DOCSLIB.ORG

To Decode Short Cryptograms

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
To Decode Short Cryptograms To Decode Short Cryptograms George W. Hart hort cryptograms, in which an encoded sentence The solution of a cryptogram can either be given as an or quotation is to be decoded, are common pas- explicit sentence of plain text, or it can be characterized by times of many recreational puzzle enthusiasts. describing the permutation that was used to code the Here is a simple example of the type that can be plain text. This permutation can be inverted then to re- found in many collections of word games, and construct the plain text from the given cipher text. The daily in some newspapers: permutation used for this example codes each letter as the letter to its right on the standard typewriter keyboard GivenS (cipher text): YPNR,PTMPYYPNR:YJSYODYJRWlRDYOPM. (convenient for touch-typists), with the three letters on the Solution (plain text): TOBE,ORNOTTOBE:THAT I STHEQUESTION. extreme right, (P, L, and M) "wrapping around" to the left: A permutation of the 26-character alphabet is used to en- Plain: ABCDE FGH I JKLMNOPQRSTUVWXYZ code a sentence with spacing and punctuation intact. Cipher: SNVFRGH JOKLAZMPQWTDY I B E CUX Given only the encoded sentence (the "cipher text"), the Partial Permutation: SN**R* *JO .... MP*WTDYI ..... correct permutation is to be found so that the original sentence (the "plain text") can be understood. By framing An algorithm that decodes cryptograms must effec- the problem as a multiple-hypothesis detection problem, tively choose one of the 26! (~ 4 - 1026) different permuta- applying a maximum-likelihood criterion, using English tions according to some criterion. Actually, there are usu- language word frequency data, approximating liberally, ally somewhat fewer possibilities, because only a "partial and constructing a well-organized search tree, a rather permutation" is required. Only 12 distinct letters appear simple algorithm results, which quickly deciphers even in the preceding quote, so cipher entries for the plain let- difficult cryptograms. ters that do not appear may be left undefined, indicated Cryptograms of this form--simple permutation substi- here with an (asterisk) * tutions with word divisions--have been employed for message concealment, at least, since Roman times. The Criteria solution of simple permutation ciphers has not been of The first tool one might think of when constructing a se- much practical importance, since their use for military lection criterion is a probability distribution for the 26 let- communication was superseded in the nineteenth cen- ters. By tabulating the occurrences of each alphabetic tury, but they remain a formidable puzzle for those who character in large samples of text, one determines that the enjoy word games. Experienced solvers can manually most frequent letter is ~,, occurring about 13% of the time, solve a typical one-sentence cryptogram in a few minutes, while the least common is 7., with a frequency about 0.1%. but carefully constructed short puzzles, with unusual let- Complete rank orderings vary somewhat depending on ter frequencies or atypical letter combinations, can stymie the body of the text selected for tabulation. Four pub- even expert solvers. Many strategies are published for lished examples for modern English [2, 3, 9, 12] are: manual decipherment, e.g., [1-3, 5, 8-10, 12], but these ETAON I SRHLDCUP FMWY BGVKQXJ Z all require human pattern recognition skills "in the loop," ETNR I OASDHLCF PUM Y GWVBXKQ J Z and are not explicit enough to be called algorithms. This ETAO I NSRHLDCUM FWG Y P BVKX J QZ author is aware of only one previously published method ETOAN I RSHDLUCMP F YWG BVKJ XZQ for automatic solution--a relaxation method [7], also see [4]--but it is not suitable for short cryptograms. A natural solution criterion which can make use of a ~O2 September 1994/%1.37, No.9 ¢@IUlWUNICATIONS OP THN AClm given ordering is to select a permutation that results in a then f-l(Z). A probabilistic model for natural language hypothesized plain text with as close an ordering as possi- text assigns a probability P(S) to any string S. The ML ble to a standard published ordering. Variations on this criterion is then to chose the permutation idea appear in all discussions of cryptography. The exis- tence of conflicting nominal orderings, such as the pre- f = argmaxP(f - l(Z)). (1) ceding four is only a minor flaw with this approach; there f is a much more serious problem. While it is straightfor- There are two sizable problems: determining an appro- ward to construct a permutation that results in the desired priate probability distribution P for English sentences and letter ordering, the result of such an algorithm (the "out- choosing among the 26! values for the argumentf. put text") will, almost certainly, be gibberish for a short length of text. Figure 1 illustrates such an algorithm, and Language Model why it fails. The fundamental problem is that short text It is not clear that the notion of a probability distribution fragments have sample statistics that differ considerably for English sentences makes any mathematical, linguistic, from one another and larger samples. Even large samples or philosophical sense. People do not decide what to say vary, as the four orderings above attest, so the use of letter or write by any procedure analogous to flipping coins. It is frequencies alone may fail even with texts as large as more correct to describe the following as a text model 10,000 letters. based on word frequencies. Similar arguments and examples can be constructed to Many tabulations of word frequencies have been un- show that simple modifications of this character-based dertaken. Here is one listing of the 135 top-ranked words probability distribution criterion also do not work in short of modern American English, starting with the most cryptograms. Putative methods might include the fre- common [6]: quencies of word-initial letters or word-final letters, or the joint statistics of pairs or triples of letters, using Markov THE OF AND TO A IN THAT IS WAS HE FOR IT WITH AS HIS ON BE AT models such as in [5, 8, 10]. However these considerations BY I THIS HAD NOT ARE BUT FROM OR HAVE AN THEY WHICH ONE only exacerbate the problems, since only a very small frac- YOU WERE HER ALL SHE THERE WOULD THEIR WE HIM BEEN HAS tion of the possible n-tuples appears. The fundamental WHEN WHO WILL MORE NO IF OUT SO SAID WHAT UP ITS ABOUT problem remains that there is a large variance to the sam- INTOTHAN THEM CAN ONLYOTHER NEW SOMECOULD TIME THESE ple statistics of short segments of text. These measures can TWO MAY THEN DO FIRSTANY MY NOW SUCH LIKE OUR OVER MAN only be expected to converge when large samples of ci- ME EVEN MOST MADE AFTER ALSO DID MANY BEFORE MUST pher text are available. The method of [7] uses letter tri- THROUGH BACK YEARS WHERE MUCH YOUR WAY WELL DOWN ples, but based on the examples presented, it apparently SHOULD BECAUSE EACH JUST THOSE PEOPLE MR HOW TOO LIT- requires approximately 1,000 characters of text. To solve typical cryptograms containing only 5 to 25 words, a different tack is employed here, analogous to the method of Figure 1, but using complete words rather than Figure 1. A possible "message" which matches the letters. A word-based approach appears formidable at first known letter frequencies of English can always be because there are many more words in English than let- found by counting the occurrences of each cipher ters-over 100,000. However, it turns out that the use of a text letter and ranking them from most to least word table on the order of 100 to 1,000 entries allows for a frequent (1st two columns), then matching with a very effective method of solution. known ordering (ETAONISRHLDC... in 3rd column). As an appropriate criterion, a maximum-likelihood The output of this algorithm comes as close as pos- (ML) estimator is used, justified by the fact that it gives a sible to the correct letter frequencies of English, minimum probability of error under the assumption that but is gibberish. The problem is that typical sen- all permutations are equally likely [11]. Letf represent an tences of English do not display the actual statistics encoding permutation of the alphabet, applied to the of English because they are too short. In the plain-text string on a character-by-character basis. Let Z quoted line of Shakespeare, for example, "T" is the be the given cipher text. The corresponding plain text is most common letter (column 4), not "E." Given Cipher Text: YP NR, PT MPY YP NR: YJSY OD YJR WIRDYOPM. Cipher Number of chars, occurences Y E T P T O R A E N,M,J,O,D O,N,I,S,R B,N,H, I, S T,S,W,I H,L,D,C R,A,Q,U Resulting Output Text ET OA, TH NTE ET OA: EILE SR EIA DCARESTN. COMMUNI¢ATIONSOleTHIIACM September 1994/Vol.37, No.9 103 TLE STATE GOOD VERY MAKE WORLD STILL OWN SEE MEN WORK the most fundamental syntactic principles such as word LONG GET HERE BETWEEN BOTH LIFE BEING UNDER NEVER DAY order. But again the justification is in the results. SAME ANOTHER KNOW WHILE LAST (2) We can interpret (5) in two ways, according to how we count repeated words. When a given word appears k Surprisingly, although there are over 100,000 English times in a single sentence, we could include the corre- words, a randomly selected word of an English sentence sponding probability k times in the product (if we are has a greater than 50% chance of being found in, this list.
Load more

Recommended publications
  • Recommendation for Block Cipher Modes of Operation Methods
    NIST Special Publication 800-38A Recommendation for Block 2001 Edition Cipher Modes of Operation Methods and Techniques Morris Dworkin C O M P U T E R S E C U R I T Y ii C O M P U T E R S E C U R I T Y Computer Security Division Information Technology Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-8930 December 2001 U.S. Department of Commerce Donald L. Evans, Secretary Technology Administration Phillip J. Bond, Under Secretary of Commerce for Technology National Institute of Standards and Technology Arden L. Bement, Jr., Director iii Reports on Information Security Technology The Information Technology Laboratory (ITL) at the National Institute of Standards and Technology (NIST) promotes the U.S. economy and public welfare by providing technical leadership for the Nation’s measurement and standards infrastructure. ITL develops tests, test methods, reference data, proof of concept implementations, and technical analyses to advance the development and productive use of information technology. ITL’s responsibilities include the development of technical, physical, administrative, and management standards and guidelines for the cost-effective security and privacy of sensitive unclassified information in Federal computer systems. This Special Publication 800-series reports on ITL’s research, guidance, and outreach efforts in computer security, and its collaborative activities with industry, government, and academic organizations. Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose.
    [Show full text]
  • Polish Mathematicians Finding Patterns in Enigma Messages
    Fall 2006 Chris Christensen MAT/CSC 483 Machine Ciphers Polyalphabetic ciphers are good ways to destroy the usefulness of frequency analysis. Implementation can be a problem, however. The key to a polyalphabetic cipher specifies the order of the ciphers that will be used during encryption. Ideally there would be as many ciphers as there are letters in the plaintext message and the ordering of the ciphers would be random – an one-time pad. More commonly, some rotation among a small number of ciphers is prescribed. But, rotating among a small number of ciphers leads to a period, which a cryptanalyst can exploit. Rotating among a “large” number of ciphers might work, but that is hard to do by hand – there is a high probability of encryption errors. Maybe, a machine. During World War II, all the Allied and Axis countries used machine ciphers. The United States had SIGABA, Britain had TypeX, Japan had “Purple,” and Germany (and Italy) had Enigma. SIGABA http://en.wikipedia.org/wiki/SIGABA 1 A TypeX machine at Bletchley Park. 2 From the 1920s until the 1970s, cryptology was dominated by machine ciphers. What the machine ciphers typically did was provide a mechanical way to rotate among a large number of ciphers. The rotation was not random, but the large number of ciphers that were available could prevent depth from occurring within messages and (if the machines were used properly) among messages. We will examine Enigma, which was broken by Polish mathematicians in the 1930s and by the British during World War II. The Japanese Purple machine, which was used to transmit diplomatic messages, was broken by William Friedman’s cryptanalysts.
    [Show full text]
  • Index-Of-Coincidence.Pdf
    The Index of Coincidence William F. Friedman in the 1930s developed the index of coincidence. For a given text X, where X is the sequence of letters x1x2…xn, the index of coincidence IC(X) is defined to be the probability that two randomly selected letters in the ciphertext represent, the same plaintext symbol. For a given ciphertext of length n, let n0, n1, …, n25 be the respective letter counts of A, B, C, . , Z in the ciphertext. Then, the index of coincidence can be computed as 25 ni (ni −1) IC = ∑ i=0 n(n −1) We can also calculate this index for any language source. For some source of letters, let p be the probability of occurrence of the letter a, p be the probability of occurrence of a € b the letter b, and so on. Then the index of coincidence for this source is 25 2 Isource = pa pa + pb pb +…+ pz pz = ∑ pi i=0 We can interpret the index of coincidence as the probability of randomly selecting two identical letters from the source. To see why the index of coincidence gives us useful information, first€ note that the empirical probability of randomly selecting two identical letters from a large English plaintext is approximately 0.065. This implies that an (English) ciphertext having an index of coincidence I of approximately 0.065 is probably associated with a mono-alphabetic substitution cipher, since this statistic will not change if the letters are simply relabeled (which is the effect of encrypting with a simple substitution). The longer and more random a Vigenere cipher keyword is, the more evenly the letters are distributed throughout the ciphertext.
    [Show full text]
  • Secure Communications One Time Pad Cipher
    Cipher Machines & Cryptology © 2010 – D. Rijmenants http://users.telenet.be/d.rijmenants THE COMPLETE GUIDE TO SECURE COMMUNICATIONS WITH THE ONE TIME PAD CIPHER DIRK RIJMENANTS Abstract : This paper provides standard instructions on how to protect short text messages with one-time pad encryption. The encryption is performed with nothing more than a pencil and paper, but provides absolute message security. If properly applied, it is mathematically impossible for any eavesdropper to decrypt or break the message without the proper key. Keywords : cryptography, one-time pad, encryption, message security, conversion table, steganography, codebook, message verification code, covert communications, Jargon code, Morse cut numbers. version 012-2011 1 Contents Section Page I. Introduction 2 II. The One-time Pad 3 III. Message Preparation 4 IV. Encryption 5 V. Decryption 6 VI. The Optional Codebook 7 VII. Security Rules and Advice 8 VIII. Appendices 17 I. Introduction One-time pad encryption is a basic yet solid method to protect short text messages. This paper explains how to use one-time pads, how to set up secure one-time pad communications and how to deal with its various security issues. It is easy to learn to work with one-time pads, the system is transparent, and you do not need special equipment or any knowledge about cryptographic techniques or math. If properly used, the system provides truly unbreakable encryption and it will be impossible for any eavesdropper to decrypt or break one-time pad encrypted message by any type of cryptanalytic attack without the proper key, even with infinite computational power (see section VII.b) However, to ensure the security of the message, it is of paramount importance to carefully read and strictly follow the security rules and advice (see section VII).
    [Show full text]
  • John F. Byrne's Chaocipher Revealed
    John F. Byrne’s Chaocipher Revealed John F. Byrne’s Chaocipher Revealed: An Historical and Technical Appraisal MOSHE RUBIN1 Abstract Chaocipher is a method of encryption invented by John F. Byrne in 1918, who tried unsuccessfully to interest the US Signal Corp and Navy in his system. In 1953, Byrne presented Chaocipher-encrypted messages as a challenge in his autobiography Silent Years. Although numerous students of cryptanalysis attempted to solve the challenge messages over the years, none succeeded. For ninety years the Chaocipher algorithm was a closely guarded secret known only to a handful of persons. Following fruitful negotiations with the Byrne family during the period 2009-2010, the Chaocipher papers and materials have been donated to the National Cryptologic Museum in Ft. Meade, MD. This paper presents a comprehensive historical and technical evaluation of John F. Byrne and his Chaocipher system. Keywords ACA, American Cryptogram Association, block cipher encryption modes, Chaocipher, dynamic substitution, Greg Mellen, Herbert O. Yardley, John F. Byrne, National Cryptologic Museum, Parker Hitt, Silent Years, William F. Friedman 1 Introduction John Francis Byrne was born on 11 February 1880 in Dublin, Ireland. He was an intimate friend of James Joyce, the famous Irish writer and poet, studying together in Belvedere College and University College in Dublin. Joyce based the character named Cranly in Joyce’s A Portrait of the Artist as a Young Man on Byrne, used Byrne’s Dublin residence of 7 Eccles Street as the home of Leopold and Molly Bloom, the main characters in Joyce’s Ulysses, and made use of real-life anecdotes of himself and Byrne as the basis of stories in Ulysses.
    [Show full text]
  • 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.
    [Show full text]
  • Applications of Search Techniques to Cryptanalysis and the Construction of Cipher Components. James David Mclaughlin Submitted F
    Applications of search techniques to cryptanalysis and the construction of cipher components. James David McLaughlin Submitted for the degree of Doctor of Philosophy (PhD) University of York Department of Computer Science September 2012 2 Abstract In this dissertation, we investigate the ways in which search techniques, and in particular metaheuristic search techniques, can be used in cryptology. We address the design of simple cryptographic components (Boolean functions), before moving on to more complex entities (S-boxes). The emphasis then shifts from the construction of cryptographic arte- facts to the related area of cryptanalysis, in which we first derive non-linear approximations to S-boxes more powerful than the existing linear approximations, and then exploit these in cryptanalytic attacks against the ciphers DES and Serpent. Contents 1 Introduction. 11 1.1 The Structure of this Thesis . 12 2 A brief history of cryptography and cryptanalysis. 14 3 Literature review 20 3.1 Information on various types of block cipher, and a brief description of the Data Encryption Standard. 20 3.1.1 Feistel ciphers . 21 3.1.2 Other types of block cipher . 23 3.1.3 Confusion and diffusion . 24 3.2 Linear cryptanalysis. 26 3.2.1 The attack. 27 3.3 Differential cryptanalysis. 35 3.3.1 The attack. 39 3.3.2 Variants of the differential cryptanalytic attack . 44 3.4 Stream ciphers based on linear feedback shift registers . 48 3.5 A brief introduction to metaheuristics . 52 3.5.1 Hill-climbing . 55 3.5.2 Simulated annealing . 57 3.5.3 Memetic algorithms . 58 3.5.4 Ant algorithms .
    [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]
  • Algorithms and Mechanisms Historical Ciphers
    Algorithms and Mechanisms Cryptography is nothing more than a mathematical framework for discussing the implications of various paranoid delusions — Don Alvarez Historical Ciphers Non-standard hieroglyphics, 1900BC Atbash cipher (Old Testament, reversed Hebrew alphabet, 600BC) Caesar cipher: letter = letter + 3 ‘fish’ ‘ilvk’ rot13: Add 13/swap alphabet halves •Usenet convention used to hide possibly offensive jokes •Applying it twice restores the original text Substitution Ciphers Simple substitution cipher: a=p,b=m,c=f,... •Break via letter frequency analysis Polyalphabetic substitution cipher 1. a = p, b = m, c = f, ... 2. a = l, b = t, c = a, ... 3. a = f, b = x, c = p, ... •Break by decomposing into individual alphabets, then solve as simple substitution One-time Pad (1917) Message s e c r e t 18 5 3 17 5 19 OTP +15 8 1 12 19 5 7 13 4 3 24 24 g m d c x x OTP is unbreakable provided •Pad is never reused (VENONA) •Unpredictable random numbers are used (physical sources, e.g. radioactive decay) One-time Pad (ctd) Used by •Russian spies •The Washington-Moscow “hot line” •CIA covert operations Many snake oil algorithms claim unbreakability by claiming to be a OTP •Pseudo-OTPs give pseudo-security Cipher machines attempted to create approximations to OTPs, first mechanically, then electronically Cipher Machines (~1920) 1. Basic component = wired rotor •Simple substitution 2. Step the rotor after each letter •Polyalphabetic substitution, period = 26 Cipher Machines (ctd) 3. Chain multiple rotors Each rotor steps the next one when a full
    [Show full text]
  • Cryptanalysis of the ``Kindle'' Cipher
    Introduction PC1 Known-plaintext key-recovery Ciphertext only key-recovery Conclusion . Cryptanalysis of the “Kindle” Cipher Alex Biryukov, Gaëtan Leurent, Arnab Roy University of Luxembourg SAC 2012 A. Biryukov, G. Leurent, A. Roy (uni.lu) Cryptanalysis of the “Kindle” Cipher SAC 2012 1 / 22 Introduction PC1 Known-plaintext key-recovery Ciphertext only key-recovery Conclusion . Cryptography: theory and practice In theory In practice ▶ Random Oracle ▶ Algorithms ▶ ▶ Ideal Cipher AES ▶ SHA2 ▶ Perfect source of ▶ RSA randomness ▶ Modes of operation ▶ CBC ▶ OAEP ▶ ... ▶ . Random Number Generators ▶ Hardware RNG ▶ PRNG A. Biryukov, G. Leurent, A. Roy (uni.lu) Cryptanalysis of the “Kindle” Cipher SAC 2012 2 / 22 Introduction PC1 Known-plaintext key-recovery Ciphertext only key-recovery Conclusion . Cryptography in the real world Several examples of flaws in industrial cryptography: ▶ Bad random source ▶ SLL with 16bit entropy (Debian) ▶ ECDSA with fixed k (Sony) ▶ Bad key size ▶ RSA512 (TI) ▶ Export restrictions... ▶ Bad mode of operation ▶ CBCMAC with the RC4 streamcipher (Microsoft) ▶ TEA with DaviesMeyer (Microsoft) ▶ Bad (proprietary) algorithm ▶ A5/1 (GSM) ▶ CSS (DVD forum) ▶ Crypto1 (MIFARE/NXP) ▶ KeeLoq (Microchip) A. Biryukov, G. Leurent, A. Roy (uni.lu) Cryptanalysis of the “Kindle” Cipher SAC 2012 3 / 22 Introduction PC1 Known-plaintext key-recovery Ciphertext only key-recovery Conclusion . Amazon Kindle ▶ Ebook reader by Amazon ▶ Most popular ebook reader (≈ 50% share) ▶ 4 generations, 7 devices ▶ Software reader for 7 OS, plus cloud reader ▶ Several million devices sold ▶ Amazon sells more ebooks than paper books ▶ Uses crypto for DRM (Digital Rights Management) A. Biryukov, G. Leurent, A. Roy (uni.lu) Cryptanalysis of the “Kindle” Cipher SAC 2012 4 / 22 Introduction PC1 Known-plaintext key-recovery Ciphertext only key-recovery Conclusion .
    [Show full text]
  • Crypyto Documentation Release 0.2.0
    crypyto Documentation Release 0.2.0 Yan Orestes Aug 22, 2018 API Documentation 1 Getting Started 3 1.1 Dependencies...............................................3 1.2 Installing.................................................3 2 Ciphers 5 2.1 Polybius Square.............................................5 2.2 Atbash..................................................6 2.3 Caesar Cipher..............................................7 2.4 ROT13..................................................8 2.5 Affine Cipher...............................................9 2.6 Rail Fence Cipher............................................9 2.7 Keyword Cipher............................................. 10 2.8 Vigenère Cipher............................................. 11 2.9 Beaufort Cipher............................................. 12 2.10 Gronsfeld Cipher............................................. 13 3 Substitution Alphabets 15 3.1 Morse Code............................................... 15 3.2 Binary Translation............................................ 16 3.3 Pigpen Cipher.............................................. 16 3.4 Templar Cipher.............................................. 18 3.5 Betamaze Alphabet............................................ 19 Python Module Index 21 i ii crypyto Documentation, Release 0.2.0 crypyto is a Python package that provides a set of cryptographic tools with simple use to your applications. API Documentation 1 crypyto Documentation, Release 0.2.0 2 API Documentation CHAPTER 1 Getting Started These instructions
    [Show full text]
  • Hill Cipher Cryptanalysis a Known Plaintext Attack Means That We Know
    Fall 2019 Chris Christensen MAT/CSC 483 Section 9 Hill Cipher Cryptanalysis A known plaintext attack means that we know a bit of ciphertext and the corresponding plaintext – a crib. This is not an unusual situation. Often messages have stereotypical beginnings (e.g., to …, dear …) or stereotypical endings (e.g, stop) or sometimes it is possible (knowing the sender and receiver or knowing what is likely to be the content of the message) to guess a portion of a message. For a 22× Hill cipher, if we know two ciphertext digraphs and the corresponding plaintext digraphs, we can easily determine the key or the key inverse. 1 Example one: Assume that we know that the plaintext of our ciphertext message that begins WBVE is inma. We could either solve for the key or the key inverse; let’s solve for the key inverse. ef23 9 Because WB corresponds to in = , gh2 14 ef22 13 and because VE corresponds to ma = . gh51 These result in two sets of linear congruences modulo 26: 23ef+= 2 9 22ef+= 5 13 and 23gh+= 2 14 22gh+= 5 1 We solve the systems modulo 26 using Mathematica. In[5]:= Solve[23e+2f == 9 && 22e+5f == 13, {e, f}, Modulus -> 26] Out[5]= {{e->1,f->19}} In[6]:= Solve[23g+2h == 14 && 22g+5h == 1, {g, h}, Modulus -> 26] Out[6]= {{g->20,h->11}} 2 Example two: Ciphertext: FAGQQ ILABQ VLJCY QULAU STYTO JSDJJ PODFS ZNLUH KMOW We are assuming that this message was encrypted using a 22× Hill cipher and that we have a crib.
    [Show full text]