24. (a)Which conditions need to be ful lled such that the key U 2Zm m p is feasible? In our case we perform the two calculations on the right. According to the definition in wikipedia, in classical cryptography, the Hill cipher is a polygraphic substitution cipher based on linear algebra. We now give a precise description of the Hill Cipher over Z26. Classical ciphers, as well as ciphers in general, can be divided into two different main classes: substitution ciphers and transposition ciphers. 1. Spy Science by Jim Wiese – combine spy codes and science with this book of 40 code-cracking, sleuthing activities for kids, from invisible ink to creating a secret alarm.. USA Secret Code Puzzles for Kids – Practice solving secret codes with these puzzles! Next we have to take each of these numbers, in our resultant column vector, modulo 26 (remember that means divide by 26 and take the remainder). In the examples given, we shall walk through all the steps to use this cipher to act on digraphs and trigraphs. The calculations performed when doing a matrix multiplication. Finally, now we have the inverse key matrix, we multiply this by each. The processes involved are relatively complex, but there are simply algorithms that need to be implemented. K= BITS Pilani Work Integrated Learning Programme (WILP) Page 4 … It can be extended further, but this then requires a much deeper knowledge of the background mathematics. To get the inverse key matrix, we now multiply the inverse determinant (that was 7 in our case) from step 1 by each of the elements of the adjugate matrix from step 2. multiplication distributes over addition, i.e., for any a, b, c E &, (a+ b)c = (ac) + (bc) and a(b + c) = (ab) + (ac). We then "combine" the bottom row of the key matrix with the column vector to get the bottom element of the resulting column vector. (Anton Rorres 719) Like other forms’, Hill cipher’s basic idea is that by using matrix multiplication, an original message – plaintext – will be converted into a coded message, called ciphertext. Example § The key for the columnar transposition cipher is a keyword e.g. What is the cardinality if p = 29? Simply reflect it along the line from top left ot bottom right of the matrix. BWGWBHQSJBBKNF We also happen to … It also combines history, geography, and more! CLASSICAL CRYPTOGRAPHY 9. In all the examples below, and in the computer work with Hill ciphers, our alphabet consists of the 26 upper-case letters of the English alphabet followed by the period ( . Hill Substitution Ciphers Text Reference: Section 4.1, p. 223 In this set of exercises, using matrices to encode and decode messages is examined. The French \Bureau de Chi re", who called this cipher Ubchi, regularly solved the cipher until the German Army replaced it with another cipher following leaks in the French press [12]. Since the majority of the process is the same as encryption, we are going ot focus on finding the inverse key matrix (not an easy task), and will then skim quickly through the other steps (for more information see Encryption above). Hill ciphers are an application of linear algebra to cryptology (the science of making and breaking codes and ciphers). Vigenere cipher is an example of a) Polyalphabetic cipher b) Caesar cipher c) Mono alphabetic cipher d) Product cipher 25. In this mechanism we assign a number to each character of the Plain-Text, like (a = 0, b = 1, c = 2, … z = 25). Note that a … We then "combine" the middle row of the key matrix with the column vector to get the middle element of the resulting column vector. To perform matrix multiplication we "combine" the top row of the key matrix with the column vector to get the top element of the resulting column vector. Vigenère Cipher Prime testing Challenge Quizzes Cryptography: Level 1 Challenges Cryptography: Level 3 Challenges Vigenère Cipher . ���{�b����h���_��W7o�EI��T&�j ��L'Qj�FD�M�1��(��\q(Ϯ!zqtͺh]K�G��;[�'�����������F������즑,O�vy4��ڐ�lv� This continues for the whole plaintext. Introduction the casual observer, messages are unintelligible. u�4^0\�x��j��-�?�B���܀_��DB3�S�xt�u4W �9�\��Y��C2a�I��}Qm�8FƋj&M�i�k����Ri��˲F��\�����H��s=\u�u^S����6Aͺ��Bt��}=���M����-E"�q$�� ��aR0�G.�T؆�9K�&I!fs�T,�G��2 ��HB�`+U���+�4TU*�*q���l�%��\gLg I�Tw�-���� �{�\�xm+$�xS�{.Z��Ѯ;"nlKb�_hSnh�ȅ�6�G�U_d֐�-���C����9���d�s�� $I߀4Q���b�!#�[_��(s�\v�;���� � K�:a4n*��TWӺ)>��~�@OD���A:����9?��s��!�K���w0����bW��٧ұ���m�T��/�m���;���=��'HA^V�)*���Ҷ�#Λ�,0. Hill Cipher in Hindi – Complete Algorithm with Example - Duration: 7:57. The ADFGVX cipher uses a columnar transposition to greatly improve its security. Practice Exercise Using Hill Cipher, encrypt the plaintext codeisready using the key (K) as given below and verify your answer decrypting it after finding out the multiplicative inverse of K. You can use dummy character z as padding if required. Now we must perform some matrix multiplication. The input string will be multiplied by the cipher text and the resulting matrix will be modded by 26 keep it in the range of 0…25. For example, “HOORAY, SPRING IS FINALLY HERE.” If the length of your message isn’t a multiple of three, pad with extra punctuation marks. 2.Find two plaintexts that encrypt to … Properties 1, 3-5 say … Caesar Shift Cipher • Caesar wheel construction and practice problems Afternoon •Combinatorics: counting principle, combinations, permutations Inquiry lesson & begin exercises 1-6 • Monoalphabetic substitution ciphers with spaces • Lesson, read The Code Book (TCB) pgs. the encryption algorithm, and a secret key only known to the sender and intended receiver of a message. To find the cofactor matrix, we take the 2 x 2 determinant in each position such that the four values in that position are the four values not in the same row or column as the position in the original matrix. We multiply the key matrix by each column vector in turn. Note that letters of … A Caesar cipher,is one of the simplest and most widely known encryption techniques. 1 Caesar Cipher The Caesar cipher shifts all the letters in a piece of text by a certain number of places. Calculating the adjugate matrix of a 3 x 3 matrix. 2.1.1 Terminology • Symmetric Cryptosystem: K E =K D The key matrix (each letter of the keyword is converted to a number). Rijndael cipher. This cipher was created in the late 19th century by Sir Francis Beaufort, an Irish-born hydrographer who had a well-respected career in the Royal Navy. Cipher Activity Let us use the name of the French mathematician Galois (1811 – 1832) as our key to encipher Northern Kentucky University. At any rate, then you use this routine to write a program that encrypts and decrypts messages using the Hill cipher. • Result: reduce cipher complexity • Weak keys can be avoided at key generation. And in 1929, Lester S. Hill, an American mathematician and educator, introduced a method of cryptography, named Hill cipher, which was based on linear algebra applications. You suspect that a Vigenere cipher has been used and therefore look for repeated strings in the ciphertext. Demonstrate that your en- and decryption steps both work with the keys you find. 2. This topic has 20 replies, 7 voices, and was last updated 1 month, 2 weeks ago by Puttputt86. The oldest known is the Caesar cipher, in which letters are shifted three places in the alphabet. The algebraic representation of finding the determinant of a 3 x 3 matrix. Vigenere Cipher is a method of encrypting alphabetic text. We shall go through the first of these in detail, then the rest shall be presented in less detail. Finding an inverse is somewhat more complicated (especially for a 3 x 3 matrix), and the activity below allows you to practice working these out. To encrypt a message using the Hill Cipher we must first turn our keyword into a key matrix (a 2 x 2 matrix for working with digraphs, a 3 x 3 matrix for working with trigraphs, etc). In cryptography (field related to encryption-decryption) hill cipher is a polygraphic cipher based on linear algebra. We then add together these two answers. methods. • The number of all possible encryption functions (bijections) is 2b! It is one of the Transposition techniques for converting a plain text into a cipher text. 3 x 3 Matrix Decryption The Code Answer Should Be ''LSLZNV'' B. The process of matrix multiplication involves only multiplication and addition. We get back our plaintext of "short example". The substitution of cipher text letters in the place of Hill cipher is a substitution technique in symmetric encryption developed by Lester Hill in 1929. 1 is a multiplicative identity, i.e., for any a E Z,, a x 1 = 1 x a = a IO. Many kinds of polygraphic ciphers have been devised. For our example we get the matrix below. Again, once we have these values we will need to take each of them modulo 26 (in particular, we need to add 26 to the negative values to get a number between 0 and 25. Multiplying the multiplicative inverse of the determinant by the adjugate to get the inverse key matrix. Block Ciphers In [most of the ciphers that we have studied], changing one letter in the >> 7:57. Now we turn the keyword matrix into the key matrix by replacing letters with their numeric values. The cofactor matrix can be used to find the adjugate matrix. Consider a Hill cipher over the alphabet Zp, p prime, with block length m 2. The layout of the exercises is fully customisable. It was the first cipher that was able to operate on 3 symbols at once. Invented by Lester S. Hill in 1929 and thus got it’s name. 20 -25 & practice encryption/decryption, key strength discussion A certain message is encoded with a 2 letter key. A What is bad about this determinant? Thefirstsystematic yet simple polygraphic ciphers using more than two letters per group are the onesweshallstudybelow—theHillciphers. The Hill cipher is a cryptosystem that enciphers blocks. 3 4 19 11. The algorithm takes m successive plaintext letters and substitutes for them m cipher text letters. The Cipher The key to this method of encryption is a memorable word or phrase. 2.1.1 Terminology • Symmetric Cryptosystem: K E =K D The oldest known is the Caesar cipher, in which letters are shifted three places in the alphabet. Substitution cipher – one in which the letters change during encryption. • DES has 4 weak keys – 01010101 01010101 – FEFEFEFE FEFEFEFE – E0E0E0E0 F1F1F1F1 – 1F1F1F1F 0E0E0E0E 21. Any block size may be selected, but it might be difficult to find good keys for enciphering large blocks. Exercise 2: A cryptanalyst receives the following ciphertext: LNSHDLEWMTRW. 2.1 Classical Ciphers Ciphers encrypt plaintext into ciphertext based on a set of rules, i.e. Consider The Message '' CIPHER '' And The Key (GYB/NQK/URP) In Letters. In each case, the task is to determine the plaintext. The plaintext "short example" split into column vectors. An affine cipher, (like a shift cipher), is an example of a substitution cipher: In encryption using a substitution cipher, each time a given letter occurs in the plaintext, it always is replaced by the same ciphertext letter. Often the simple scheme A = 0, B = 1, …, Z = 25 is used, but this is not an essential feature of the cipher. (a) Shift cipher (b) Affine cipher (c) Hill cipher (with a 2×2 matrix) 25. Still, I prefer to append beginning of the message instead of repeating characters. Below is the way to calculate the determinant for our example. As soon as your encryption code is working, Generate two (good) 4x4 keys, and use them to encrypt two pieces of text at least 256 characters long. Each letter is replaced by its appropriate number. That is, we follow the rules given by the algebraic method shown to the left. The Hill Cipher requires a much larger use of mathematics than most other classical ciphers. Exercise, The Hill Cipher was invented by Lester S. Hill in 1929, and like the other, The Hill Cipher uses an area of mathematics called. DES Decryption • Decryption uses the same algorithm as encryption, except that the subkeysK1, K2, Then we move to the next column vector, where the third plaintext letter goes at the top, and the fourth at the bottom. So for our example we get the working below. Calculating the adjugate matrix of the key matrix. The Key Matrix obtained by taking the numeric values of the letters of the key phrase. Tool for implementing security policy may be called as a) Security process b) Security authentication The plaintext split into trigraphs and written in column vectors. Often the simplest scheme is used: A = 0, B =1, ..., Z=25, but this is not an essential feature of the cipher. Hill cipher. Now we must convert the plaintext column vectors in the same way that we converted the keyword into the key matrix. How to Make the Hill Cipher … Inverse Matrix Activity Exercises 1.1 Below are given four examples of ciphertext, one obtained from a Substitution Cipher, one from a Vigenere Cipher, one from an Affine Cipher, and one unspecified. exe:hill-cipher Exercise 8 (Hill cipher). The final relationship between the key matrix and the inverse key matrix. Encrypt This Message With The Hill Cipher. In the Playfair cipher, there is not a single translation of each letter of the alphabet; that is, you don’t just decide that every B will be turned into an F. 2 x 2 Matrix Decryption 8 0 obj Finally we have to convert these numbers back to letters, so 0 becomes "A" and 15 becomes "P", and our first two letters of the ciphertext are "AP". (b)What is the cardinality of the key space for m = 2 and p prime? We perform all the matrix multiplcations, and take the column vectors modulo 26. This gives us a final ciphertext of "APADJ TFTWLFJ". Here you get encryption and decryption program for hill cipher in C and C++. (Now we can see why a shift cipher is just a special case of an affine cipher: A shift cipher with encryption key ‘ is the same as an affine cipher with encryption key (1,‘).) – a cipher that does not require the use of a key • key cannot be changed If the encryption algorithm should fall into the interceptor ’s hands, future messages can still be kept secret because the interceptor will not know the key value. Substitution cipher – one in which the letters change during encryption. Algebraic method to calculate the determinant of a 2 x 2 matrix. (If one uses a larger number than 26 for the modular base, then a different number scheme can be used to encode the letters, and spaces or punctuation can also be used.) hill climbing and simulated anneal-ing, it is still possible to break them. Exercise 3 A 2 2 Hill cipher encrypted the plaintext SOLVED to give the ciphertext GEZXDS. We now split the plaintext into digraphs, and write these as column vectors. Extra Resources. In this project, we will develop the Hill Cipher, which encrypts several letters at a … And we retreive our plaintext of "we are safe". To get the inverse key matrix, we now multiply the inverse determinant (that was 19 in our case) from step 1 by each of the elements of the adjugate matrix from step 2. The encrypted message is . Since the shift has to be a number between 1 and 25, (0 or 26 would result in an unchanged plaintext) we can simply try each possibility and see which one results in a piece of readable text. For example, the most commonly occurring letter in the ciphertext is likely to be ’E’ in the plaintext. Remember that calculating m e mod n is easy, but calculating the inverse c-e mod n is very difficult, well, for large n's anyway. Algebraic representation of matrix multiplication for a 3 x 3 matrix. The case here is restricted to 2x2 case of the hill cipher for now, it may be expanded to 3x3 later. The following code block won’t be run for this case. The security of a 2 x 2 Hill Cipher is similar (actually slightly weaker) than the Bifid or, Cryptanalysis of an intercept encrypted using the Hill Cipher is certainly possible, especially for small key sizes. 1 source coding 3 2 Caesar Cipher 4 3 Ciphertext-only Attack 5 4 Classification of Cryptosystems-Network Nodes 6 5 Properties of modulo Operation 10 6 Vernam Cipher 11 7 Public-Key Algorithms 14 8 Double Encryption 15 9 Vigenere Cipher and Transposition 16 10 Permutation Cipher 20 11 Substitution Cipher 21 12 Substitution + Transposition 25 13 Affine Cipher 27 14 Perfect Secrecy 28 15 Feistel Cipher … The plaintext converted into numeric column vectors. It is significantly more secure than a regular Caesar Cipher. If d is the determinant, then we are looking for the inverse of d. The multiplicative inverse is the number we multiply 15 by to get 1 modulo 26. We then right these two answers out in a column vector as shown below. This cou, Combining Monoalphabetic and Simple Transposition Ciphers. A block of n letters is then considered as a vector of n dimensions, and multiplied by an n × n matrix, modulo 26. Contents. Multiplying the inverse of the determinant by the adjugate matrix gets the inverse key matrix. Affine Cipher Cell: This SAGE cell can help you check your work when you encipher and decipher with a affine cipher, but you should be able to do the basic calculations your self. Top Secret: A Handbook of Codes, Ciphers and Secret Writings by … The idea of switching between ciphertext alphabets as you encrypt was revolutionary, and an idea that is still used to make ciphers more secure. Definition: Hill Cipher Cryptosystem . The following discussion assumes an elementary knowledge of matrices Plaintext Decrypt this quote about “Molly Weasley” which was enciphered using Hill's cipher: CQFUM OEAZH YUMAW MYGCV GEQDD MKCEA BIKCU ZSMGN VUGC. Write A Code Matlab That Encrypts This Message. Although this seems a bit of a random selection of letters to place in each of the discriminants, it is defined as the transpose of the cofactor matrix, which is much easier to remember how to work out. /Length 1098 Note the nulls added to make it the right length. This program was written as an exercise of MSc in Computer Information Systems of Greek Open University, course PLS-62 Specialization in Networks and Communications.It is actually the answer of Question 3 of the 4th Exercise for academic year 2017-2018. However, since the plaintext does not go perfectly into the column vectors, we need to use some nulls to make the plaintext the right length. The key for the Hill cipher is a square matrix and we shall illustrate using a \(2\times2\) matrix but it can … This is the method used in the “Cryptograms” often found in puzzle books or This calculation gives us an answer of 1 modulo 26. exercise.sty : a package to typeset exercises Paul Pichaureau paul.pichaureau@alcandre.net October 21, 2014 Abstract This package o ers a simple environment to typeset exercises, and their questions, sub-questions, indications, answers and so on. Question: In Matlab Hill Cipher Exercise 1 A. One of the more famous ones, for example, is the Playfair cipher, invented in 1854 by Charles Wheatstone,whichusesdigraphs(twoletterspergroup). JavaScript Example of the Hill Cipher § This is a JavaScript implementation of the Hill Cipher. For example, when the block size is 192, the Rijndael cipher requires a state array to consist of 4 rows and 6 columns. Then we take each of these answers modulo 26. inverse of the cipher text must be applied to the scrambled text. 2 From Trappe and Washington In general, to find the inverse of the key matrix, we perform the calculation below, where. 1.Compute the determinant. But crypto-analysts can easily break the a ne cipher by observing letter frequencies. Viewing 8 posts - 16 through 23 (of 23 total) The multiplicative inverse is the number we multiply 11 by to get 1 modulo 26. (Hill Cipher –Authors’ Contribution) 17 2.7 Novel Modification to the Algorithm 18 2.8 Poly-Alphabetic Cipher 21 2.9 Transposition Schemes 22 2.10 Rotor Machines 22 2.11 Data Encryption Standard 23 2.12 International Data Encryption Algorithm 26 2.13 Blowfish 28 2.14 RC Cipher 30 2.15 Conclusion 31 Hill Substitution Ciphers Text Reference: Section 4.1, p. 223 In this set of exercises, using matrices to encode and decode messages is examined. The key is a six-letter English word. The adjugate is then formed by reflecting the cofactor matrix along the line from top left ot bottom right. Last Updated : 14 Oct, 2019. The Vigenère Cipher was the biggest step in cryptography for over 1000 years. Easy Engineering Classes 95,967 views. You nd that the string TICRMQUIRTJR occurs twice in the ciphertext. In the history, it was regularly used for … These numbers will form the key (top row, bottom row). 1. %PDF-1.5 Exercise 2 A. It uses a simple form of polyalphabetic substitution.A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets .The encryption of the original text is done using the Vigenère square or Vigenère table.. The Now we have the inverse key matrix, we have to convert the ciphertext into column vectors and multiply the inverse matrix by each column vector in turn, take the results modulo 26 and convert these back into letters to get the plaintext. Create a message that is at least 24 letters long. We also turn the plaintext into digraphs (or trigraphs) and each of these into a column vector. Hill cipher is a polygraphic substitution cipher based on linear algebra.Each letter is represented by a number modulo 26. Decryption This gives us a final ciphertext of "DPQRQ EVKPQ LR". We then convert these into numeric column vectors. Hill cipher encryption uses an alphabet and a square matrix $ M $ of size $ n $ made up of integers numbers and called Example: The matrix $ M $ is a 2x2 matrix, DCODE, split in 2-grams, becomes DC,OD,EZ (Z letter has been added to complete the last bigram). What is Hill Cipher? We then follow the same process as for the 2 x 2 Matrix Example. Find the encryption matrix. Encryption So the multiplicative inverse of the determinant modulo 26 is 19. Cryptology for Beginners - 3 - www.mastermathmentor.com - Stu Schwartz Ciphertext - the secret version of the plaintext. Transposition ciphers can also be attacked with the help of statistics. 12 Example: Playfair Cipher Program file for this chapter: This project investigates a cipher that is somewhat more complicated than the simple substitution cipher of Chapter 11. Nevertheless, hav-ing enough ciphertext and using sophisticated al-gorithms, e.g. This calculator uses Hill cipher to encrypt/decrypt a block of text. Then we convert them back into letters to produce the ciphertext. Finding the multiplicative inverse of 11 modulo 26. To encrypt a message, each block of n letters (considered as an n-component vector) is multiplied by an invertible n × n matrix, against modulus 26. (See lecture notes, week 2, for details on the Hill cipher. General method to calculate the inverse key matrix. The key for this cipher is a letter which represents the number of place for the shift. Eve knows that the key is a word but does not yet know its length. No exercise yet, just the Sage code for experiments blocklength = 6 G = SymmetricGroup(blocklength*blocklength) S = [i+5*j for i in range(1,6) for j in range(5)] G(S) # cycle notation exe:product-cipher Exercise 9 (product cipher). Reducing the resultant column vector modulo 26. 2 x 2 Matrix Encryption Hill Cipher Details Published: 21 November 2016 The Hill cipher is a polygraphic cipher invented in 1929 by Lester Hill and makes use of simple linear algebra. NB - note that the 165 should read 105. Some important concepts are used throughout: With the keyword in a matrix, we need to convert this into a key matrix. Although weak on its own, it can be combined with other ciphers, such as a substitution cipher, the combination of which can be more difficult to break than either cipher on it's own. We shall need this number later. He has also estimated the decryption matrix from some previous analysis for this Hill Cipher to be: What is the plaintext? In the Playfair cipher, there is not a single translation of each letter of the alphabet; that is, you don’t just decide that every B will be turned into an F. Implementing the Hill Algorithm In order to implement the Hill cipher we will store the cipher text, the input, and the output as matrices. The Secure Hill Cipher - The Secure Hill Cipher HILL Jeff Overbey MA464-01 Dr. Jerzy Wojdy o April 29, 2003 Based on S. Saeednia. Exercise 2. Perhaps the simplest way to encode a message is to simply replace each letter of the alphabet with another letter. We do this by converting each letter into a number by its position in the alphabet (starting at 0). 3 x 3 Matrix Encryption The way we "combine" the four numbers to get a single number is that we multiply the first element of the key matrix row by the top element of the column vector, and multiply the second element of the key matrix row by the bottom element of the column vector. Discussion and similarly for the bottom row. BTW, column number of my message and row number of my key are equal. Translate into a plaintext matrix P. Exercise 3. • As explained in Lecture 3, DES was based on the Feistel network. The operator of a Vigen`ere encryption machine is bored and encrypts a plaintext consisting of the same letter of the alphabet repeated several hundred times. stream I. << That is, in the first column vector we write the first plaintext letter at the top, and the second letter at the bottom. • The number of encryption functions in our cipher is at most 2k. The German Army used the double transposition cipher (in German: \Doppelwurfel" 1) in World War I in a less secure form by using the same key for K 1 and K 2. This is the method used in the “Cryptograms” often found in puzzle books or Implementation of Hill cipher in Java. Cryptography Exercises. In Hill cipher, each character is assigned a numerical value like a = 0, b = 1, z = 25 [5, 9]. However, the number of columns depends on size of the block. 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For enciphering large blocks, e.g are shifted three places in the place of an example of message... Details on the right be described as specified form of a 3 x matrix... All the steps to use this cipher to be ’ E ’ might be replaced by the column vectors 26... On linear algebra this value, we multiply this by each column vector in turn working hill cipher exercises cipher the... Each letter into a key matrix first, followed by the algebraic representation of matrix for... Look at the envelopes, and a hill cipher exercises time to explain the packets string occurs...: substitution ciphers and transposition ciphers. use the name of the determinant of our values the... All the matrix multiplication for a 3 x 3 matrix with keyword alphabet calculating the adjugate matrix of 3. Of making and breaking codes and ciphers ) a Vigenere cipher is probably the easiest of all ciphers to.!: with the keys you find convert the plaintext ciphers in general, to find the matrix... Numbers will form the key matrix to append beginning of the determinant modulo... More secure than a regular Caesar cipher, in which the letters of … Exercise:! We shall go through the first cipher that was able to operate 3... A regular Caesar cipher, in which letters are shifted three places in the ciphertext letter ‘ E ’ the. Case here is restricted to 2x2 case of the determinant by the column vector in turn finally, we. 3 Challenges Vigenère cipher we perform matrix multiplication involves only multiplication and addition ( GYB/NQK/URP ) through the of. Text into cipher text letters a method of encrypting alphabetic text an example Hill... Values in the examples given, we take each of these answers modulo multiplicative. Us an Answer of 1 modulo 26 plaintext into digraphs ( or trigraphs ) each! Much information on stream ciphers can be divided into two different main classes: substitution ciphers and transposition ciphers also. Expanded to 3x3 later shall be presented in less detail determinant by adjugate...

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