A Hybrid-Encryption Algorithm Based On DES And RSA Algorithm

Cryptography is the key to ensure the confidentiality of the information and core. The research about information encryption algorithm is one of the very important and effective measures to protect the security and integrity of information. In this paper, we deeply analyze the DES and RSA algorithm which is representation of the symmetric cryptosystem and the asymmetric cryptosystem. We gain the advantages and disadvantages of each algorithm and give some appropriate improvements by making use of prefix codes and methods in combinatorial mathematics. Based on making use of encrypting the cipher code of DES by RSA, we combine the virtues of the two algorithms and propose a kind of hybrid-encryption algorithm which according to them.At the first, DES is the most typical Symmetric encryption algorithm so far. It can be used in many aspects and it is a representation of the block cipher. It contains a64bit plaintext and a64bit key. Actually, there are only56bits data in the calculation and8bit data of them is used in the even-odd check. After a series of replacement calculation, the plaintext is encrypted. DES has great encryption efficiency. So, numerous data can be encrypted by this algorithm. In addition, people are of the opinion that it is the most difficult thing to break the RSA so far. It can not only be used to encrypt the data, but also digital signature. The key length of RSA is usually1024bits, but the length maybe2048bits in some system which has a high security requirement. If the prime number is big enough, it is impossible to break RSA. However the encryption efficiency of RSA is slow, especially when encrypting lots of data.Next, we purpose two improvements for DES algorithm which are3-DES and the recombination of S-box.3-DES adds one or two keys to the algorithm and then the key length can run up to112bits. The complexity of attacking also increases and the3-DES algorithm can’t be break. The S-box which is the core for DES algorithm is only nonlinear part of the DES algorithm. According to the idea of the whole arrangement in combinatorial mathematics and the characteristic that prefix codes can decode the code, we put forward a new way to recombinant the S-box. Let the sub key which produced in the progress of the block encryption algorithm each round control the order of the S-box. So that, the using order of S-box in the progress of encrypting plaintext is different for each round of iteration and achieve the effect which called one time one key. The new method can improve the security effectively and the ability to struggle the attack. At the same time, because of the short length of the key of DES and the high security performance of RSA, we encrypt the key of DES by RSA algorithm and encrypt the plaintext by DES algorithm. The new hybrid-encryption algorithm uses RSA to ensure the security and use DES to ensure the efficiency. This is a kind of great algorithm. The new algorithm can not only ensure the efficiency, but also can improve the security. In this paper, we achieve the hybrid-encryption algorithm on VC++and find that it has a quick encrypting speed and high quality of security. It can be used to encrypt a lot of data and digital signature. It will have a widespread application prospect.