# Functions
NewCipher creates and returns a new cipher.Block.
ReadKeyFromPem will return SM4Key from PEM format data.
ReadKeyFromPemFile will return SM4Key from filename that saved PEM format data.
密码反馈模式（Cipher FeedBack (CFB)）https://blog.csdn.net/zy_strive_2012/article/details/102520356https://blog.csdn.net/sinat_23338865/article/details/72869841.
Paper: The Galois/Counter Mode of Operation (GCM) David A.
输出反馈模式（Output feedback, OFB）https://blog.csdn.net/chengqiuming/article/details/82390910https://blog.csdn.net/sinat_23338865/article/details/72869841.
WriteKeyToPem will convert SM4Key to PEM format data and return it.
WriteKeyToPemFile will convert SM4Key to PEM format data, then write it into the input filename.