Vigenere cipher

The Vigenere cipher is a sequence of Caesar ciphers with changing shift coefficients depending on the key. The service allows encrypting and decrypting texts in Cyrillic and Latin scripts, considering the case of letters and additional non-alphabetic characters. The key must contain fewer characters than the encoded message.

The Vigenere cipher is a classic encryption method developed in the 16th century by the French diplomat and cryptographer Blaise de Vigenere. This encryption method is an example of polyalphabetic substitution, where each letter in the plaintext is replaced by the corresponding letter in the ciphertext using a keyword or phrase.

The encryption process using the Vigenere cipher is based on a table known as the Vigenere table or square. This table is a matrix where the letters of the alphabet are repeated in rows and columns. The keyword or phrase is used to determine the row shifts in the table, which defines the substitution of each letter in the plaintext with the corresponding letter in the ciphertext.

The encryption process using the Vigenere cipher involves the following steps:

1. Prepare the keyword: Choose a keyword or phrase that you will use for encrypting and decrypting the message. The keyword should be the same length or longer than the plaintext.

2. Create the Vigenere table: Based on the keyword, create the Vigenere table. Place the keyword in the first row of the table and then repeat it until the end of the table. Fill the remaining part of the table with the other letters of the alphabet.

Vigenere Table. Keyword: KEY
	K	E	Y
K	E	Y	K
E	Y	K	E
Y	K	E	Y
K	E	Y	K

3. Transform the plaintext: Replace each letter in the plaintext with the corresponding letter in the Vigenere table. Move along the rows and columns of the table, using the letters of the keyword as pointers for substitution.

4. Obtain the ciphertext: Record each substituted letter, and this will be your ciphertext.

The decryption process using the Vigenere cipher is performed in reverse order. Using the same Vigenere table and keyword, you can replace each letter in the ciphertext with the corresponding letter in the plaintext.

The Vigenere cipher is a polyalphabetic cipher, making it more complex to break. Unlike simple substitution ciphers, the Vigenere cipher takes into account the frequency of letters in the language and complicates the task for cryptanalysts.

However, it is important to note that the Vigenere cipher is not absolutely impenetrable and can be cracked by key guessing or using other cryptanalytic methods.

In conclusion, the Vigenere cipher remains an interesting and historically significant encryption method that provides a degree of confidentiality and data protection during information transmission.

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