Abstract—The Vigenère encryption is a method that enciphers original text by adding a continuously changing correspondence of keys into plain text by means of one to one correspondence. A simple example would be to match A with 0, B with 1, and so on until Z is matched with 25. The weakness of the Vigenère encryption is that the code can be broken without the key by guessing its length. We attempted to strengthen the Vigenère encryption by multiplying the length of "key groups" so that the length of the final key would be amplified. This study reveals that the security of the Vigenère cipher, once thought to be low, can be supplemented through the use of an effective key.

Index Terms—vigenère cipher, divided keys, ASCII, key length, least common multiple, kasiski, friedman, key-amplified

Cite: Ahhyun Ahn, Dooyoung Kim, and Taeseon Yoon, "Key-Amplified Cipher," Lecture Notes on Information Theory, Vol. 2, No. 1, pp. 54-60, March 2014. doi: 10.12720/lnit.2.1.54-60