对称/分组密码一般分为流加密(如OFB、CFB等)和块加密(如ECB、CBC等)。对于流加密，需要将分组密码转化为流模式工作。对于块加密(或称分组加密)，如果要加密超过块大小的数据，就需要涉及填充和链加密模式，文中提到的ECB和CBC等就是指链加密模式。 本文将要介绍了AES对称加密/分组加密/流密码及其ECB、CBC、CFB、OFB和CTR五种对称加密模式。-Symmetric/block ciphers are generally divided into stream encryption (eg, OFB, CFB, etc.) and block encryption (such as ECB, CBC, etc.). For streaming encryption, block cipher needs to be translated into the work flow model. The encryption block (or block cipher), If you want to encrypt the data block size more than on the need to involve filling and chain encryption mode, the text referred to, such as ECB and CBC encryption mode refers chain. This paper will be introduced the AES symmetric encryption/packet encryption/stream cipher and the ECB, CBC, CFB, OFB and CTR mode in five symmetric encryption.