對於BouncyCastle類庫（包）來說，他提供了很多加密演算法，在與.net和java進行相互加解密過程中，得到了不錯的應用，本文以DES3為例，來說一下DES3加解密的過程。

加密過程

• 明文字元轉為byte陣列
• 對金鑰進行處理，處理後一般為16或者24位元組
• 對明文進行DES3加密，生成密文的byte陣列
• 對密文byte陣列進行base64的編碼

解密過程

• 對密文byte陣列進行base64的解碼
• 對金鑰進行處理，處理後一般為16或者24位元組
• 對解碼後的byte陣列進行DES3解密
• 對解密之後的byte陣列進行Encoding.UTF8.GetString方法的呼叫生成明文字串

原碼

 /// <summary>
  /// DES3加密
  /// https://www.go4expert.com/articles/bouncy-castle-net-implementation-triple-t24829/
  /// </summary>
  public class BouncyCastleHelper
  {
    static IBlockCipher engine = new DesEngine();

    /// <summary>
    /// 生成一個16位的key.
    /// </summary>
    /// <returns></returns>
    public string GenerateDES3Key()
    {
      CipherKeyGenerator cipherKeyGenerator = new CipherKeyGenerator();
      cipherKeyGenerator.Init(new KeyGenerationParameters(new SecureRandom(),192));
      //192 specifies the size of key in bits i.e 24 bytes 
      var keyDES3 = cipherKeyGenerator.GenerateKey();
      BigInteger bigInteger = new BigInteger(keyDES3);
      return bigInteger.ToString(16);
    }

    /// <summary>
    /// 做一個16位的md5加密，防止被其它人解析.
    /// </summary>
    /// <param name="Source"></param>
    /// <returns></returns>
    static byte[] GetMd5Digest(string Source)
    {
      var msgBytes = Encoding.UTF8.GetBytes(Source);
      var md5Digest = new MD5Digest();
      md5Digest.BlockUpdate(msgBytes,msgBytes.Length);
      byte[] result = new byte[md5Digest.GetDigestSize()];
      md5Digest.DoFinal(result,0);
      return result;
    }

    /// <summary>
    /// 使用DES3加密
    /// </summary>
    /// <param name="plainText">需要加密的字串</param>
    /// <param name="keys">加密字串的金鑰</param>
    /// <returns>加密後的字串</returns>
    public static string Encrypt(string plainText,string keys)
    {
      byte[] ptBytes = Encoding.UTF8.GetBytes(plainText);
      byte[] rv = Encrypt(ptBytes,keys);
      // 密文轉為base64字串 
      return Convert.ToBase64String(rv);
    }

    static byte[] Encrypt(byte[] ptBytes,string keys)
    {

      byte[] key = GetMd5Digest(keys);
      BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new DesEdeEngine());
      cipher.Init(true,new KeyParameter(key));
      byte[] rv = new byte[cipher.GetOutputSize(ptBytes.Length)];
      int tam = cipher.ProcessBytes(ptBytes,ptBytes.Length,rv,0);
      cipher.DoFinal(rv,tam);
      return rv;
    }

    /// <summary>
    /// 使用DES3解密
    /// </summary>
    /// <param name="cipherText">需要加密的字串</param>
    /// <param name="keys">加密字串的金鑰</param>
    /// <returns>解密後的字串</returns>
    public static string Decrypt(string cipherText,string keys)
    {
      // 把密文進行base64的解碼
      byte[] base64StringBytes = Convert.FromBase64String(cipherText);
      var rv = Decrypt(base64StringBytes,keys);
      // 字元陣列轉為明文字串
      return Encoding.UTF8.GetString(rv,rv.Length);
    }

    static byte[] Decrypt(byte[] cipherText,string keys)
    {
      byte[] key = GetMd5Digest(keys);
      BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new DesEdeEngine());
      cipher.Init(false,new KeyParameter(key));
      byte[] comparisonBytes = new byte[cipher.GetOutputSize(cipherText.Length)];
      int length = cipher.ProcessBytes(cipherText,comparisonBytes,0);
      cipher.DoFinal(comparisonBytes,length); //Do the final block
      return comparisonBytes;
    }
  }

呼叫

string result = BouncyCastleHelper.Encrypt("hello","abc123");
Console.WriteLine("hello=" + result);
Console.WriteLine("plainText=" + BouncyCastleHelper.Decrypt(result,"abc123"));

結果

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