Three-Pass Protocol Implementation in Vigenere Cipher Classic Cryptography Algorithm with Keystream Generator Modification

摘要

Vigenere Cipher is one of the classic cryptographic algorithms and includedinto symmetric key cryptography algorithm, where to encryption and decryptionprocess use the same key. Vigenere Cipher has the disadvantage that if keylength is not equal to the length of the plaintext, then the key will berepeated until equal to the plaintext length, it course allows cryptanalysts tomake the process of cryptanalysis. And weaknesses of the symmetric keycryptographic algorithm is the safety of key distribution factor, if the key isknown by others, then the function of cryptography itself become useless. Basedon two such weaknesses, in this study, we modify the key on Vigenere Cipher, sowhen the key length smaller than the length of plaintext entered, the key willbe generated by a process, so the next key character will be different from theprevious key character. In This study also applied the technique of Three-passprotocol, a technique which message sender does not need to send the key,because each using its own key for the message encryption and decryptionprocess, so the security of a message would be more difficult to solved.