对称算法又称为传统密码算法。对称算法的对称性体现在加密密钥能够从解密密钥推算出来, 反之亦然。在大多数对称算法中, 加解密的密钥是相同的。可见, 对称密钥算法的加解密密钥都是保密的。对称密钥算法又分为两种分组密码和流密码。分组密码将明文分割为若干个定长的数据块称为一个分组, 每次对一个分组进行处理流密码又称序列密码, 依次对输人每个元素进行处理。DES算法是一种最通用的对称密钥算法, 属于分组密码算法。-Symmetric algorithm, also known as the traditional cryptographic algorithms. Reflected in the symmetry of symmetric algorithm encryption key can decrypt the keys derived from, and vice versa. In most symmetric algorithms, encryption and decryption key are the same. Visible, symmetric key encryption algorithm key are confidential. Symmetric key algorithm is divided into two block ciphers and stream ciphers. Cipher the plaintext is divided into a number of fixed-length blocks of data called a packet, each packet processing on a stream cipher, also known as cipher, each element in turn for processing the input. DES algorithm is a symmetric key algorithm is the most common, is block cipher.