# Vigenere cipher program in c. Vigenere Cipher using C++ 2022-10-10

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The VigenĂ¨re cipher is a method of encrypting alphabetic text. 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 VigenĂ¨re square or VigenĂ¨re table.

The table consists of the alphabets written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet. At different points in the encryption process, the cipher uses a different alphabet from one of the rows. The alphabet used at each point depends on a repeating keyword.

To generate the key, we first create a matrix of alphabets A-Z. The key is then written horizontally at the top of the matrix. The length of the key must be less than or equal to the length of the message.

For example, if our message is "HELLO" and our key is "ABC", the first letter of the message will be encrypted using the first letter of the key, the second letter using the second letter, and so on. When we reach the end of the key, we start again from the beginning.

To encrypt the message, we match the row with the key letter and the column with the message letter. The letter in the intersecting cell is the encrypted letter.

To decrypt the message, we use the same process but this time we match the row with the key letter and the column with the encrypted letter. The letter in the intersecting cell is the original message letter.

Now that we have a basic understanding of the VigenĂ¨re cipher, let's implement it in C.

First, we need to include the necessary libraries and define the key and message as strings:

#include <stdio.h> #include <string.h>

char key[] = "ABC"; char message[] = "HELLO";

Next, we define the functions for encrypting and decrypting the message:

void encrypt() { int i, j; char encrypted[strlen(message)];

``````for(i = 0, j = 0; i < strlen(message); i++, j++)
{
if(j == strlen(key))
{
j = 0;
}

encrypted[i] = (message[i] + key[j]) % 26;
}

printf("Encrypted message: %s\n", encrypted);
``````

}

void decrypt() { int i, j; char decrypted[strlen(message)];

``````for(i = 0, j = 0; i < strlen(message); i++, j++)
{
if(j == strlen(key))
{
j = 0;
}

decrypted[i] = (message[i] - key[j] + 26) % 26;
}

printf("Decrypted message: %s\n", decrypted);
``````

}

Finally, we can call these functions in the main function:

int main() { printf("Original message: %s\n", message);

``````encrypt();
decrypt();

return 0;
``````

}

And that's it! We now have a working VigenĂ¨re cipher program in C. This program can be used to encrypt and decrypt messages using the VigenĂ¨re cipher. Of course, this is just a basic implementation and there are many ways to improve upon it

## Vigenere cipher C program

Consider using pointers instead of indexing Using pointers effectively is an essential skill for every C programmer. It is utilized for encryption of alphabetic content. But another reason to define constants is that they act as comments. There's no functional reason for this. I have had some previous classroom experience with C before CS50, but still consider myself a beginner. The jaws that bite, the claws that catch! The program output is also shown below.

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## Vigenere Cipher in C

This means that two different chiper methods will work in the same place with a menu. The formula reads more naturally with the constant. Analyze Vigenere Cipher Table, look for alphabet P in column W, the corresponding row will be the first alphabet of original message i. Also, for clarity's sake you should try to be consistent. If any character in plaintext is non-alphabetical, it just prints it out in its original form.

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## C programming

. At different points in the encryption process, the cipher uses a different alphabet from one of the rows. Assumptions We assume that for both C++ classes VigenereEncrypt and VigenereDecrypt, code word consists entirely of letters, but the text might contain non-letter characters. Here is source code of the C Program to Implement the Vigenere Cypher. If you could critique my code that would be great. There is a class and some pointers, but they do not work in the switch- case statement, so I need help.

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## Vigenere Cypher Program in C

I received full credit for my answer, but I still want to clean up the code if possible. Take the letters in order in Vigenere Cipher Table where T line and H section harmonizes for example A. Polyalphabetic Cipher is also based on substitution techniques, but here we are using multiple substitution alphabets, so as to increase the security context of an algorithm. Repeat this process for all the alphabets in encrypted message. The only thing that I'd say is that I like having the declaration and the initialization on the same line.

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## performance

New Generated Key: HELLOHELLOHELLOHEL For encryption take first letter of message and new key i. } This can be one level of conditionals: if isupper. I do not see how string is adding any clarity here, particularly when defined hidden in an external include. Thus Tis the second plaintext letter. It is a simple form of polyalphabetic substitution. The VigenĂ¨re cipher has several Caesar ciphers in sequence with different shift values.

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## C++ Vigenere and Caesar cipher in the same programming with switch case

Now you have to look up in the table â€” labelled as Plaintext letters in the left and top letters are the key. Original Message: THECRAZYPROGRAMMER Above process can be represented in algebraic form by following equation. . Those rotor machines are also based on Polyalphabetic substitution cipher. This is going to make the islower and isupper checks fail every subsequent iteration. For example, in row A from AYUSH , the ciphertext G appears in column G, which is the first plaintext letter.

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

However, i cannot added Vigenere. To learn more, see our. A real VignĂ¨re cipher, in contrast, can encode arbitrarily large messages, by re-using the key every strlen key input characters. . The encrypt function returns the encrypted string, in all caps. Repeat the same process for all remaining alphabets in message text.

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## Vigenere Cipher in C and C++

So then the reader of the code has to try to figure out if it's an indentation error or a missing braces error. . It is used for encryption of alphabetic text. For example you have you have to methods to encrypt and decrypt. Rather than two levels of conditionals: if isalpha. See below table As you can see the key is repeated, it will be similar in size to that of plaintext like above.

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## beginner

This explains how a VignĂ¨re cipher is less secure than OTP, particularly for short keys - but it's much more usable. In cryptography, Caesar shift is one of the simplest known encryption techniques. This also takes into account wrapping of the key array if the key array is smaller than plaintext, then once the last character in key is used to encrypt a character in plaintext, the next character should start over from the beginning of key and also takes into account maintaining the case of the character of plaintext if plaintext! Repeat the same process for all remaining alphabets in message text. . The cipher text can be generated by below equation.

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