C#中加密解密标准函数示例——DES，SHA1，RSA

最近收到了很多朋友的来信说希望提供DES的C#代码，但是我个人认为，.NET 提供了很多标准函数，没有必要自己写，所以我也只发布了C++的代码，如果大家一定要熟悉加密过程的话，也可以自己动手实现整个过程，这个可以参考我博客里的DES 算法介绍，和yxyDES2 Class的代码，代码注释相当的清楚。

　　.NET 提供了很多标准加密、解密函数，我简要介绍一下DES，SHA1，RSA的标准函数的使用。如果你想做一个网络安全模块，只需将三种算法结合起来设计一个模型，我相信可以实现很多复杂的功能。
　　示例本身并不复杂，我也不做过多解释，我也学Linus Torvalds一样吼一句："Read the f**ing code”，哈哈，开个玩笑，我相信大家肯定能看懂。

注：以下示例需引用命名空间 ： using System.Security.Cryptography;

一. DES 加密、解密
　　我相信一下注释相当清楚了，加上我博客里关于DES的文章确实不少，所以DES不做任何解释，怎么调用就更不用解释了吧，呵呵：

//默认密钥向量
        private byte Keys = { 0xEF, 0xAB, 0x56, 0x78, 0x90, 0x34, 0xCD, 0x12 };
        /**//// <summary>
        /// DES加密字符串
        /// </summary>
        /// <param name="encryptString">待加密的字符串</param>
        /// <param name="encryptKey">加密密钥,要求为8位</param>
        /// <returns>加密成功返回加密后的字符串，失败返回源串</returns>
        public string EncryptDES(string encryptString, string encryptKey)
        {
            try
            {
                byte rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));
                byte rgbIV = Keys;
                byte inputByteArray = Encoding.UTF8.GetBytes(encryptString);
                DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider();
                MemoryStream mStream = new MemoryStream();
                CryptoStream cStream = new CryptoStream(mStream, dCSP.CreateEncryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                cStream.Write(inputByteArray, 0, inputByteArray.Length);
                cStream.FlushFinalBlock();
                return Convert.ToBase64String(mStream.ToArray());
            }
            catch
            {
                return encryptString;
            }
        }

        /**//// <summary>
        /// DES解密字符串
        /// </summary>
        /// <param name="decryptString">待解密的字符串</param>
        /// <param name="decryptKey">解密密钥,要求为8位,和加密密钥相同</param>
        /// <returns>解密成功返回解密后的字符串，失败返源串</returns>
        public string DecryptDES(string decryptString, string decryptKey)
        {
            try
            {
                byte rgbKey = Encoding.UTF8.GetBytes(decryptKey.Substring(0, 8));
                byte rgbIV = Keys;
                byte inputByteArray = Convert.FromBase64String(decryptString);
                DESCryptoServiceProvider DCSP = new DESCryptoServiceProvider();
                MemoryStream mStream = new MemoryStream();
                CryptoStream cStream = new CryptoStream(mStream, DCSP.CreateDecryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                cStream.Write(inputByteArray, 0, inputByteArray.Length);
                cStream.FlushFinalBlock();
                return Encoding.UTF8.GetString(mStream.ToArray());
            }
            catch
            {
                return decryptString;
            }
        }

二. SHA1 加密 （HASH算法没有解密）

　　安全哈希算法（Secure Hash Algorithm）主要适用于数字签名标准（Digital Signature Standard DSS）里面定义的数字签名算法（Digital Signature Algorithm DSA）。对于长度小于2^64位的消息，SHA1会产生一个160位的消息摘要。当接收到消息的时候，这个消息摘要可以用来验证数据的完整性。在传输的过程中，数据很可能会发生变化，那么这时候就会产生不同的消息摘要。
SHA1有如下特性：不可以从消息摘要中复原信息；两个不同的消息不会产生同样的消息摘要。

代码如下：

/// <summary>
        /// use sha1 to encrypt string
        /// </summary>

{
            byte StrRes = Encoding.Default.GetBytes(Source_String);
            HashAlgorithm iSHA = new SHA1CryptoServiceProvider();
            StrRes = iSHA.ComputeHash(StrRes);
            StringBuilder EnText = new StringBuilder();
            foreach (byte iByte in StrRes)
            {
                EnText.AppendFormat("{0:x2}", iByte);
            }
            return EnText.ToString();
        }

三.RSA 加密、解密 （本例来自 MSDN）
　　RSA加密算法是一种非对称加密算法。在公钥加密标准和电子商业中RSA被广泛使用。RSA是1977年由罗纳德·李维斯特（Ron Rivest）、阿迪·萨莫尔（Adi Shamir）和伦纳德·阿德曼（Leonard Adleman）一起提出的。当时他们三人都在麻省理工学院工作。RSA就是他们三人姓氏开头字母拼在一起组成的。
　　RSA算法的可靠性基于分解极大的整数是很困难的。假如有人找到一种很快的分解因子的算法的话，那么用RSA加密的信息的可靠性就肯定会极度下降。但找到这样的算法的可能性是非常小的。今天只有短的RSA钥匙才可能被强力方式解破。到2008年为止，世界上还没有任何可靠的攻击RSA算法的方式。只要其钥匙的长度足够长，用RSA加密的信息实际上是不能被解破的。
　　具体算法过程请参考http://zh.wikipedia.org/wiki/RSA%E5%8A%A0%E5%AF%86%E6%BC%94%E7%AE%97%E6%B3%95
　　代码示例如下（来自MSDN）：

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

namespace Microsoft.Samples.Security.PublicKey
{
  class App
  {
    // Main entry point
    static void Main(string args)
    {
      // Instantiate 3 People for example. See the Person class below
      Person alice = new Person("Alice");
      Person bob = new Person("Bob");
      Person steve = new Person("Steve");

      // Messages that will exchanged. See CipherMessage class below
      CipherMessage aliceMessage;
      CipherMessage bobMessage;
      CipherMessage steveMessage;

      // Example of encrypting/decrypting your own message
      Console.WriteLine("Encrypting/Decrypting Your Own Message");
      Console.WriteLine("-----------------------------------------");

      // Alice encrypts a message using her own public key
      aliceMessage = alice.EncryptMessage("Alice wrote this message");
      // then using her private key can decrypt the message
      alice.DecryptMessage(aliceMessage);
      // Example of Exchanging Keys and Messages
      Console.WriteLine();
      Console.WriteLine("Exchanging Keys and Messages");
      Console.WriteLine("-----------------------------------------");

      // Alice Sends a copy of her public key to Bob and Steve
      bob.GetPublicKey(alice);
      steve.GetPublicKey(alice);

      // Bob and Steve both encrypt messages to send to Alice
      bobMessage = bob.EncryptMessage("Hi Alice! - Bob.");
      steveMessage = steve.EncryptMessage("How are you? - Steve");

      // Alice can decrypt and read both messages
      alice.DecryptMessage(bobMessage);
      alice.DecryptMessage(steveMessage);

      Console.WriteLine();
      Console.WriteLine("Private Key required to read the messages");
      Console.WriteLine("-----------------------------------------");

      // Steve cannot read the message that Bob encrypted
      steve.DecryptMessage(bobMessage);
      // Not even Bob can use the Message he encrypted for Alice.
      // The RSA private key is required to decrypt the RS2 key used
      // in the decryption.
      bob.DecryptMessage(bobMessage);

    } // method Main
  } // class App

  class CipherMessage
  {
    public byte cipherBytes;  // RC2 encrypted message text
    public byte rc2Key;       // RSA encrypted rc2 key
    public byte rc2IV;        // RC2 initialization vector
  }

  class Person
  {
    private RSACryptoServiceProvider rsa;
    private RC2CryptoServiceProvider rc2;
    private string name;

    // Maximum key size for the RC2 algorithm
    const int keySize = 128;

    // Person constructor
    public Person(string p_Name)
    {
      rsa = new RSACryptoServiceProvider();
      rc2 = new RC2CryptoServiceProvider();
      rc2.KeySize = keySize;
      name = p_Name;
    }

    // Used to send the rsa public key parameters
    public RSAParameters SendPublicKey()  
    {
      RSAParameters result = new RSAParameters();
      try  
      {
        result = rsa.ExportParameters(false);
      }
      catch (CryptographicException e)
      {
        Console.WriteLine(e.Message);
      }
      return result;
    }

    // Used to import the rsa public key parameters
    public void GetPublicKey(Person receiver)
    {
      try  
      {
        rsa.ImportParameters(receiver.SendPublicKey());  
      }
      catch (CryptographicException e)
      {
        Console.WriteLine(e.Message);
      }
    }

    public CipherMessage EncryptMessage(string text)
    {
      // Convert string to a byte array
      CipherMessage message = new CipherMessage();
      byte plainBytes = Encoding.Unicode.GetBytes(text.ToCharArray());

      // A new key and iv are generated for every message
      rc2.GenerateKey();
      rc2.GenerateIV();

      // The rc2 initialization doesnt need to be encrypted, but will
      // be used in conjunction with the key to decrypt the message.
      message.rc2IV = rc2.IV;
      try  
      {
        // Encrypt the RC2 key using RSA encryption
        message.rc2Key = rsa.Encrypt(rc2.Key, false);
      }
      catch (CryptographicException e)
      {
        // The High Encryption Pack is required to run this  sample
        // because we are using a 128-bit key. See the readme for
        // additional information.
        Console.WriteLine("Encryption Failed. Ensure that the" +  
          " High Encryption Pack is installed.");
        Console.WriteLine("Error Message: " + e.Message);
        Environment.Exit(0);
      }
      // Encrypt the Text Message using RC2 (Symmetric algorithm)
      ICryptoTransform sse = rc2.CreateEncryptor();
      MemoryStream ms = new MemoryStream();
      CryptoStream cs = new CryptoStream(ms, sse, CryptoStreamMode.Write);
      try
      {
          cs.Write(plainBytes, 0, plainBytes.Length);
          cs.FlushFinalBlock();
          message.cipherBytes = ms.ToArray();
      }
      catch (Exception e)
      {
          Console.WriteLine(e.Message);
      }      
      finally
      {
        ms.Close();
        cs.Close();
      }
      return message;
    } // method EncryptMessage


    public void DecryptMessage(CipherMessage message)
    {
      // Get the RC2 Key and Initialization Vector
      rc2.IV = message.rc2IV;
      try  
      {
        // Try decrypting the rc2 key
        rc2.Key = rsa.Decrypt(message.rc2Key, false);
      }
      catch (CryptographicException e)
      {
        Console.WriteLine("Decryption Failed: " + e.Message);
        return;
      }
      
      ICryptoTransform ssd = rc2.CreateDecryptor();
      // Put the encrypted message in a memorystream
      MemoryStream ms = new MemoryStream(message.cipherBytes);
      // the CryptoStream will read cipher text from the MemoryStream
      CryptoStream cs = new CryptoStream(ms, ssd, CryptoStreamMode.Read);
      byte initialText = new Byte[message.cipherBytes.Length];

      try
      {
          // Decrypt the message and store in byte array
          cs.Read(initialText, 0, initialText.Length);
      }
      catch (Exception e)
      {
          Console.WriteLine(e.Message);
      }      
      finally  
      {
        ms.Close();
        cs.Close();
      }

      // Display the message received
      Console.WriteLine(name + " received the following message:");
      Console.WriteLine("  " + Encoding.Unicode.GetString(initialText));
    } // method DecryptMessage
  } // class Person
} // namespace PublicKey