Enhanced hybrid encryption method using the Half-Key exchange and the dynamic S-Box and Shift-Row in AES

Abstract

Hybrid encryption algorithm has the advantages of both symmetric encryption algorithm and asymmetric encryption algorithm. When one sends a symmetric key to the other, it encrypts the symmetric key with asymmetric encryption algorithm. Therefore, the hybrid encryption algorithm made up for the weak point of key stealing. Nevertheless, since the hybrid encryption algorithm applies symmetric encryption algorithm to data encryption, it is possible to decrypt data through symmetric key brute force attack. To overcome the disadvantage, this study first divided a symmetric key in half and let a sender and a receiver have each Half-Key, and then used asymmetric encryption algorithm to encrypt and exchange Half-Key and decrypt and complete one symmetric key. In addition, the Half- Key of a sender and of a receiver was used to modify S-Box of conventional AES, and Key-Schedule Shift direction was changed in the Key-Schedule process. As a result, in spite of key stealing, it was impossible to decrypt data with conventional AES. In the case of conventional AES, when brute force attack is carried out on a symmetric key, it is possible to find the key after number of up to 2128 cases is calculated. However, in the proposed method, when brute force attack is made on a symmetric key and S-Box, it is required to calculate number of up to 22048 cases to find the key. Therefore, it was found that the proposed method improved security more than existing hybrid encryption & decryption scheme. © 2016 International Information Institute.