# Polyalphabetic cipher encryption and decryption program in c. VigenĂ¨re Cipher Algorithm Program in C/C++ 2022-10-04

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A polyalphabetic cipher is a type of encryption algorithm that uses multiple substitution alphabets to obscure the meaning of a message. The basic idea behind a polyalphabetic cipher is to use multiple substitution alphabets, rather than just one, to obscure the message. This makes it more difficult for attackers to break the cipher, as they must determine which alphabet was used for each letter of the message.

One popular example of a polyalphabetic cipher is the VigenĂ¨re cipher, which was invented in the 16th century and is still in use today. The VigenĂ¨re cipher uses a series of interwoven Caesar ciphers, each with a different shift value, to encrypt the message. The shift value for each Caesar cipher is determined by a key word, which is used to generate a repeating sequence of shift values.

To implement a polyalphabetic cipher in C, we will first need to define a function for encrypting a message using a given key. This function will take two arguments: the message to be encrypted, and the key. It will return the encrypted message.

The first step in the encryption process is to convert the message and the key into arrays of integers, with each integer representing the position of a letter in the alphabet. For example, the letter 'A' would be represented as 0, 'B' as 1, and so on.

Next, we will iterate through the message array and use the corresponding value in the key array to determine the shift value for the current letter. We will then apply the Caesar cipher to encrypt the current letter using this shift value.

Finally, we will return the encrypted message as a string.

To decrypt a message encrypted with this cipher, we will simply need to define a function that performs the inverse operation. This function will take the same arguments as the encryption function, but will return the decrypted message rather than the encrypted message.

To decrypt the message, we will again convert the message and the key into arrays of integers, and then iterate through the message array. For each letter in the message, we will use the corresponding value in the key array to determine the shift value, and then apply the inverse of the Caesar cipher to decrypt the letter.

By following these steps, we can create a simple polyalphabetic cipher program in C that can encrypt and decrypt messages using a variety of substitution alphabets. While this type of cipher can be effective at obscuring the meaning of a message, it is still vulnerable to certain types of attacks, such as frequency analysis, and should be used in conjunction with other security measures to provide robust protection for sensitive information.

## Vigenere Cipher in C and C++

So my is encoded as CM. Also Read: Also Read: Vigenere Cipher Encryption Message Text: THECRAZYPROGRAMMER Key: HELLO Here we have to obtain a new key by repeating the given key till its length become equal to original message length. On the other hand, Private key is only used to decrypt the encrypted message. This program performs encryption and decryption using a monoalphabetic cipher. The next letter of the key is chosen, and that row is gone along to find the column heading that matches the message character. It employs a form of Algorithm It is similar to Awould become D, Bwould become E, Ywould become Band so on.

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## C Program To Encrypt And Decrypt The String (Source Code)

It involves the use of public and private key, where the public key is known to all and used for encryption. After filling it, we traverse the matrix in zig-zag manner to obtain the original text. Vigenere Cipher is kind of polyalphabetic substitution method. Repeat the same process for all remaining alphabets in message text. The best-known multiple-letter encryption which treats diagrams from the plaintext as solitary units and contrasts these components to ciphertext diagrams.

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## Rail Fence Cipher

Thus the alphabets of the message are written in a zig-zag manner. For example x, so balloon could be enciphered as ba lx lo on. Encryption Key: WELCOME Message: Thisistutorialspoint Here we have to obtain a key by repeating the given key till its length becomes equal to original message length. If the user enters other value than 1 or 2 it will show Invalid Input. Here is source code of the C Program to Implement the Monoalphabetic Cypher. Break down Vigenere Cipher Table, search for letters in order An in segment H, the comparing line will be the primary letters in order of unique message for example T. Therefore, hs become BP and ea becomes more IM or even JM, since the encipherer wants.

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## Caesar Cipher in C and C++ [Encryption & Decryption]

Here you get encryption and decryption program for hill cipher in C and C++. To encrypt, a table of alphabets can be used, termed VigenĂ¨re squareor VigenĂ¨re table. Your code does not work proper way. Playfair Cipher Program in C In this program, we have entered the MONARCHY and the message as LEARNPROGRAMO and the final message is printed on the screen. For decryption just follow the reverse of encryption process. For encryption and decryption, Vigenere Cipher Table is utilized in which letters in order from start to finish are written in 26 lines.

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## VigenĂ¨re Cipher Algorithm Program in C/C++

Its encryption will be done row wise i. The VigenĂ¨re cipher has several Caesar ciphers in sequence with different shift values. Therefore, row Land column Aof the VigenĂ¨re square are used, namely L. Take the alphabet in Vigenere Cipher Table where T row and W column coincides i. Repeat this process for all the alphabets in encrypted message.

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## C code to Encrypt & Decrypt Message using Vernam Cipher

A couple of hundred letters of ciphertext are usually adequate. Get program for caesar cipher in C and C++ for encryption and decryption. Also Read: Encryption: The given message string and key string is represented in the form of matrix. It is used for encryption of alphabetic text. This is a C Program to implement Monoalphabetic Cipher.

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## Hill Cipher in C and C++ (Encryption and Decryption)

The rail fence cipher also called a zigzag cipher is a form of transposition cipher. To learn more about hill cipher you can visit following link. Take the alphabet in Vigenere Cipher Table where T row and H column coincides i. The relative frequencies of individual letters show a much larger variety than that of diagrams. The cipher text can be generated by below equation. Next, in row E from L EMON , the ciphertext Xis located in column T.

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## Hill Cipher in C and C++ (Encryption and Decryption)

Here you get encryption and decryption program for hill cipher in C and C++. Vigenere Cipher Encryption Message Text: JUSTTECHREVIEW Key: HELLO Here we need to acquire another key by rehashing the given key till its length become equivalent to unique message length. At long last modulo 26 is taken for every component of the network got by the increase. For While encrypting the given string, 3 is added to the ASCII value of the characters. For encryption and decryption Vigenere Cipher Table is used in which alphabets from A to Z are written in 26 rows. Unique Message: JUSTTECHREVIEW The above procedure can be spoken to in arithmetical structure by the following condition. The Playfair cipher is a Fantastic improvement over easy monoalphabetic ciphers.

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