最近收到了很多朋友的來信說希望提供DES的C#代碼，但是我個人認為，.NET 提供了很多標准函數，沒有必要自己寫，所以我也只發布了C++的代碼，如果大家一定要熟悉加密過程的話，也可以自己動手實現整個過程，這個可以參考我博客裡的DES 算法介紹，和yxyDES2 Class的代碼，代碼注釋相當的清楚。
.NET 提供了很多標准加密、解密函數，我簡要介紹一下DES，SHA1，RSA的標准函數的使用。如果你想做一個網絡安全模塊，只需將三種算法結合起來設計一個模型，我相信可以實現很多復雜的功能。
示例本身並不復雜，我也不做過多解釋，我也學Linus Torvalds一樣吼一句："Read the f**ing code”，哈哈，開個玩笑，我相信大家肯定能看懂。
注：以下示例需引用命名空間 ： using System.Security.Cryptography;
一. DES 加密、解密
我相信一下注釋相當清楚了，加上我博客裡關於DES的文章確實不少，所以DES不做任何解釋，怎麼調用就更不用解釋了吧，呵呵：
//默認密鑰向量
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">加密密鑰,要求為8位</param>
/// <returns>加密成功返回加密後的字符串，失敗返回源串</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">解密密鑰,要求為8位,和加密密鑰相同</param>
/// <returns>解密成功返回解密後的字符串，失敗返源串</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算法沒有解密）
安全哈希算法（Secure Hash Algorithm）主要適用於數字簽名標准（Digital Signature Standard DSS）裡面定義的數字簽名算法（Digital Signature Algorithm DSA）。對於長度小於2^64位的消息，SHA1會產生一個160位的消息摘要。當接收到消息的時候，這個消息摘要可以用來驗證數據的完整性。在傳輸的過程中，數據很可能會發生變化，那麼這時候就會產生不同的消息摘要。
SHA1有如下特性：不可以從消息摘要中復原信息；兩個不同的消息不會產生同樣的消息摘要。
代碼如下：
/// <summary>
/// use sha1 to encrypt string
/// </summary>
public string SHA1_Encrypt(string Source_String)
{
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 （本例來自 MSDN）
RSA加密算法是一種非對稱加密算法。在公鑰加密標准和電子商業中RSA被廣泛使用。RSA是1977年由羅納德·李維斯特（Ron Rivest）、阿迪·薩莫爾（Adi Shamir）和倫納德·阿德曼（Leonard Adleman）一起提出的。當時他們三人都在麻省理工學院工作。RSA就是他們三人姓氏開頭字母拼在一起組成的。
RSA算法的可靠性基於分解極大的整數是很困難的。假如有人找到一種很快的分解因子的算法的話，那麼用RSA加密的信息的可靠性就肯定會極度下降。但找到這樣的算法的可能性是非常小的。今天只有短的RSA鑰匙才可能被強力方式解破。到2008年為止，世界上還沒有任何可靠的攻擊RSA算法的方式。只要其鑰匙的長度足夠長，用RSA加密的信息實際上是不能被解破的。
具體算法過程請參考http://zh.wikipedia.org/wiki/RSA%E5%8A%A0%E5%AF%86%E6%BC%94%E7%AE%97%E6%B3%95
代碼示例如下（來自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
