![]() ![]() ![]() If a cryptanalyst correctly guesses the key's length, then the ciphertext can be treated as interwoven Caesar ciphers, which individually are easily broken. The primary weakness of the Vigenère cipher is the repeating nature of its key. However, using the Vigenère cipher, E can be enciphered as different ciphertext letters at different points in the message, thus defeating simple frequency analysis. ![]() For instance, if P is the most frequent letter in a ciphertext whose plaintext is in English, one might suspect that P corresponds to E because E is the most frequently used letter in English. The idea behind the Vigenère cipher, like all polyalphabetic ciphers, is to disguise plaintext letter frequencies, which interferes with a straightforward application of frequency analysis. Phrase LEMON, for example, defines the sequence of ROT11-ROT4-ROT12-ROT14-ROT13, which is repeated until all block of text is encrypted.Īs wikipedia tells us, it is a simple form of polyalphabetic substitution. The sequence is defined by keyword, where each letter defines the needed shift. For example, the first letter of text is transformed using ROT5, second - using ROT17, et cetera. Vigenère cipher is the sequence of Caesar ciphers with different transformations (ROTX, see Caesar cipher). Here is the calculator, which transforms entered text (encrypt or decrypt) using Vigenere cipher. Since we already have Caesar cipher, it seems logical to add the Vigenère cipher as well.
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