GCMEncrypt 可鉴别加密函数 (GCM-AE(k)) K: 对称密钥 IV: IV向量 P: 明文 A: 附加的鉴别数据 return: 密文, 鉴别标签.

GetH 对“0”分组的加密得到 GHASH泛杂凑函数的子密钥 key: 对称密钥 return: GHASH泛杂凑函数的子密钥.

GetY0 生成初始的计数器时钟J0 H: GHASH自密钥 IV: IV向量 return: 初始的计数器时钟(J0).

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.

Sm4GCM SM4 GCM 加解密模式 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.

Cipher is an instance of SM4 encryption.