C#里的一些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>
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