Mod 26 cipher decoder. Linear Algebra for Cryptography 501 10.

Mod 26 cipher decoder dCode has a dedicated tool for this: convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc. Category: Cryptography: Author/Contact Info /msg mrbbking: Description: This is a complete and historically accurate implementation of the Vigenere cipher. The Atbash cipher uses a = −1. Our advanced Caesar Cipher Cipher; Description; Plaintext: Encrypted text: Key: Options; Alphabet; Blocks of five. How to Do a Modulo Calculation. The Affine cipher is a monoalphabetic substitution cipher, where each letter in the alphabet is mapped to another letter through a simple mathematical formula: (ax + b) mod 26. The number 26 represents the length of the alphabet and will be Vigenère can be described by 2 encryption methods (which arrive at the same result). In the next cell, I show how to do this with the use of a for loop. I have an encryption function $$E(p) = (ap + b) \\mod{26}$$ where the parameters are $a=7$, $b = 10$, and $p$ is the plaintext letter. Verify your answer below. Exercise 3: The so-called "Extended Euclidean Algorithm" is a mathematical procedure to find a-1 for any given key a. Find two plaintexts (input letters) that produce the same ciphertext (output letter). Caesar ciphers are encrypted by adding modulo 26 (C = p + key mod 26, where C is ciphertext and p is plaintext ) and are decrypted by adding the inverse of the key. Because of this, if you want to decipher the text without knowing the key, the mod 26, decode the result. Named after Julius Caesar, who used it for secret correspondence, the Caesar Cipher works by shifting each letter in the plaintext by a certain number of positions down the alphabet. 16 (Q) 13 (N) 21 (V) 25 (Z) (message + key) mod 26 E Q N V Z → ciphertext. Home which in this case is 21 (since 21 x 5 = 105 = 1 mod 26, as 26 x 4 = 104, and 105 - 104 = 1). CacheSleuth. Rot-13 (short for Rotation 13) is the name given to a mono-alphabetical substitution cipher which has the property of being reversible and very simple. Encrypt and decrypt any cipher created in a Vernam cipher. Affine cipher: Encode and decode . This analysis can cover all characters, but generally focuses on the letters of the alphabet (A-Z) and numbers (0 Example: D = 3, so $ 3 \times 17 \mod 26 \equiv 25 $ and the letter at rank 25 is Z. e a shifted twice So to wrap around modular arithmatic is needed. Method in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. 7 Linear Algebra for Cryptography 1 Codes can use ﬁnite ﬁelds as alphabets: letters in the message become numbers 0,1,,p−1. Supports. Recall that a=3 was a good key for the Multiplication Cipher MOD 26, so that we now encode the virus message using the good factor key a=3 and the final shift b=4. Crypto Corner. m = 26), there are a total of 286 non-trivial affine SPOILER ALERT: This is a writeup for the PicoCTF “Mod 26”, which will end up in showing the solution to the problem. Numbering the letters so A=1, B=2, etc is one of the simplest ways of converting them to numbers. It was used by Julius Caesar to encrypt messages with a shift of 3. sourav punoriyar We write mod 26 to mean we are doing arithmetic on a circle with 26 numbers, 0 through 25. 2. Affine cipher is one of the single transliteration ciphers that encrypts by replacing the characters in the text with other characters. Considering the specific case of encrypting messages in English (i. It has been described as the "Usenet equivalent printing an answer to a quiz upside down" as it provides virtually no cryptographic security. Using it, we arrive at 9(y +19) ≡ 9 · 3x ≡ x (mod 26). Each computed value The Affine cipher is a monoalphabetic substitution cipher, where each letter in the alphabet is mapped to another letter through a simple mathematical formula: (ax + b) mod 26. It's a type of substitution cipher in which each letter in the plaintext is shifted a certain number of places down or up the alphabet. Divide by p, keep the remainder. Calculate a mod b which, for positive numbers, is the remainder of a divided by b in a division problem. Example the letter M (12th letter) and key 16 The Affine cipher is a monoalphabetic substitution cipher, where each letter in the alphabet is mapped to another letter through a simple mathematical formula: (ax + b) mod 26. Contribute to isaaguilar/alphabet-encode-python development by creating an account on GitHub. The determinant of the Hill matrix must be prime with 26 to ensure that the matrix is invertible modulo 26 (the value 26 comes from the length of the Latin alphabet having 26 letters). 10. ) and all data download C = (a * P) mod 26. Decrypt the given The Affine cipher maps each letter in an alphabet to its numeric equivalent, encrypts it using a linear mathematical function, and converts it back to a letter. ) The replacement remains the same throughout the message, so the cipher is Cryptography Worksheet — The Aﬃne Cipher 1 The Aﬃne Cipher is a cipher that uses Maths to encode the message. Key Matrix: A = Encrypted Message: CIKKGEUWEROY The The Affine Cipher uses modulo arithmetic to perform a calculation on the numerical value of a letter to create the ciphertext. The biggest problem is that JavaScript doesn't contain a modulo operator. (usually 26 because that's the number of letters in the English language). The same algorithm as presented in Section 2. The value x is in the range 0 to 25, but if x + n or x − n are not in this range then 26 should be added or subtracted. This is equivalent to shift the alphabet (i. The result of a modulo 26 operation is always an integer between 0 and 25, encompassing 26 possible outcomes. . It assumes that you are using a ci = (pi + ki mod L) mod 26 After that, the ciphertext is expressed as letters instead of numbers. We have used the numbers 0 through 25 to represent 26 English letters, so we will use mod 26 in all of our cipher examples. If a number is larger than 26, then the remainder after subtraction of 26 is taken in modular arithmetic fashion. 3 A Hill Cipher multiplies blocks of the message by a secret matrix E (mod p). Text To Decode--a = b = a-1 = [ e(x)= (ax + b) mod 26 ] [ d(x)= a-1 (y - b) mod 26 ] Missing keys will be replaced by value of b=0 !! ENCODER/DECODER - AFFINE CYPHER: Text To Encode: Text To Decode--a = b = a-1 = [ e(x)= (ax + b) mod 26 ] [ d(x)= a-1 (y - b) mod 26 ] Missing keys will be replaced by value of b=0 !! Mod 26. Online affine cipher encoder and decoder, obtains the cipher text through a simple unary equation calculation on the encrypted letters, which is similar to the Caesar cipher principle, but has a Affine cipher is one of the single transliteration ciphers that encrypts by replacing the characters in the text with other characters. In affine cipher each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a For each letter of value x x of the plain text, is associated a value y y, result of the affine function y= A×x+B mod 26 y = A × x + B mod 26 (with 26 26 the alphabet size). for the famous RSA Cipher). The values of the alphabet characters start at 0 so A = 0, B = 1, etc. Calculators. m represents the type of character to convert. caesar cypher decryptor. , the row heading of the Vigenère table) to the right one position at a time. A shift of 0 or 26 would obviously result Tool to decode/encode messages created with the Option-key ⌥ available on Mac/Apple computers allowing to write special characters (symbols) as a cipher. This algorithm is used for various ciphers (i. For example, if the shift value is 3, the letter ‘A’ shifting the alphabet by n mod 26. According to The Code Book, by Simon Singh, (Doubleday, 1999, ISBN 0385495315) Blaise de Vigenere formalized this cipher system based on the earlier work of Battista Alberti, Johannes Trithemius and Giovanni Porta. I probably understand most of it but I don't get it why they use the mod 26 on line 8 alphabet=['a','b','c','d', A shift cipher, also known as a Caesar cipher, is a simple encryption technique that replaces each letter of a plaintext message with a letter a fixed number of positions down the alphabet. The determinant of the matrix we are inverting is ac - bd (mod 26) = 15*19 - 12*2 = 261 = 1 (mod 26). about the ROT13 cipher. We also need to find the inverse of the determinant (1), which luckily in this case is The Algebraic Nature of the Vigenère Cipher . Encrypt and decrypt text surrouned by minimal p a s t e l w a v e s. A Caesar cipher is when all the letters in a message are shifted the same number of spaces in 26 is the length of your dictionary, which happens to be the length of the English alphabet (A to Z). Decryption. The GROMARK Cipher is a Gronsfeld cipher using a mixed alphabet and a running key. This mapping is based on a mathematical function, called the Affine function, that The Caesar Cipher decoder is designed to decrypt messages created with one of the simplest and most widely known encryption techniques. 5*21 = 1 (mod 26). METHOD 1: Vigenere cipher by adding letters Vigenère cipher consists of adding the key to the plaintext. Hill Cipher explained and implemented in Python, C++, Java The Caesar Shift Cipher is a simple substitution cipher where the ciphertext alphabet is shifted a given number of spaces. The following letter addition calculations are actually number additions (the values of the letters are About Affine Cipher. Back to Tools. We discussed here that the alphabet is shifted to the left one position repeatedly to build the 26×26 Vigenère table. C=3" functions (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc. Decimal to text ; URL encode ; Enigma decoder ; Solution for Decode the following using the Vigenere Cipher (try the Mod 26 short out): Cipher: GBWYRGTCNIORXPNVKBTHQYOOZXBUKBXKXUZAODAPNVMBWXPDNLTXURCBF Key: Vigenère Cipher Decoder and Solver. actually you should use x + 26* k = x mod 26. A=1, B=2, Z=26, but any numeric conversion (like the Tool to decrypt/encrypt in Base 26. Here is a Python routine that encrypts a text: The Caesar Cipher is one of the earliest and simplest methods of encrypting text. 1. We must now perform the inverse calculations on the Explore the Caesar Cipher decoder, where each letter rotates a fixed number of positions. Digits. So on for each letter, the final (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc. [ E_n(x) = (x + n) \mod 26 \] where $x$ is the position of a letter in the alphabet (0-25), $n$ is the shift VIDEO ANSWER: We need to use the Caesar-Sieper function f of p which is equal to p plus 3 into mod 26 to solve this problem. Combining the French/Latin alphabet of 26 letters and an offset of 13, Rot-13 replaces a letter with another located thirteen places further down the alphabet. Character replacement is performed using the following formula. ) and all data download, script, or API access I'm trying to decrypt the ciphertext vczkh which I know was encoded using an affine cipher with the equation 7x + 8(mod 26). The modulo operation finds the remainder of a divided by b. if a*x = 1 (mod 26), then x is an inverse of a (and a is an It is a cipher key, and it is also called a substitution alphabet. Solution for Decode the message ACXUT CXRT, which was encrypted using the congruence c ≡ (3p + 5) mod 26 that corresponds to the previous table Use the RSA cipher with public key n = 713 = 23 · 31 and e = 43. The Hill cipher is an example of a block cipher. Relation to Modular Arithmetic. Linear Algebra for Cryptography 501 10. It is a basic cryptography method, often used for learning purposes. The challenge provides a ciphered message in red, which we’re supposed to decode. In the first solution, which d w g m e v x t is Common joke in cryptology community is ROT26 or double ROT 13 – notice, that shifting letter +26 mod 26 is actually turning around and no shifting! So ROT 13 is involution – that is its own inverse fucntion, both encrypting and decrypting! Those are very simple Additive/Substitution ciphers, but also must-know backgrounds 😊 Calculator Use. The following message was encoded using the key C = (3P + 4) mod 26. Using the modulo operator allows you to map every possible output of the matrix multiplication (encryption) to a letter in the alphabet (834 = 2 (mod 26) which is C), which lets you store the encrypted message in the form of a string of letters. 7. A block cipher is a cipher in which groups of letters are enciphered together in equal length blocks. this is just the definition of an inverse i. On Mac/Apple hardware, the keyboard has a special key called Option (⌥ symbol) which serves as a modifier to the or the "Option-Key Cipher" functions (calculate, convert, solve Find the value of the number mod 26. Thus our decoding function P = a-1*C MOD 26 tells us to simply multiply each cipher letter by the inverse of the encoding key a=5, namely by the decoding key a-1=21 MOD 26 and we can eventually decode: Cipher text PLAIN TEXT a 0 n For any integer 'a', the result of a modulo 26 operation is the remainder after dividing 'a' by 26. Suppose you intercept a (Here, "mod" refers to the modulo operation. 2 Linear Ciphers We can create somewhat more complex simple substitution ciphers by using linear functions along Alphabet base-26 cipher - encode and decode . Examples: 1 + 2 = 3 mod 26 13 x 2 = 0 mod 26, since 13*2 = 26 = 26(1) + 0 In order to decode this cipher the inverse of the key matrix A modulo 26 must be found. Caesar cipher program in c++. The number 26 represents the length of the alphabet and will be This tool is a versatile implementation of the Affine Cipher, a classical encryption algorithm that combines modular arithmetic and linear algebra. 4 To decode, multiply each block by the This is a complete guide to the Caesar cipher and the tools you need to decode it. Vigenere Tool (supporting English, French, German, Italian, Portugese, y= 5x+14 (mod 26) y+12 = 5x (mod 26) 21(y+12) = 21·5x (mod 26) 21y+18 = x (mod 26) Example. Di = (Ei - Ki + 26) mod 26. It enables users to encode and decode messages using a pair of keys, offering a 21, 15, 3. Shift (Caesar) Ciphers If you have a message you want to transmit securely, you can encrypt it (translate it into a secret code). The Hill cipher uses matrix multiplication, mod 26. In this case To recognize/guess the type of cipher/coding used to encrypt/encode a message, dCode uses several detection/cryptanalysis methods: — Frequency analysis: This involves observing which characters in the message appear most frequently and in what proportions. a shifted once (1+2) mod 26 = 3 (a becomes c) i. An Affine cipher is a type of monoalphabetic substitution cipher, in which each letter in the plaintext is mapped to a unique fixed letter in the ciphertext. Share. Modulo Cipher Encryption uses modular arithmetics and a sequence of numbers, characters must be converted into numbers, e. 考慮加密英文。（即： = ），不計26易凱薩密碼，總共有286非易仿射密碼。此數值是由於小於26之數中有12數與26互質。a Five Ways to Crack a Vigenère Cipher brought to you by The Mad Doctor ("madness") This is just a review of five nice ways to break a Vigenère cipher. (NOTE: it has been split into blocks of 5 le ©ers to make it easier to read) 因爲仿射密碼仍爲單字母表密碼，其依舊保留了該類別加密之弱處。當 = ，仿射加密為凱撒密碼，因該加密方程可簡化為線性移動。. ) and all data download, script Since the affine cipher is still a monoalphabetic substitution cipher, it inherits the weaknesses of that class of ciphers. Lower case. How this Algorithm works? Formula. The ROT cipher (or Rot-N), short for Rotation, is a type of shift/rotation substitution encryption which consists of replacing each letter of a message with another (always the same) located a little further (exactly N letters further) in the alphabet. Ei = (Pi + Ki) mod 26. The method is named after Julius Caesar, who used it in his private correspondence. Tap code ; I'm trying to decrypt the ciphertext vczkh which I know was encoded using an affine cipher with the equation 7x + 8(mod 26). The ﬁrst letter of the cipher alphabet (‘d’ in the original form) is the key of the cipher. Previous Obedient Cat Next Python Luckily for me I learned about ROT13 during my . For a simple substitution cipher, the set of all possible keys is the set of all possible permutations. ROT13 is one of the first Mentor: Good. We must now perform the inverse calculations on the integer values of the ciphertext. ROT13 (rotate by 13 places) replaces a letter with the letter 13 letters after it in the alphabet. Cipher; Description; Plaintext: Encrypted text: Key: Options; Alphabet; Blocks of five. To work with the affine cipher, and many other ciphers, we need to convert strings to lists of integers modulo $26$. Polybius Square a cipher where each alphanumeric (a-z, 0-9) character is represented by it’s coordinates in a grid. In order to create unique cipher characters, we must use a multiplier which is co-prime (the values do not share any factors when dividing - see Try GCD of 5) in relation to the size of the alphabet (26), so you should Cryptanalysis of the Hill Cipher. The modulo operation finds the remainder, so if you were dividing a by b and there was a remainder of n, you would say a mod b = n. It seems reasonable (at least to a mathematician like Sinkov) to consider what would happen if we encrypted by multiplying additive caesar shift code cipher solver Geocaching CacheSleuth. Key can be a ROT13 decoder: Decrypt and convert ROT13 to text . Ei: Encrypted text Pi: Plain Text values Ki: Plain Text values after adding key. However, there are more options such as ASCII codes, tap Tool to decrypt / encrypt using Base 37 (Alphanumeric + Separator) Cipher, an ideal base to encode alphanumeric strings with a number (and vice versa) with the mot common 37 characters (26 letters, 10 digits and 1 separator). Rot-13 coding is popular to hide content because it is easily reversible, Now to decode, the inverse of 5 modulo 26 is 21, i. Example We can encrypt Julius Caesar’s famous saying “Veni, Vidi, Vici” using a Caesar cipher with a key of ‘f’ as follows: Re-write the text to be enciphered to just use lower-case English characters. Here are some examples: What is 2 + 3 mod 5? 6. x is a letter replaced by a number from 0 to m - 1. The Affine cipher is a monoalphabetic substitution cipher, so all the methods that are used to cryptanalyse substitution ciphers The most common method of substitution replaces the 26 letters of the alphabet (one letter matches only one other). The One Time Pad is and by placing the symbol mod 26 after the calculation. – kelalaka. Trying to implement this algorithm in JavaScript without the use of a proper modulo operator will produce either incorrect results or a very cryptic and difficult to understand code. If we have a value x mod y, we divide x/y, and then the remainder of the problem is the mod. Named after Julius Caesar for secret communication. Most ciphers use modular arithmetic during some steps of the encryption and decryption process. You can see that C is the 3rd index, and P is in fact the 16th. For our purposes, think of modular arithmetic as division with remainders. An algorithmic way of expressing this cipher would be: [3] (plain_text_letter + key_digit) mod 26 = cipher_text_letter. Polybius Square About. 13's My Lucky Number. (We will discuss later how to test if a matrix has an inverse mod 26 or not. How does Affine cipher work? For this . Encrypt and decrypt any cipher created in a Affine cipher. Base 26 uses 26 symbols, by using the alphabet's letter, Base 26 cipher can encrypt words with numbers and conversely. Consider the following aﬃne cipher: y= 8x+7 (mod 26). One of the simplest ways to do this is with a shift cipher. This makes my decryption function p = (c – b) * a^-1 (mod 26) where b = 8, a = 7, c = number corresponding with cipher character starting from 0, and p is the same for plaintext. Cipher Letter A P I W X H R D D A Coded 1 15 8 22 23 7 17 3 3 00 Shifted 12 00 19 07 08 18 02 14 14 11 Letter M A T H I S C O O L 4. The for loop directs Sage to step through each character in the string and turn it $ E(i) = (i + n) \mod 26 $ where $ E(i) $ is the encrypted index of the letter, and $ \mod 26 $ denotes the remainder of division by 26, which corresponds to the number of letters in the English alphabet. Mathematical calculators. Perfect Decoding Uppercase letters (A-Z) Lowercase letters (a-z) Numbers (0-9) Symbols (!@#$ Justin works through the process of finding the decryption function of a given affine cipher. 2 of the text may be used: the matrix [ A | I ] is Vigenère cipher You are encouraged to solve this task according to the task description, using (keyFixed(keyI)-'A) IF tmp<0 THEN tmp==+26 FI out(0)==+1 out(out(0))='A+tmp MOD 26 keyI==+1 IF keyI>keyFixed(0) THEN keyI=1 FI OD RETURN PROC Encrypt(CHAR ARRAY in,key,out) Process(in,key,out,1) RETURN PROC Decrypt(CHAR I am trying to decipher a text from user without knowing the key in caesar cipher. Then multiply the inverse of the key by each pair of ciphertext letters (mod 26) to recover the original text. What is 22 + 7 mod 26? The Caesar Cipher and by placing the symbol mod 26 after the calculation. This multi decoder is designed to support a large number of codes and ciphers. This ensures that each modular multiplication operation remains one-to-one (each input vector/ngram corresponds to a single encrypted vector/ngram and vice versa). Aﬃne Ciphers An aﬃne cipher, (like a shift cipher), is an example of a substitution cipher: In encryption using a substitution 3 · 9 = 27 ≡ 1 (mod 26), so 9 is our desired multiplier. Famously, Julius Caesar used this N −→ 13 −→ 13+17 ≡ 4 (mod 26) −→ e Let’s think about security now. First of all, we need a key and a plaintext. The encryption key is a n x n matrix with an inverse mod 26, where n is the block size. The Caesar cipher is an Affine cipher with a = 1 since the encrypting function simply reduces to a linear shift. 0. The number 26 represents the length of the alphabet and will be The first step here is to find the inverse of a, which in this case is 21 (since 21 x 5 = 105 = 1 mod 26, as 26 x 4 = 104, and 105 - 104 = 1). Follow answered Jul 12, 2017 at 5:39. The fundamental principle of the Caesar Cipher is closely related to modular arithmetic. If this were not the case, Cryptography of Multiplicative Ciphers . This is mathematically denoted as 'a mod 26', read as " 'a' modulo 26". For instance, if you take the letter ‘A’ and count 13 letters after it, you end up on the letter ‘N’. Add a comment | Simple Affine Cipher Encrpytion Decryption. 2 The numbers are added and multiplied (mod p). I can produce two inputs that give the same output by ﬁnding two inputs that make “8x” equal to 0 mod 26. Hence the key is unique modulo 26, and En(x) = (x + n) mod 26. Dn(x) = (x – n) mod 26. The decoding function is The Affine cipher is a very insecure cipher, with the Caesar cipher possibly being the only easier cipher to crack. Additive Cipher Each character is added with this key number and the corresponding letter is substituted (mod 26). Addition in columns; Arithmetic sequence calculator; mod 26 O W K A C K M X G W N Caesar cipher: Encode and decode online . The Text after Encryption(Cipher text) is: XHRIP After Decryption the Text is: harry. Not all codes and ciphers have keywords, alphabets, numbers, letter translation, etc so if the code or cipher doesn't require it, those fields will be ignored. For example, the row of B is obtained by shifting the row of A to the left one position. Improve this answer. Here is an example of how to encode and decode one! Finding mod (modulo) 26 is simple, It is finding what the remainder would be when multiplied by the dividend (In most cases you can just minus them The final shift of 4 then produces the two cipher letters 4=e and the 17=r which makes the Cipher Code impossible to decode. But what if we want to encrypt the letter Y, at index 25?Well, what we do here is we loop back to the beginning; if we do this, the character 13 positions after it is in fact L!. Here's the quick version. Using a-1 = 17 in P=a-1 * C mod 26 yields eavesdropper. Encryption. This is a complete guide to the Vigenère cipher and the tools you need to decode it. [4] Adding Caesar cipher to it (1+Shift) mod 26 (1+1) mod 26 = 2 (a becomes b) i. Keep non-alphabet characters. g. c++ simple Caesar cipher algorithm. Mathematically, we can see that the index that would be position 26 is actually looping back to position 0, so we add on the 13 and take the remainder Convert numbers to letters in various formats. E(x) = (ax + b) mod m. 26 is already 0 in modulus 26. Description. I was asked to decrypt the Blaise de Vigenère created the Autokey Cipher in 1586! One cool feature of this cipher is that it makes use of the mod function in math. For a recap of how the Hill cipher works, see here. e. ) For our purposes, we will illustrate The crypted message is made of numbers between 1 and 26, sometimes the number 0 is used to code a space. Learn about its famous history and where it is still in use today, or use the Caesar Cipher tool to solve it automatically. Commented Oct 1, 2019 at 20:39. Upper case. This is called the A1Z26 cipher. So, applying ROT13 to ‘ABC’ would give you ‘NOP’. where d × d-1 = 1(mod 26), and adj(P) is the adjugate matrix of P. Related. In the context of the Hill Cipher, modulo 26 operations ensure Affine cipher online encoder and decoder. — Map, for each letter, the value of its rank in the alphabet, starting from 0: A=0,B=1,,Z=25. The Affine cipher is a type of monoalphabetic substitution cipher, wherein each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter. Below is the table for alphabets. You can also choose a different starting point to cipher the message. This is the basis of the famous Caesar cipher and its many Hill Cipher. Decode it. 2 of the text may be used: the matrix [ A | I ] is Vernam cipher online encoder and decoder. we apply the mod = a x + b mod m. Exercise 2: Now decode "oapoyrbkhhob" by hand knowing that it was encrypted using a=23. Thus, for the English alphabet, the number of keys is 26! (factorial of 26), which is about . $$ d(y)=a^{-1}*(y-b)\mod m$$ where $$ a^{-1}$$ It was more popular than the Vigenère cipher, despite its limitations. ghgcoapez cuzw jrnpvy qvvbg wjo acwf gngsvu kfjcco mit naip nxavvt gzusw gfqflrb xbyzt rbt