 |C| the key that corresponds to P, C the plaintext, the key is a short string – usually but not always a single word or phrase – repeated to the 2. Repeat for some number of iterations length of the plaintext. Figure 2 shows an example Vigenere` cipher encoding. This cipher is less secure (a) Sample spaces (word boundaries) in P ac- than the running key, since the short length of the cording to Pr(P ) key vastly reduces the size of the search space, and (b) Sample spaces in R according to Pr(R) the periodic repetition of the key leaks information. (c) Sample each word in P according to Recent work on decoding periodic key ciphers Pr(P ) Pr(R), updating R along with P perform Viterbi search on the key using letter n- (d) Sample each word in R according to gram models (Olsen et al., 2011), with the assump- Pr(P ) Pr(R), updating P along with R 81 Figure 2: Example of a Vigenere` cipher cipher, with a 5-letter periodic key, repeated to the length of the plaintext. Plaintext – linguistics is fun, Periodic Key – green, tabula recta substitution. Plaintext: LINGUISTICSISFUN Running Key: GREENGREENGREENG Ciphertext: RZRKHOJXMPYZWJHT 3. Remove spaces and return P, R Corpus (Nelson and Kucera, 1979), with Kneser- Ney smoothing. We fixed the word language model Note that every time a word in P is sampled, it interpolation weight to λ = 0.7. induces a change in R that may not be a word or a sequence of words, and vice versa. Sampling word 4.2 Baseline and Evaluation boundaries will also produce hypotheses contain- ing non-words. For this reason, we use a word tri- For comparison with the previous work, we re- gram model linearly interpolated with letter trigrams implement Viterbi decoding over letter 6-grams (including the space character).1 The interpolation (Griffing, 2006) trained on the Brown Corpus. In mainly serves to smooth the search space, with the addition to decipherment accuracy, we compare the added benefit of accounting for out-of-vocabulary, running time in seconds of the two algorithms. misspelled, or truncated words in the actual plaintext Both decipherment programs were implemented in or key. Table 1 shows an example of one sampling Python and run on the same machines. The Gibbs iteration on the ciphertext shown in Figure 1. Sampler was run for 10000 iterations. As in the Griffing (2006) paper, since the plaintext and running key are interchangeable, we measure Table 1: First sampling iteration on the ciphertext NWYULTWLAIJMWSCQ the accuracy of a hypothesized solution against the reference as the max of the accuracy between the hy- Generate P, R P : WERGATERYBVIEDOW with letter trigrams R: RSHOLASUCHOESPOU pothesized plaintext and the reference plaintext, and Sample spaces in P P : WERGAT ER YB VIEDOW the hypothesized plaintext and the reference key. Sample spaces in R R: RS HOLASUCHOES POU Sample words in P P : ADJUST AN MY WILLOW 4.3 Results R: NT PATAWYOKNEL HOU Sample words in R P : NEWNXI ST HE SYLACT Table 2 shows the average decipherment accuracy of R: AS CHOLESTEROL SAX our algorithm and the baseline on each dataset.
Recommended publications
  • Download Download
    International Journal of Integrated Engineering: Special Issue 2018: Data Information Engineering, Vol. 10 No. 6 (2018) p. 183-192. © Penerbit UTHM DOI: https://doi.org/10.30880/ijie.2018.10.06.026 Analysis of Four Historical Ciphers Against Known Plaintext Frequency Statistical Attack Chuah Chai Wen1*, Vivegan A/L Samylingam2, Irfan Darmawan3, P.Siva Shamala A/P Palaniappan4, Cik Feresa Mohd. Foozy5, Sofia Najwa Ramli6, Janaka Alawatugoda7 1,2,4,5,6Information Security Interest Group (ISIG), Faculty Computer Science and Information Technology University Tun Hussein Onn Malaysia, Batu Pahat, Johor, Malaysia E-mail: [email protected], [email protected], {shamala, feresa, sofianajwa}@uthm.edu.my 3School of Industrial Engineering, Telkom University, 40257 Bandung, West Java, Indonesia 7Department of Computer Engineering, University of Peradeniya, Sri Lanka E-mail: [email protected] Received 28 June 2018; accepted 5August 2018, available online 24 August 2018 Abstract: The need of keeping information securely began thousands of years. The practice to keep the information securely is by scrambling the message into unreadable form namely ciphertext. This process is called encryption. Decryption is the reverse process of encryption. For the past, historical ciphers are used to perform encryption and decryption process. For example, the common historical ciphers are Hill cipher, Playfair cipher, Random Substitution cipher and Vigenère cipher. This research is carried out to examine and to analyse the security level of these four historical ciphers by using known plaintext frequency statistical attack. The result had shown that Playfair cipher and Hill cipher have better security compare with Vigenère cipher and Random Substitution cipher.
    [Show full text]
  • Codebusters Coaches Institute Notes
    BEING COVER AGENT FIXED DELAY, PILOT RIGHT PLANE, CATCH SMALL RADIO (CODEBUSTERS) This is the first year CodeBusters will be a National event. A few changes have been made since the North Carolina trial event last year. 1. The Atbash Cipher has been added. 2. The running key cipher has been removed. 3. K2 alphabets have been added in addition to K1 alphabets 4. Hill Cipher decryption has been added with a given decryption matrix. 5. The points scale has been doubled, but the timing bonus has been increased by only 50% in order to further balance the test. 1 TYPES OF PROBLEMS 1.1 ARISTOCRAT (EASY TO HARD DIFFICULTY) http://www.cryptograms.org/tutorial.php An Aristocrat is the typical Crypto-quote you see in the newspaper. Word spaces are preserved. No letter will stand for itself and the replacement table is given as a guide (but doesn’t need to be filled in by the team to get credit). FXP PGYAPYF FIKP ME JAKXPT AY FXP GTAYFMJTGF THE EASIEST TYPE OF CIPHER IS THE ARISTOCRAT A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Frequency 4 1 6 3 1 2 2 2 6 3 3 4 Replacement I F T A Y C P O E R H S 1.2 ARISTOCRATS WITH SPELLING AND/OR GRAMMAR ERRORS (MEDIUM TO VERY HARD DIFFICULTY) For these, either words will be misspelled or grammatical errors introduced. From a student perspective, it is what they might expect when someone finger fumbles a text message or has a bad voice transcription.
    [Show full text]
  • "Cyber Security" Activity
    Cyber Security Keeping your information safe Standards: (Core ideas related to the activity) NGSS: ETS1.B – A solution needs to be tested and them modified on the basis of the test results in order to improve it MS-PS4.C – Digitized signals sent as wave pulses are a more reliable way to encode and transmit information CC Math: 5.OA-3 – Analyze patterns and relationships K12CS: 3-5 CS-Devices – Computing devices may be connected to other devices or components to extend their capabilities. Connections can take many forms such as physical or wireless. 3-5 N&I-Cybersecurity – Information can be protected using various security measures. These measures can be physical or digital 3-5 IoC-Culture – The development and modification of computing technology is driven by people’s needs and wants and can affect different groups differently 6-8 CS-Devices – The interaction between humans and computing devices presents advantages, disadvantages, and unintended consequences. The study of human-computer interaction can improve the design of devices and extend the abilities of humans. 6-8 N&I-Cybersecurity – The information sent and received across networks can be protected from unauthorized access and modification in a variety of ways, such as encryption to maintain its confidentiality and restricted access to maintain its integrity. Security measures to safeguard online information proactively address the threat of breaches to personal and private data 6-8 A&P-Algorithms – Algorithms affect how people interact with computers and the way computers respond. People design algorithms that are generalizable to many situations 6-8 IoC-Culture – Advancements in computing technology change people’s everyday activities.
    [Show full text]
  • The Mathemathics of Secrets.Pdf
    THE MATHEMATICS OF SECRETS THE MATHEMATICS OF SECRETS CRYPTOGRAPHY FROM CAESAR CIPHERS TO DIGITAL ENCRYPTION JOSHUA HOLDEN PRINCETON UNIVERSITY PRESS PRINCETON AND OXFORD Copyright c 2017 by Princeton University Press Published by Princeton University Press, 41 William Street, Princeton, New Jersey 08540 In the United Kingdom: Princeton University Press, 6 Oxford Street, Woodstock, Oxfordshire OX20 1TR press.princeton.edu Jacket image courtesy of Shutterstock; design by Lorraine Betz Doneker All Rights Reserved Library of Congress Cataloging-in-Publication Data Names: Holden, Joshua, 1970– author. Title: The mathematics of secrets : cryptography from Caesar ciphers to digital encryption / Joshua Holden. Description: Princeton : Princeton University Press, [2017] | Includes bibliographical references and index. Identifiers: LCCN 2016014840 | ISBN 9780691141756 (hardcover : alk. paper) Subjects: LCSH: Cryptography—Mathematics. | Ciphers. | Computer security. Classification: LCC Z103 .H664 2017 | DDC 005.8/2—dc23 LC record available at https://lccn.loc.gov/2016014840 British Library Cataloging-in-Publication Data is available This book has been composed in Linux Libertine Printed on acid-free paper. ∞ Printed in the United States of America 13579108642 To Lana and Richard for their love and support CONTENTS Preface xi Acknowledgments xiii Introduction to Ciphers and Substitution 1 1.1 Alice and Bob and Carl and Julius: Terminology and Caesar Cipher 1 1.2 The Key to the Matter: Generalizing the Caesar Cipher 4 1.3 Multiplicative Ciphers 6
    [Show full text]
  • Substitution Ciphers
    Foundations of Computer Security Lecture 40: Substitution Ciphers Dr. Bill Young Department of Computer Sciences University of Texas at Austin Lecture 40: 1 Substitution Ciphers Substitution Ciphers A substitution cipher is one in which each symbol of the plaintext is exchanged for another symbol. If this is done uniformly this is called a monoalphabetic cipher or simple substitution cipher. If different substitutions are made depending on where in the plaintext the symbol occurs, this is called a polyalphabetic substitution. Lecture 40: 2 Substitution Ciphers Simple Substitution A simple substitution cipher is an injection (1-1 mapping) of the alphabet into itself or another alphabet. What is the key? A simple substitution is breakable; we could try all k! mappings from the plaintext to ciphertext alphabets. That’s usually not necessary. Redundancies in the plaintext (letter frequencies, digrams, etc.) are reflected in the ciphertext. Not all substitution ciphers are simple substitution ciphers. Lecture 40: 3 Substitution Ciphers Caesar Cipher The Caesar Cipher is a monoalphabetic cipher in which each letter is replaced in the encryption by another letter a fixed “distance” away in the alphabet. For example, A is replaced by C, B by D, ..., Y by A, Z by B, etc. What is the key? What is the size of the keyspace? Is the algorithm strong? Lecture 40: 4 Substitution Ciphers Vigen`ere Cipher The Vigen`ere Cipher is an example of a polyalphabetic cipher, sometimes called a running key cipher because the key is another text. Start with a key string: “monitors to go to the bathroom” and a plaintext to encrypt: “four score and seven years ago.” Align the two texts, possibly removing spaces: plaintext: fours corea ndsev enyea rsago key: monit orsto gotot hebat hroom ciphertext: rcizl qfkxo trlso lrzet yjoua Then use the letter pairs to look up an encryption in a table (called a Vigen`ere Tableau or tabula recta).
    [Show full text]
  • ISA 562 Information Security Theory & Practice
    ISA 562 Information Security Theory & Practice Introduction to Cryptography Agenda • Basics & Definitions • Classical Cryptography • Symmetric (Secret Key) Cryptography • DES (Data Encryption Standard) • Multiple Encryptions • Modes of Block Cipher Operations • Math Essential • Asymmetric (Public Key) Cryptography 2 1 Basics & Definitions Security Concepts (I) • Confidentiality – Prevent information from being exposed to unintended party – Ex: An employee should not come to know the salary of his manager • Integrity – Assure that the information has not been tempered – Ex: An employee should not be able to modify the employee's own salary • Identity – Assure that the party of concern is authentic - it is what it claims to be – Ex: An employee should be able to uniquely identify and authenticate himself/herself 4 2 Security Concepts (II) • Availability – Assure that unused service or resource is available to legitimate users – Ex: Paychecks should be printed on time as stipulated by law • Anonymity – Assure that the identity of some party is remain anonymous – Ex: The manager should not know who had a critical review of him • Non-Repudiation – Assure that authenticated party has indeed done something that cannot be denied – Ex: Once the employee has cashed his paycheck, he can’t deny it. 5 Cryptography • Crypt = secret • Graph = writing • Cryptography is the science / art of transforming meaningful information into unintelligible text Becoming a science that relies on mathematics (number theory, algebra) • Cryptanalysis is the science / art of breaking cryptographic codes • Cryptology is the science / art / study of both cryptography and cryptanalysis 6 3 Applications of Cryptography • Assuring document integrity • Assuring document confidentiality • Authenticating parties • Document signature • Non-repudiation • Secure transactions • Exchanging keys • Sharing Secrets • Digital cash • Preserving anonymity • Copyright protection • More .
    [Show full text]
  • A Complete Bibliography of Publications in Cryptologia
    A Complete Bibliography of Publications in Cryptologia Nelson H. F. Beebe University of Utah Department of Mathematics, 110 LCB 155 S 1400 E RM 233 Salt Lake City, UT 84112-0090 USA Tel: +1 801 581 5254 FAX: +1 801 581 4148 E-mail: [email protected], [email protected], [email protected] (Internet) WWW URL: http://www.math.utah.edu/~beebe/ 04 September 2021 Version 3.64 Title word cross-reference 10016-8810 [?, ?]. 1221 [?]. 125 [?]. 15.00/$23.60.0 [?]. 15th [?, ?]. 16th [?]. 17-18 [?]. 18 [?]. 180-4 [?]. 1812 [?]. 18th (t; m)[?]. (t; n)[?, ?]. $10.00 [?]. $12.00 [?, ?, ?, ?, ?]. 18th-Century [?]. 1930s [?]. [?]. 128 [?]. $139.99 [?]. $15.00 [?]. $16.95 1939 [?]. 1940 [?, ?]. 1940s [?]. 1941 [?]. [?]. $16.96 [?]. $18.95 [?]. $24.00 [?]. 1942 [?]. 1943 [?]. 1945 [?, ?, ?, ?, ?]. $24.00/$34 [?]. $24.95 [?, ?]. $26.95 [?]. 1946 [?, ?]. 1950s [?]. 1970s [?]. 1980s [?]. $29.95 [?]. $30.95 [?]. $39 [?]. $43.39 [?]. 1989 [?]. 19th [?, ?]. $45.00 [?]. $5.95 [?]. $54.00 [?]. $54.95 [?]. $54.99 [?]. $6.50 [?]. $6.95 [?]. $69.00 2 [?, ?]. 200/220 [?]. 2000 [?]. 2004 [?, ?]. [?]. $69.95 [?]. $75.00 [?]. $89.95 [?]. th 2008 [?]. 2009 [?]. 2011 [?]. 2013 [?, ?]. [?]. A [?]. A3 [?, ?]. χ [?]. H [?]. k [?, ?]. M 2014 [?]. 2017 [?]. 2019 [?]. 20755-6886 [?, ?]. M 3 [?]. n [?, ?, ?]. [?]. 209 [?, ?, ?, ?, ?, ?]. 20th [?]. 21 [?]. 22 [?]. 220 [?]. 24-Hour [?, ?, ?]. 25 [?, ?]. -Bit [?]. -out-of- [?, ?]. -tests [?]. 25.00/$39.30 [?]. 25.00/839.30 [?]. 25A1 [?]. 25B [?]. 26 [?, ?]. 28147 [?]. 28147-89 000 [?]. 01Q [?, ?]. [?]. 285 [?]. 294 [?]. 2in [?, ?]. 2nd [?, ?, ?, ?]. 1 [?, ?, ?, ?]. 1-4398-1763-4 [?]. 1/2in [?, ?]. 10 [?]. 100 [?]. 10011-4211 [?]. 3 [?, ?, ?, ?]. 3/4in [?, ?]. 30 [?]. 310 1 2 [?, ?, ?, ?, ?, ?, ?]. 312 [?]. 325 [?]. 3336 [?, ?, ?, ?, ?, ?]. affine [?]. [?]. 35 [?]. 36 [?]. 3rd [?]. Afluisterstation [?, ?]. After [?]. Aftermath [?]. Again [?, ?]. Against 4 [?]. 40 [?]. 44 [?]. 45 [?]. 45th [?]. 47 [?]. [?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?]. Age 4in [?, ?]. [?, ?]. Agencies [?]. Agency [?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?].
    [Show full text]
  • CS1132 Fall 2013 Assignment 2 Due 11/21 11:59Pm 1 Cryptography Fun!
    CS1132 Fall 2013 Assignment 2 due 11/21 11:59pm Adhere to the Code of Academic Integrity. You may discuss background issues and general strategies with others and seek help from course staff, but the implementations that you submit must be your own. In particular, you may discuss general ideas with others but you may not work out the detailed solutions with others. It is never OK for you to see or hear another student's code and it is never OK to copy code from published/Internet sources. If you feel that you cannot complete the assignment on you own, seek help from the course staff. When submitting your assignment, follow the instructions summarized in Section 4 of this document. Do not use the break or continue statement in any homework or test in CS1132. 1 Cryptography Fun! Just several decades ago, cryptography existed solely in the domain of national governments and large corporations. However, the advent of the Internet and the wide availability of computers have now made cryptography an indispensable part of everyday digital communications. In this part of the assignment, you will implement one well-known classical ciphers: the Vigenere cipher. This ci- phers predates modern cryptography but nonetheless provide a relevant and insightful look at some commonly used cryptography techniques. You will implement it as MATLAB functions that can be used to encrypt and subsequently decrypt messages. The Vigenre cipher is one of the most well-known ciphers of all time. It is a method of encrypting plaintext using a series of different Caesar ciphers based on the letters of the keyword.
    [Show full text]
  • Nomenclators Nomenclator Example Alberti's Cipher Disk
    Nomenclators Early code/cipher combination, popular form 1400s-1800s. Philip of Spain (1589, see Kahn): LO = Spain POM = King of Spain 64 = confederation overlined two-digit groups = null + substitution cipher with homophones Nomenclator Example Nomenclator used by Mary, Queen of Scots . in 1586 in the plot against Elizabeth I Taken from Simon Singh. The Code Book. Alberti’s Cipher Disk Invented by Leon Battista Alberti in 1460s. outer disk (fixed) plaintext inner disk (moving) ciphertext Agree on index letter on inner disk. Key: letter corresponding to index letter on outer disk. Key can change during encryption 1 Cipher Disk Examples Let’s choose “K” as index letter. Examples: rRVTZOK aKVtTRCK HKmZMEP Since the key can change, this cipher is no longer monoalphabetic, but polyalphabetic. Are there other ways to use the cipher disk? Johannes Trithemius 1462-1516, Germany Polygraphiae, 1518 First printed book on cryptography. • Ave Maria Cipher • Polyalphabetic substitution • Progressive key Steganographia, 1606 • hidden writing http://diglib.hab.de/drucke/12-3-rhet-2f/start.htm Polygraphiae I The Polygraphiae contains many pages of code. 2 Polygraphiae II: Ave Maria 1st and 2nd page Steganographia http://books.google.com/books?id=bQdC AAAAcAAJ&dq=Trithemius%20Stegano graphia&pg=PR6#v=onepage&q&f=false Polygraphiae III Tabula recta, from the 6th book of the Polygraphiae. • Polyalphabetic substitution • Progressive key The history of information security: a comprehensive handbook, de Leeuw, Bergstra 3 Polygraphiae IV Examples (starting with first alphabet) • Johannes • SUGKESUOWSUN The history of information security: a comprehensive handbook, de Leeuw, Bergstra Modern Tabula Recta More Examples (not from beginning) • XNNN • NUGUV http://commons.wikimedia.org/wiki/File:Vigenere-square.png Giovan Batista Belaso La cifra del.
    [Show full text]
  • Substitution Cipher in Cryptography, a Substitution Cipher Is a Method Of
    Substitution cipher In cryptography, a substitution cipher is a method of encryption by which units of plaintext are replaced with ciphertext according to a regular system; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by performing an inverse substitution. Substitution ciphers can be compared with transposition ciphers. In a transposition cipher, the units of the plaintext are rearranged in a different and usually quite complex order, but the units themselves are left unchanged. By contrast, in a substitution cipher, the units of the plaintext are retained in the same sequence in the ciphertext, but the units themselves are altered. There are a number of different types of substitution cipher. If the cipher operates on single letters, it is termed a simple substitution cipher; a cipher that operates on larger groups of letters is termed polygraphic. A monoalphabetic cipher uses fixed substitution over the entire message, whereas a polyalphabetic cipher uses a number of substitutions at different times in the message, where a unit from the plaintext is mapped to one of several possibilities in the ciphertext and vice-versa. Contents • 1 Simple substitution o 1.1 Examples o 1.2 Security for simple substitution ciphers • 2 Homophonic substitution • 3 Polyalphabetic substitution • 4 Polygraphic substitution • 5 Mechanical substitution ciphers • 6 The one-time pad • 7 Substitution in modern cryptography • 8 Substitution ciphers in popular culture Simple substitution 1 ROT13 is a Caesar cipher, a type of substitution cipher. In ROT13, the alphabet is rotated 13 steps.
    [Show full text]
  • Enhancing the Security of Simplified DES Algorithm Using Transposition and Shift Rows
    International Journal of Computer Science and Software Engineering (IJCSSE), Volume 6, Issue 5, May 2017 ISSN (Online): 2409-4285 www.IJCSSE.org Page: 115-119 Enhancing the Security of Simplified DES Algorithm Using Transposition and Shift Rows 1 2 3 Adeem Akhtar and Muhammad Zia Ullah Baig , Waleej haider 1, 2, 3 MS Computer Science, MAJU, Pakistan ABSTRACT Security is playing a very important and crucial role in the field of network communication system and Internet. 2. SIMPLIFIED DATA ENCRYPTION Simplified Data encryption standard (S-DES) is a private STANDARD key cryptography system that provides the security in communication system but now days the advancement in S-DES is a block cipher. It encrypts the data in a block the computational power the S-DES seems to be weak of 8 bit. It produces 8 bit cipher text. The key length is 10 bits. against the brute force attacks. To improve the security Initially the key is consisting of 10 bits. The algorithm is of S- DES algorithm the transposition and shift row shown in below figure1 [3]. techniques are added before the S-DES algorithm to perform its process. By using an Enhanced S-DES algorithm the security has been improved which is very crucial in the communication and field of Internet. If the transposition and shift row technique are used before the original S-DES algorithm then the intruder required first to break the original S-DES algorithm and then transposition and shift rows techniques. So the security is approximately double as compared to a simple S-DES algorithm.
    [Show full text]
  • Ministry of Defence Acronyms and Abbreviations
    Acronym Long Title 1ACC No. 1 Air Control Centre 1SL First Sea Lord 200D Second OOD 200W Second 00W 2C Second Customer 2C (CL) Second Customer (Core Leadership) 2C (PM) Second Customer (Pivotal Management) 2CMG Customer 2 Management Group 2IC Second in Command 2Lt Second Lieutenant 2nd PUS Second Permanent Under Secretary of State 2SL Second Sea Lord 2SL/CNH Second Sea Lord Commander in Chief Naval Home Command 3GL Third Generation Language 3IC Third in Command 3PL Third Party Logistics 3PN Third Party Nationals 4C Co‐operation Co‐ordination Communication Control 4GL Fourth Generation Language A&A Alteration & Addition A&A Approval and Authorisation A&AEW Avionics And Air Electronic Warfare A&E Assurance and Evaluations A&ER Ammunition and Explosives Regulations A&F Assessment and Feedback A&RP Activity & Resource Planning A&SD Arms and Service Director A/AS Advanced/Advanced Supplementary A/D conv Analogue/ Digital Conversion A/G Air‐to‐Ground A/G/A Air Ground Air A/R As Required A/S Anti‐Submarine A/S or AS Anti Submarine A/WST Avionic/Weapons, Systems Trainer A3*G Acquisition 3‐Star Group A3I Accelerated Architecture Acquisition Initiative A3P Advanced Avionics Architectures and Packaging AA Acceptance Authority AA Active Adjunct AA Administering Authority AA Administrative Assistant AA Air Adviser AA Air Attache AA Air‐to‐Air AA Alternative Assumption AA Anti‐Aircraft AA Application Administrator AA Area Administrator AA Australian Army AAA Anti‐Aircraft Artillery AAA Automatic Anti‐Aircraft AAAD Airborne Anti‐Armour Defence Acronym
    [Show full text]