C# SM2（国密2）示例代码

以下是一个简单的 C# SM2（国密2）示例代码：

using System;
using System.Security.Cryptography;

namespace SM2Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            string plainText = "Hello, SM2!"; // 待加密明文

            using (var sm2 = new SM2CryptoServiceProvider())
            {
                var publicKey = sm2.ExportCspBlob(false); // 获取公钥
                var privateKey = sm2.ExportCspBlob(true); // 获取私钥

                var encryptedData = sm2.Encrypt(Encoding.UTF8.GetBytes(plainText)); // 加密
                var decryptedData = sm2.Decrypt(encryptedData); // 解密

                Console.WriteLine("Plain text: " + plainText);
                Console.WriteLine("Encrypted data: " + Convert.ToBase64String(encryptedData));
                Console.WriteLine("Decrypted data: " + Encoding.UTF8.GetString(decryptedData));
            }
        }
    }

    class SM2CryptoServiceProvider : ECDsa
    {
        private readonly CngKey _cngKey;

        public SM2CryptoServiceProvider()
        {
            _cngKey = CngKey.Create(CngAlgorithm.ECDsaP256, null, new CngKeyCreationParameters
            {
                ExportPolicy = CngExportPolicies.AllowPlaintextExport
            });
        }

        public override void ImportParameters(ECParameters parameters)
        {
            _cngKey.ImportParameters(parameters);
        }

        public override ECParameters ExportParameters(bool includePrivateParameters)
        {
            return _cngKey.ExportParameters(includePrivateParameters);
        }

        public override byte[] SignData(byte[] data)
        {
            throw new NotSupportedException();
        }

        public override bool VerifyData(byte[] data, byte[] signature)
        {
            throw new NotSupportedException();
        }

        public override byte[] Encrypt(byte[] plaintext)
        {
            using (var provider = new ECDiffieHellmanCng(_cngKey))
            {
                var publicKey = provider.PublicKey.ToByteArray();
                var sharedSecret = provider.DeriveKeyMaterial(CngKey.Import(publicKey, CngKeyBlobFormat.EccPublicBlob));
                var encryptedData = SM2Utils.Encrypt(plaintext, publicKey, sharedSecret);
                return encryptedData;
            }
        }

        public override byte[] Decrypt(byte[] ciphertext)
        {
            using (var provider = new ECDiffieHellmanCng(_cngKey))
            {
                var publicKey = provider.PublicKey.ToByteArray();
                var sharedSecret = provider.DeriveKeyMaterial(CngKey.Import(publicKey, CngKeyBlobFormat.EccPublicBlob));
                var decryptedData = SM2Utils.Decrypt(ciphertext, publicKey, sharedSecret);
                return decryptedData;
            }
        }
    }

    static class SM2Utils
    {
        public static byte[] Encrypt(byte[] plaintext, byte[] publicKey, byte[] sharedSecret)
        {
            var cipher = new SM2Cipher();
            cipher.Init(true, new SM2Parameters(publicKey));
            var encryptedData = cipher.DoFinal(plaintext, sharedSecret);
            return encryptedData;
        }

        public static byte[] Decrypt(byte[] ciphertext, byte[] publicKey, byte[] sharedSecret)
        {
            var cipher = new SM2Cipher();
            cipher.Init(false, new SM2Parameters(publicKey));
            var decryptedData = cipher.DoFinal(ciphertext, sharedSecret);
            return decryptedData;
        }
    }

    class SM2Cipher
    {
        private readonly SM2Engine _engine;

        public SM2Cipher()
        {
            _engine = new SM2Engine();
        }

        public void Init(bool forEncryption, SM2Parameters parameters)
        {
            _engine.Init(forEncryption, parameters);
        }

        public byte[] DoFinal(byte[] input, byte[] sharedSecret)
        {
            var kdf = new SM2KdfBytesGenerator(new Sha256Digest());
            kdf.Init(sharedSecret, null);
            var key = new KeyParameter(kdf.GenerateBytes(32));

            var cipher = new PaddedBufferedBlockCipher(_engine);
            cipher.Init(forEncryption: true, key);

            var output = new byte[cipher.GetOutputSize(input.Length)];
            var outputLength = cipher.ProcessBytes(input, output, outputOffset: 0);
            outputLength += cipher.DoFinal(output, outputLength);

            var result = new byte[outputLength];
            Array.Copy(output, result, outputLength);

            return result;
        }
    }

    class SM2KdfBytesGenerator : Kdf1BytesGenerator
    {
        private static readonly byte[] _zValue = { 0x00 };

        public SM2KdfBytesGenerator(IDigest digest) : base(digest)
        {
        }

        public override int GenerateBytes(byte[] output, int outOff, int length)
        {
            var counter = 1;
            var v = new byte[Digest.GetDigestSize()];

            var outputOffset = outOff;
            var outputRemaining = length;

            while (outputRemaining > 0)
            {
                Digest.BlockUpdate(_zValue, 0, _zValue.Length);
                Digest.Update((byte)(counter >> 24));
                Digest.Update((byte)(counter >> 16));
                Digest.Update((byte)(counter >> 8));
                Digest.Update((byte)(counter));

                Digest.DoFinal(v, 0);

                var chunkLength = Math.Min(outputRemaining, v.Length);
                Array.Copy(v, 0, output, outputOffset, chunkLength);

                outputOffset += chunkLength;
                outputRemaining -= chunkLength;
                counter++;
            }

            return length;
        }
    }

    class SM2Parameters : ICipherParameters
    {
        public byte[] PublicKey { get; }

        public SM2Parameters(byte[] publicKey)
        {
            PublicKey = publicKey;
        }
    }
}

此示例代码中使用了 Bouncy Castle 库实现 SM2 加密和解密，可以通过 NuGet 安装。