学步园

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<br /> private byte[] Keys = { 0xEF, 0xAB, 0x56, 0x78, 0x90, 0x34, 0xCD, 0x12 };<br /> /// <summary><br /> /// DES加密字符串<br /> /// </summary><br /> /// <param name="encryptString">待加密的字符串</param><br /> /// <param name="encryptKey">加密密钥,要求为8位</param><br /> /// <returns>加密成功返回加密后的字符串，失败返回源串</returns><br /> public string EncryptDES(string encryptString, string encryptKey)<br /> {<br /> try<br /> {<br /> byte[] rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));<br /> byte[] rgbIV = Keys;<br /> byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptString);<br /> DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider();<br /> MemoryStream mStream = new MemoryStream();<br /> CryptoStream cStream = new CryptoStream(mStream, dCSP.CreateEncryptor(rgbKey, rgbIV), CryptoStreamMode.Write);<br /> cStream.Write(inputByteArray, 0, inputByteArray.Length);<br /> cStream.FlushFinalBlock();<br /> return Convert.ToBase64String(mStream.ToArray());<br /> }<br /> catch<br /> {<br /> return encryptString;<br /> }<br /> }</p> <p> /// <summary><br /> /// DES解密字符串<br /> /// </summary><br /> /// <param name="decryptString">待解密的字符串</param><br /> /// <param name="decryptKey">解密密钥,要求为8位,和加密密钥相同</param><br /> /// <returns>解密成功返回解密后的字符串，失败返源串</returns><br /> public string DecryptDES(string decryptString, string decryptKey)<br /> {<br /> try<br /> {<br /> byte[] rgbKey = Encoding.UTF8.GetBytes(decryptKey.Substring(0, 8));<br /> byte[] rgbIV = Keys;<br /> byte[] inputByteArray = Convert.FromBase64String(decryptString);<br /> DESCryptoServiceProvider DCSP = new DESCryptoServiceProvider();<br /> MemoryStream mStream = new MemoryStream();<br /> CryptoStream cStream = new CryptoStream(mStream, DCSP.CreateDecryptor(rgbKey, rgbIV), CryptoStreamMode.Write);<br /> cStream.Write(inputByteArray, 0, inputByteArray.Length);<br /> cStream.FlushFinalBlock();<br /> return Encoding.UTF8.GetString(mStream.ToArray());<br /> }<br /> catch<br /> {<br /> return decryptString;<br /> }<br /> }<br />

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><br /> /// use sha1 to encrypt string<br /> /// </summary><br /> public string SHA1_Encrypt(string Source_String)<br /> {<br /> byte[] StrRes = Encoding.Default.GetBytes(Source_String);<br /> HashAlgorithm iSHA = new SHA1CryptoServiceProvider();<br /> StrRes = iSHA.ComputeHash(StrRes);<br /> StringBuilder EnText = new StringBuilder();<br /> foreach (byte iByte in StrRes)<br /> {<br /> EnText.AppendFormat("{0:x2}", iByte);<br /> }<br /> return EnText.ToString();<br /> }<br />

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;<br /> using System.Security.Cryptography;<br /> using System.IO;<br /> using System.Text;</p> <p>namespace Microsoft.Samples.Security.PublicKey<br /> {<br /> class App<br /> {<br /> // Main entry point<br /> static void Main(string[] args)<br /> {<br /> // Instantiate 3 People for example. See the Person class below<br /> Person alice = new Person("Alice");<br /> Person bob = new Person("Bob");<br /> Person steve = new Person("Steve");</p> <p> // Messages that will exchanged. See CipherMessage class below<br /> CipherMessage aliceMessage;<br /> CipherMessage bobMessage;<br /> CipherMessage steveMessage;</p> <p> // Example of encrypting/decrypting your own message<br /> Console.WriteLine("Encrypting/Decrypting Your Own Message");<br /> Console.WriteLine("-----------------------------------------");</p> <p> // Alice encrypts a message using her own public key<br /> aliceMessage = alice.EncryptMessage("Alice wrote this message");<br /> // then using her private key can decrypt the message<br /> alice.DecryptMessage(aliceMessage);<br /> // Example of Exchanging Keys and Messages<br /> Console.WriteLine();<br /> Console.WriteLine("Exchanging Keys and Messages");<br /> Console.WriteLine("-----------------------------------------");</p> <p> // Alice Sends a copy of her public key to Bob and Steve<br /> bob.GetPublicKey(alice);<br /> steve.GetPublicKey(alice);</p> <p> // Bob and Steve both encrypt messages to send to Alice<br /> bobMessage = bob.EncryptMessage("Hi Alice! - Bob.");<br /> steveMessage = steve.EncryptMessage("How are you? - Steve");</p> <p> // Alice can decrypt and read both messages<br /> alice.DecryptMessage(bobMessage);<br /> alice.DecryptMessage(steveMessage);</p> <p> Console.WriteLine();<br /> Console.WriteLine("Private Key required to read the messages");<br /> Console.WriteLine("-----------------------------------------");</p> <p> // Steve cannot read the message that Bob encrypted<br /> steve.DecryptMessage(bobMessage);<br /> // Not even Bob can use the Message he encrypted for Alice.<br /> // The RSA private key is required to decrypt the RS2 key used<br /> // in the decryption.<br /> bob.DecryptMessage(bobMessage);</p> <p> } // method Main<br /> } // class App</p> <p> class CipherMessage<br /> {<br /> public byte[] cipherBytes; // RC2 encrypted message text<br /> public byte[] rc2Key; // RSA encrypted rc2 key<br /> public byte[] rc2IV; // RC2 initialization vector<br /> }</p> <p> class Person<br /> {<br /> private RSACryptoServiceProvider rsa;<br /> private RC2CryptoServiceProvider rc2;<br /> private string name;</p> <p> // Maximum key size for the RC2 algorithm<br /> const int keySize = 128;</p> <p> // Person constructor<br /> public Person(string p_Name)<br /> {<br /> rsa = new RSACryptoServiceProvider();<br /> rc2 = new RC2CryptoServiceProvider();<br /> rc2.KeySize = keySize;<br /> name = p_Name;<br /> }</p> <p> // Used to send the rsa public key parameters<br /> public RSAParameters SendPublicKey()<br /> {<br /> RSAParameters result = new RSAParameters();<br /> try<br /> {<br /> result = rsa.ExportParameters(false);<br /> }<br /> catch (CryptographicException e)<br /> {<br /> Console.WriteLine(e.Message);<br /> }<br /> return result;<br /> }</p> <p> // Used to import the rsa public key parameters<br /> public void GetPublicKey(Person receiver)<br /> {<br /> try<br /> {<br /> rsa.ImportParameters(receiver.SendPublicKey());<br /> }<br /> catch (CryptographicException e)<br /> {<br /> Console.WriteLine(e.Message);<br /> }<br /> }</p> <p> public CipherMessage EncryptMessage(string text)<br /> {<br /> // Convert string to a byte array<br /> CipherMessage message = new CipherMessage();<br /> byte[] plainBytes = Encoding.Unicode.GetBytes(text.ToCharArray());</p> <p> // A new key and iv are generated for every message<br /> rc2.GenerateKey();<br /> rc2.GenerateIV();</p> <p> // The rc2 initialization doesnt need to be encrypted, but will<br /> // be used in conjunction with the key to decrypt the message.<br /> message.rc2IV = rc2.IV;<br /> try<br /> {<br /> // Encrypt the RC2 key using RSA encryption<br /> message.rc2Key = rsa.Encrypt(rc2.Key, false);<br /> }<br /> catch (CryptographicException e)<br /> {<br /> // The High Encryption Pack is required to run this sample<br /> // because we are using a 128-bit key. See the readme for<br /> // additional information.<br /> Console.WriteLine("Encryption Failed. Ensure that the" +<br /> " High Encryption Pack is installed.");<br /> Console.WriteLine("Error Message: " + e.Message);<br /> Environment.Exit(0);<br /> }<br /> // Encrypt the Text Message using RC2 (Symmetric algorithm)<br /> ICryptoTransform sse = rc2.CreateEncryptor();<br /> MemoryStream ms = new MemoryStream();<br /> CryptoStream cs = new CryptoStream(ms, sse, CryptoStreamMode.Write);<br /> try<br /> {<br /> cs.Write(plainBytes, 0, plainBytes.Length);<br /> cs.FlushFinalBlock();<br /> message.cipherBytes = ms.ToArray();<br /> }<br /> catch (Exception e)<br /> {<br /> Console.WriteLine(e.Message);<br /> }<br /> finally<br /> {<br /> ms.Close();<br /> cs.Close();<br /> }<br /> return message;<br /> } // method EncryptMessage</p> <p> public void DecryptMessage(CipherMessage message)<br /> {<br /> // Get the RC2 Key and Initialization Vector<br /> rc2.IV = message.rc2IV;<br /> try<br /> {<br /> // Try decrypting the rc2 key<br /> rc2.Key = rsa.Decrypt(message.rc2Key, false);<br /> }<br /> catch (CryptographicException e)<br /> {<br /> Console.WriteLine("Decryption Failed: " + e.Message);<br /> return;<br /> }</p> <p> ICryptoTransform ssd = rc2.CreateDecryptor();<br /> // Put the encrypted message in a memorystream<br /> MemoryStream ms = new MemoryStream(message.cipherBytes);<br /> // the CryptoStream will read cipher text from the MemoryStream<br /> CryptoStream cs = new CryptoStream(ms, ssd, CryptoStreamMode.Read);<br /> byte[] initialText = new Byte[message.cipherBytes.Length];</p> <p> try<br /> {<br /> // Decrypt the message and store in byte array<br /> cs.Read(initialText, 0, initialText.Length);<br /> }<br /> catch (Exception e)<br /> {<br /> Console.WriteLine(e.Message);<br /> }<br /> finally<br /> {<br /> ms.Close();<br /> cs.Close();<br /> }</p> <p> // Display the message received<br /> Console.WriteLine(name + " received the following message:");<br /> Console.WriteLine(" " + Encoding.Unicode.GetString(initialText));<br /> } // method DecryptMessage<br /> } // class Person<br /> } // namespace PublicKey<br />