__link__: Vigenere Algorithm

While the Vigenère algorithm is no longer secure enough for modern data (it can be cracked in seconds by a basic script), it remains a fundamental concept in computer science and cryptography education. It served as the bridge between ancient manual encryption and the complex polyalphabetic machines of WWII, like the German Enigma.

In 1863, Kasiski published a formal method for breaking it. His strategy, the Kasiski Examination , involved looking for repeated fragments in the ciphertext. By measuring the distance between these repetitions, an analyst could deduce the length of the keyword. Once the key length was known, the ciphertext could be treated as several intertwined Caesar ciphers, which are easy to solve. Modern Legacy vigenere algorithm

The "indecipherable" label was finally stripped away in the mid-19th century. While the Vigenère algorithm is no longer secure

For centuries, the Vigenère algorithm stood as the "le chiffre indéchiffrable" (the indecipherable cipher). While simple substitution ciphers like the Caesar cipher were easily broken by frequency analysis, the Vigenère offered a level of complexity that baffled the world’s greatest cryptanalysts for nearly 300 years. His strategy, the Kasiski Examination , involved looking

If you prefer math over charts, the algorithm can be expressed using modular arithmetic. Let Decryption: (Where is the plaintext, is the key, and is the ciphertext.) Why It Was So Strong

The Vigenère Cipher: Unlocking the "Indecipherable" Algorithm