基于Rijndael算法的动态密钥和算法实现

The Dynamic Key and Algorithm Implementation Based on Rijndael

通过对Rijndael算法研究，结合C语言中所带的函数rand（）及计算机系统的时问作为该函数的种子产生的伪随机数，构造动态密钥以及动态加密算法和计算机程序实现。运用这个算法使得用同一个密钥只要时间不同，不管相同的明文被加密多少次，其密文一般都是不同的。动态加密算法解决了用户总是频繁更换手中的密钥这个令人烦恼的问题，使加密明文变得更容易、更方便和更安全。从动态加密算法中我们看到，动态加密对密码攻击者而言，无论是选择明文、已知明文、选择密文攻击均是极其困难的。对加密用户来说，只要密钥保护得当，可以长时间不必更换密钥，所以使加密的信息变得更加安全了。

Through studying on the Rijndael encryption algorithm, combining the algorithm with the function RAND （） of C language and taking computer system time as a seed to generate the pseudorandom number from the function, we construct dynamic keys and a dynamic encryption algorithm, and implement of computer programs. The algorithm allows a key to encrypt the same plaintext many times and the corresponding ciphertexts are different if encryption time does alter. The dynamic encryption algorithm doesn＇t only solve the problem of vexing users to modify keys frequently but also enables to encrypt a plaintext more easily, more conveniently and more securely. From the dynamic encryption algorithm we find that it is extremely difficult for an attacker to break a ciphertext using chosen plaintext, known plaintext, or chosen-ciphertext. For encryption users, as long as the key is protected well, he doesn＇t need to modify the key for a long time. Therefore, encrypted information becomes more secure