SM2 是国家密码管理局组织制定并提出的椭圆曲线密码算法标准。

本文使用第三方密码库 BouncyCastle 实现 SM2 加解密，使用 NuGet 安装即可，包名：Portable.BouncyCastle，目前最新版本为：1.9.0。

using Org.BouncyCastle.Asn1.GM;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Generators;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Utilities.Encoders;
using System;
using System.Collections.Generic;
using System.Text;namespace AI_SXPA.Utility
{/// <summary>/// 可用/// </summary>public class Sm2Util{/// <summary>///     加密模式/// </summary>public enum Mode{C1C2C3,C1C3C2}private readonly Mode _mode;private readonly string _privkey;private ICipherParameters _privateKeyParameters;private string _pubkey;private ICipherParameters _publicKeyParameters;public Sm2Util(string pubkey, string privkey, Mode mode = Mode.C1C3C2, bool isPkcs8 = false){if (pubkey != null)_pubkey = pubkey;if (privkey != null)_privkey = privkey;_mode = mode;}public Sm2Util(string pubkey, Mode mode = Mode.C1C3C2, bool isPkcs8 = false){if (pubkey != null)_pubkey = pubkey;_mode = mode;}private ICipherParameters PrivateKeyParameters{get{try{var r = _privateKeyParameters;if (r == null)r = _privateKeyParameters =new ECPrivateKeyParameters(new BigInteger(_privkey, 16),new ECDomainParameters(GMNamedCurves.GetByName("SM2P256V1")));return r;}catch (Exception ex){return null;}}}private ICipherParameters PublicKeyParameters{get{try{var r = _publicKeyParameters;if (r == null){//截取64字节有效的SM2公钥（如果公钥首个字节为0x04）if (_pubkey.Length > 128) _pubkey = _pubkey.Substring(_pubkey.Length - 128);//将公钥拆分为x,y分量（各32字节）var stringX = _pubkey.Substring(0, 64);var stringY = _pubkey.Substring(stringX.Length);//将公钥x、y分量转换为BigInteger类型var x = new BigInteger(stringX, 16);var y = new BigInteger(stringY, 16);//通过公钥x、y分量创建椭圆曲线公钥规范var x9Ec = GMNamedCurves.GetByName("SM2P256V1");r = _publicKeyParameters = new ECPublicKeyParameters(x9Ec.Curve.CreatePoint(x, y),new ECDomainParameters(x9Ec));}return r;}catch (Exception ex){return null;}}}/// <summary>///     生成秘钥对/// </summary>/// <returns></returns>public static Dictionary<string, string> GenerateKeyPair(){string[] param ={"FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFF", // p,0"FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFC", // a,1"28E9FA9E9D9F5E344D5A9E4BCF6509A7F39789F515AB8F92DDBCBD414D940E93", // b,2"FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFF7203DF6B21C6052B53BBF40939D54123", // n,3"32C4AE2C1F1981195F9904466A39C9948FE30BBFF2660BE1715A4589334C74C7", // gx,4"BC3736A2F4F6779C59BDCEE36B692153D0A9877CC62A474002DF32E52139F0A0" // gy,5};var eccParam = param;var eccP = new BigInteger(eccParam[0], 16);var eccA = new BigInteger(eccParam[1], 16);var eccB = new BigInteger(eccParam[2], 16);var eccN = new BigInteger(eccParam[3], 16);var eccGx = new BigInteger(eccParam[4], 16);var eccGy = new BigInteger(eccParam[5], 16);ECFieldElement element = new FpFieldElement(eccP, eccGx);ECFieldElement ecFieldElement = new FpFieldElement(eccP, eccGy);ECCurve eccCurve = new FpCurve(eccP, eccA, eccB);ECPoint eccPointG = new FpPoint(eccCurve, element, ecFieldElement);var bcSpec = new ECDomainParameters(eccCurve, eccPointG, eccN);var ecgenparam = new ECKeyGenerationParameters(bcSpec, new SecureRandom());var generator = new ECKeyPairGenerator();generator.Init(ecgenparam);var key = generator.GenerateKeyPair();var ecpriv = (ECPrivateKeyParameters)key.Private;var ecpub = (ECPublicKeyParameters)key.Public;var privateKey = ecpriv.D;var publicKey = ecpub.Q;var dic = new Dictionary<string, string>();dic.Add("pubkey", Encoding.Default.GetString(Hex.Encode(publicKey.GetEncoded())));dic.Add("prikey", Encoding.Default.GetString(Hex.Encode(privateKey.ToByteArray())));//dic.Add("pubkey", Encoding.Default.GetString(Hex.Encode(publicKey.GetEncoded())).ToUpper());           //dic.Add("prikey", Encoding.Default.GetString(Hex.Encode(privateKey.ToByteArray())).ToUpper());return dic;}/// <summary>/// 解密/// </summary>/// <param name="data"></param>/// <returns></returns>public byte[] Decrypt(byte[] data){try{if (_mode == Mode.C1C3C2)data = C132ToC123(data);var sm2 = new SM2Engine(new SM3Digest());sm2.Init(false, PrivateKeyParameters);return sm2.ProcessBlock(data, 0, data.Length);}catch (Exception ex){return null;}}/// <summary>/// 加密/// </summary>/// <param name="data"></param>/// <returns></returns>public byte[] Encrypt(byte[] data){try{var sm2 = new SM2Engine(new SM3Digest());sm2.Init(true, new ParametersWithRandom(PublicKeyParameters));data = sm2.ProcessBlock(data, 0, data.Length);if (_mode == Mode.C1C3C2)data = C123ToC132(data);return data;}catch (Exception ex){return null;}}private static byte[] C123ToC132(byte[] c1c2c3){var gn = GMNamedCurves.GetByName("SM2P256V1");var c1Len = (gn.Curve.FieldSize + 7) / 8 * 2 + 1;var c3Len = 32;var result = new byte[c1c2c3.Length];Array.Copy(c1c2c3, 0, result, 0, c1Len); //c1Array.Copy(c1c2c3, c1c2c3.Length - c3Len, result, c1Len, c3Len); //c3Array.Copy(c1c2c3, c1Len, result, c1Len + c3Len, c1c2c3.Length - c1Len - c3Len); //c2return result;}private static byte[] C132ToC123(byte[] c1c3c2){var gn = GMNamedCurves.GetByName("SM2P256V1");var c1Len = (gn.Curve.FieldSize + 7) / 8 * 2 + 1;var c3Len = 32;var result = new byte[c1c3c2.Length];Array.Copy(c1c3c2, 0, result, 0, c1Len); //c1: 0->65Array.Copy(c1c3c2, c1Len + c3Len, result, c1Len, c1c3c2.Length - c1Len - c3Len); //c2Array.Copy(c1c3c2, c1Len, result, c1c3c2.Length - c3Len, c3Len); //c3return result;}/// <summary>///     字节数组转16进制原码字符串/// </summary>/// <param name="bytes"></param>/// <returns></returns>public static string BytesToHexStr(byte[] bytes){var str = "";if (bytes != null)for (var i = 0; i < bytes.Length; i++)str += bytes[i].ToString("X2");return str;}/// <summary>///     16进制原码字符串转字节数组/// </summary>/// <param name="hexStr">"AABBCC"或"AA BB CC"格式的字符串</param>/// <returns></returns>public static byte[] HexStrToBytes(string hexStr){hexStr = hexStr.Replace(" ", "");if (hexStr.Length % 2 != 0) throw new ArgumentException("参数长度不正确,必须是偶数位。");var bytes = new byte[hexStr.Length / 2];for (var i = 0; i < bytes.Length; i++){var b = Convert.ToByte(hexStr.Substring(i * 2, 2), 16);bytes[i] = b;}return bytes;}}
}

SM2 加解密联调时踩坑
1、密文数据，有些加密硬件出来密文结构为 C1|C2|C3 ，有些为 C1|C3|C2 , 需要对应密文结构做解密操作
2、有些加密硬件，公钥前加04 ，私钥前加00，密文前加04 ，在处理时候，可以根据长度处理，尤其 04 的处理。

在线验证：在线SM2加密解密,生成公钥/私钥对 (config.net.cn)