1.SymmetricAlgorithm.Key Property
获取或设置对称算法的密钥
类型：byte[ ]
The secret key is used both for encryption and for decryption. For a symmetric algorithm to be successful, the secret key must be known only to the sender and the receiver. The valid key sizes are specified by the particular symmetric algorithm implementation and are listed in the LegalKeySizes property.
If this property is null when it is used, the GenerateKey method is called to create a new random value.
2.SymmetricAlgorithm.LegalKeySizes Property
Gets the key sizes, in bits, that are supported by the symmetric algorithm.
类型：KeySizes[]
3.CryptoStream.FlushFinalBlock Method
//用缓冲区的当前状态更新基础数据源或存储，然后清空缓存。
Updates the underlying data source or repository with the current state of the buffer, then clears the buffer.