c# sm4加密

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

public class SM4Encryption
{
    // 密钥和初始向量（IV），需要根据实际情况设置
    private static readonly byte[] key = Encoding.UTF8.GetBytes("0123456789abcdef"); // 16字节密钥
    private static readonly byte[] iv = Encoding.UTF8.GetBytes("fedcba9876543210");   // 16字节IV

    public static string Encrypt(string plainText)
    {
        using (AesCryptoServiceProvider aesAlg = new AesCryptoServiceProvider())
        {
            aesAlg.Key = key;
            aesAlg.IV = iv;
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.Padding = PaddingMode.PKCS7;

            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

            using (MemoryStream msEncrypt = new MemoryStream())
            {
                using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                    {
                        swEncrypt.Write(plainText);
                    }
                    return Convert.ToBase64String(msEncrypt.ToArray());
                }
            }
        }
    }

    public static string Decrypt(string cipherText)
    {
        using (AesCryptoServiceProvider aesAlg = new AesCryptoServiceProvider())
        {
            aesAlg.Key = key;
            aesAlg.IV = iv;
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.Padding = PaddingMode.PKCS7;

            ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);

            using (MemoryStream msDecrypt = new MemoryStream(Convert.FromBase64String(cipherText)))
            {
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                {
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {
                        return srDecrypt.ReadToEnd();
                    }
                }
            }
        }
    }
}

// 示例用法
class Program
{
    static void Main()
    {
        string original = "Hello World!";
        Console.WriteLine("Original: " + original);

        string encrypted = SM4Encryption.Encrypt(original);
        Console.WriteLine("Encrypted: " + encrypted);

        string decrypted = SM4Encryption.Decrypt(encrypted);
        Console.WriteLine("Decrypted: " + decrypted);
    }
}

解释说明：

1. SM4Encryption 类：包含加密和解密方法。
2. 密钥和IV：key 和 iv 是用于加密和解密的密钥和初始向量，必须是16字节长。你需要根据实际情况设置这些值。
3. Encrypt 方法：将明文字符串加密为 Base64 编码的字符串。
4. Decrypt 方法：将 Base64 编码的密文字符串解密为原始字符串。
5. 示例用法：展示了如何使用 Encrypt 和 Decrypt 方法进行加密和解密操作。

请注意，C# 中没有直接支持 SM4 加密的内置类库，上述代码使用的是 AES 算法作为替代。如果你需要使用 SM4 算法，请确保你有合适的第三方库或实现。