C# 使用国密SM4加密解密

首先需第三方Nuget包：Portable.BouncyCastle （源码来自http://www.bouncycastle.org/csharp/），支持.NET 4,.NET Standard 2.0

使用BouncyCastle指定填充方案

零填充（Zero Padding）

PKCS7填充（PKCS7 Padding）

示例（SM4 CBC 模式加密（使用 Zero Padding））

代码解析

使用BouncyCastle指定填充方案

在BouncyCastle中，可以通过选择不同的PaddedBufferedBlockCipher实现来指定填充方案。这里我们将展示如何使用零填充（Zero Padding）和PKCS7填充（PKCS7 Padding）。

零填充（Zero Padding）

对于零填充，您需要自定义填充处理，因为BouncyCastle不直接提供零填充实现。

PKCS7填充（PKCS7 Padding）

如果你想使用PKCS7填充，可以使用BouncyCastle中的PaddedBufferedBlockCipher类直接指定Pkcs7Padding。

示例（SM4 CBC 模式加密（使用 Zero Padding））

采用国密SM4 CBC 模式加密（使用 Zero Padding）

SM4HttpUtilsV2.cs

using System;
using System.Collections.Generic;
using System.Security;
using System.Security.Cryptography;
using System.Text;
using Newtonsoft.Json;
using System.Net.Http;
using System.Threading.Tasks;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Crypto.Paddings;public class SM4HttpUtilsV2
{public static Dictionary<string, string> CreateCommonParam(string appKey, string appSecret, string codeData, string iv){// 时间戳long timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();// 签名 appKey + apiAppInfo.getAppSecret() + encryptString + timestampConsole.WriteLine($"签名: {appKey}{appSecret}{codeData}{timestamp}{iv}");Console.WriteLine($"appKey={appKey}");Console.WriteLine($"appSecret={appSecret}");Console.WriteLine($"encryptStr={codeData}");Console.WriteLine($"timestamp={timestamp}");Console.WriteLine($"iv={iv}");// 使用 MD5 生成签名string sig = CalculateMD5Hash(appKey + appSecret + codeData + timestamp + iv);Console.WriteLine($"签名值: {sig}");var requestParam = new Dictionary<string, string>{{ "timestamp", timestamp.ToString() },{ "sign", sig },{ "iv", iv }};return requestParam;}private static string CalculateMD5Hash(string input){using (var md5 = MD5.Create()){byte[] inputBytes = Encoding.UTF8.GetBytes(input);byte[] hashBytes = md5.ComputeHash(inputBytes);StringBuilder sb = new StringBuilder();for (int i = 0; i < hashBytes.Length; i++){sb.Append(hashBytes[i].ToString("x2"));}return sb.ToString();}}/// <summary>/// Post请求数据/// </summary>/// <param name="url"></param>/// <param name="appKey"></param>/// <param name="appSecret"></param>/// <param name="parameters"></param>/// <returns></returns>public static async Task<string> PostJsonAsync(string url, string appKey, string appSecret, Dictionary<string, object> obj){string requestBody = JsonConvert.SerializeObject(obj);Console.WriteLine($"原始数据: {requestBody}");// 生成随机的 IV（初始化向量）byte[] ivBytes = new byte[16];using (var rng = RandomNumberGenerator.Create()){rng.GetBytes(ivBytes);}string ivBase64 = Convert.ToBase64String(ivBytes);// 使用 SM4 进行加密（需要实现 SM4 加密算法）string codeData = EncryptSM4CBC(appSecret, requestBody, ivBytes);Console.WriteLine($"原始: {codeData}");var requestParam = new Dictionary<string, object>{{ "appKey", appKey },{ "version", "1" },{ "encryptStr", codeData }};foreach (var param in CreateCommonParam(appKey, appSecret, codeData, ivBase64)){requestParam.Add(param.Key, param.Value);}Console.WriteLine($"请求数据: {JsonConvert.SerializeObject(requestParam)}");using (var httpClient = new HttpClient()){var content = new StringContent(JsonConvert.SerializeObject(requestParam), Encoding.UTF8, "application/json");HttpResponseMessage response = await httpClient.PostAsync(url, content);string result = await response.Content.ReadAsStringAsync();Console.WriteLine(result);var ret = JsonConvert.DeserializeObject<Dictionary<string, object>>(result);if (ret.ContainsKey("data") && !string.IsNullOrEmpty(ret["data"]?.ToString())){string data = ret["data"].ToString();return DecryptSM4CBC(appSecret, data, ivBytes);}else{return result;}}}/// <summary>/// SM4 加密 CBC 模式/// </summary>/// <param name="key"></param>/// <param name="data"></param>/// <param name="iv"></param>/// <returns></returns>public static string EncryptSM4CBC(string key, string data, byte[] iv){byte[] keyBytes = Encoding.UTF8.GetBytes(key);byte[] dataBytes = Encoding.UTF8.GetBytes(data);// 应用 Zero PaddingdataBytes = ApplyZeroPadding(dataBytes, 16); // SM4 的块大小是 16 字节SM4Engine engine = new SM4Engine();CbcBlockCipher cipher = new CbcBlockCipher(engine);PaddedBufferedBlockCipher bufferedCipher = new PaddedBufferedBlockCipher(cipher);KeyParameter keyParam = new KeyParameter(keyBytes);ParametersWithIV keyParamWithIV = new ParametersWithIV(keyParam, iv);bufferedCipher.Init(true, keyParamWithIV);byte[] outputBytes = new byte[bufferedCipher.GetOutputSize(dataBytes.Length)];int length = bufferedCipher.ProcessBytes(dataBytes, 0, dataBytes.Length, outputBytes, 0);length += bufferedCipher.DoFinal(outputBytes, length);// 直接返回加密后的Base64字符串return Convert.ToBase64String(outputBytes, 0, length);}/// <summary>/// 自定义 Zero Padding 方法/// </summary>/// <param name="input"></param>/// <param name="blockSize"></param>/// <returns></returns>public static byte[] ApplyZeroPadding(byte[] input, int blockSize){int paddingLength = blockSize - (input.Length % blockSize);if (paddingLength == blockSize){return input; // 无需填充}byte[] paddedData = new byte[input.Length + paddingLength];Array.Copy(input, paddedData, input.Length);return paddedData;}/// <summary>/// SM4 解密 CBC 模式/// </summary>/// <param name="key"></param>/// <param name="encryptedData"></param>/// <param name="iv"></param>/// <returns></returns>public static string DecryptSM4CBC(string key, string encryptedData, byte[] iv){byte[] keyBytes = Encoding.UTF8.GetBytes(key);byte[] encryptedBytes = Convert.FromBase64String(encryptedData);// 应用 Zero PaddingencryptedBytes = ApplyZeroPadding(encryptedBytes, 16); // SM4 的块大小是 16 字节SM4Engine engine = new SM4Engine();CbcBlockCipher cipher = new CbcBlockCipher(engine);BufferedBlockCipher bufferedCipher = new BufferedBlockCipher(cipher);KeyParameter keyParam = new KeyParameter(keyBytes);ParametersWithIV keyParamWithIV = new ParametersWithIV(keyParam, iv);bufferedCipher.Init(false, keyParamWithIV);byte[] outputBytes = new byte[bufferedCipher.GetOutputSize(encryptedBytes.Length)];int length = bufferedCipher.ProcessBytes(encryptedBytes, 0, encryptedBytes.Length, outputBytes, 0);try{length += bufferedCipher.DoFinal(outputBytes, length);}catch (InvalidCipherTextException e){throw new Exception("解密失败：密文损坏或密钥/IV不正确", e);}return Encoding.UTF8.GetString(outputBytes, 0, length);}
}

当您遇到 Org.BouncyCastle.Crypto.InvalidCipherTextException: "pad block corrupted" 错误时，这通常意味着解密过程中，填充的块（pad block）不符合预期的格式或长度。

需要添加如下代码，指定填充方案

/// <summary>/// 自定义 Zero Padding 方法/// </summary>/// <param name="input"></param>/// <param name="blockSize"></param>/// <returns></returns>public static byte[] ApplyZeroPadding(byte[] input, int blockSize){int paddingLength = blockSize - (input.Length % blockSize);if (paddingLength == blockSize){return input; // 无需填充}byte[] paddedData = new byte[input.Length + paddingLength];Array.Copy(input, paddedData, input.Length);return paddedData;}

代码解析

自定义 Zero Padding:
- ApplyZeroPadding方法用于将数据填充到符合块大小（16字节）的倍数。
- 如果数据已经是块大小的倍数，则不进行填充。
加密过程:
- 创建一个SM4Engine实例，并将其包装在CbcBlockCipher中以使用CBC模式。
- 使用BufferedBlockCipher来处理加密操作。
- 使用提供的密钥和IV参数初始化加密器。
处理填充后的数据:
- 在加密之前，调用ApplyZeroPadding方法对数据进行零填充。
- 加密完成后，输出结果为Base64编码的字符串。