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。.Net的推出，我们能够利用.Net Framework中的类提供的加密服务来保证数据安全。目前应用较为广泛的加密方法是使用RSA算法进行加密。在.Net Framework中与RSA加密算法相关的类主要有两个：RSA 类和RSACryptoServiceProvider 类。按照MSDN的说法RSA 类是“表示 RSA 算法的所有实现均从中继承的基类”，而RSACryptoServiceProvider 类是“使用加密服务提供程序 (CSP) 提供的 RSA 算法的实现执行不对称加密和解密”。另外，“表示 RSA 算法的标准参数”的RSAParameters 结构也是很重要的，它保存了RSA算法的参数。
这里具体讲述一下在C#中如何使用框架提供的RSA算法来对我们的信息加密、签名、验证签名、解密的这个几个步骤的实现
using System.Security.Cryptography;
using System.Management;
using Microsoft.Win32;
/// <summary>
/// 生成公私钥
/// </summary>
/// <param name="PrivateKeyPath"></param>
/// <param name="PublicKeyPath"></param>
public void RSAKey(string PrivateKeyPath, string PublicKeyPath)
{
try
{
RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
this.CreatePrivateKeyXML(PrivateKeyPath, provider.ToXmlString(true));
this.CreatePublicKeyXML(PublicKeyPath, provider.ToXmlString(false));
}
catch (Exception exception)
{
throw exception;
}
}
/// <summary>
/// 对原始数据进行MD5加密
/// </summary>
/// <param name="m_strSource">待加密数据</param>
/// <returns>返回机密后的数据</returns>
public string GetHash(string m_strSource)
{
HashAlgorithm algorithm = HashAlgorithm.Create("MD5");
byte[] bytes = Encoding.GetEncoding("GB2312").GetBytes(m_strSource);
byte[] inArray = algorithm.ComputeHash(bytes);
return Convert.ToBase64String(inArray);
}
/// <summary>
/// RSA加密
/// </summary>
/// <param name="xmlPublicKey">公钥</param>
/// <param name="m_strEncryptString">MD5加密后的数据</param>
/// <returns>RSA公钥加密后的数据</returns>
public string RSAEncrypt(string xmlPublicKey, string m_strEncryptString)
{
string str2;
try
{
RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
provider.FromXmlString(xmlPublicKey);
byte[] bytes = new UnicodeEncoding().GetBytes(m_strEncryptString);
str2 = Convert.ToBase64String(provider.Encrypt(bytes, false));
}
catch (Exception exception)
{
throw exception;
}
return str2;
}
/// <summary>
/// RSA解密
/// </summary>
/// <param name="xmlPrivateKey">私钥</param>
/// <param name="m_strDecryptString">待解密的数据</param>
/// <returns>解密后的结果</returns>
public string RSADecrypt(string xmlPrivateKey, string m_strDecryptString)
{
string str2;
try
{
RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
provider.FromXmlString(xmlPrivateKey);
byte[] rgb = Convert.FromBase64String(m_strDecryptString);
byte[] buffer2 = provider.Decrypt(rgb, false);
str2 = new UnicodeEncoding().GetString(buffer2);
}
catch (Exception exception)
{
throw exception;
}
return str2;
}
/// <summary>
/// 对MD5加密后的密文进行签名
/// </summary>
/// <param name="p_strKeyPrivate">私钥</param>
/// <param name="m_strHashbyteSignature">MD5加密后的密文</param>
/// <returns></returns>
public string SignatureFormatter(string p_strKeyPrivate, string m_strHashbyteSignature)
{
byte[] rgbHash = Convert.FromBase64String(m_strHashbyteSignature);
RSACryptoServiceProvider key = new RSACryptoServiceProvider();
key.FromXmlString(p_strKeyPrivate);
RSAPKCS1SignatureFormatter formatter = new RSAPKCS1SignatureFormatter(key);
formatter.SetHashAlgorithm("MD5");
byte[] inArray = formatter.CreateSignature(rgbHash);
return Convert.ToBase64String(inArray);
}
/// <summary>
/// 签名验证
/// </summary>
/// <param name="p_strKeyPublic">公钥</param>
/// <param name="p_strHashbyteDeformatter">待验证的用户名</param>
/// <param name="p_strDeformatterData">注册码</param>
/// <returns></returns>
public bool SignatureDeformatter(string p_strKeyPublic, string p_strHashbyteDeformatter, string p_strDeformatterData)
{
try
{
byte[] rgbHash = Convert.FromBase64String(p_strHashbyteDeformatter);
RSACryptoServiceProvider key = new RSACryptoServiceProvider();
key.FromXmlString(p_strKeyPublic);
RSAPKCS1SignatureDeformatter deformatter = new RSAPKCS1SignatureDeformatter(key);
deformatter.SetHashAlgorithm("MD5");
byte[] rgbSignature = Convert.FromBase64String(p_strDeformatterData);
if (deformatter.VerifySignature(rgbHash, rgbSignature))
{
return true;
}
return false;
}
catch
{
return false;
}
}
/// <summary>
/// 获取硬盘ID
/// </summary>
/// <returns>硬盘ID</returns>
public string GetHardID()
{
string HDInfo = "";
ManagementClass cimobject1 = new ManagementClass("Win32_DiskDrive");
ManagementObjectCollection moc1 = cimobject1.GetInstances();
foreach (ManagementObject mo in moc1)
{
HDInfo = (string)mo.Properties["Model"].Value;
}
return HDInfo;
}
/// <summary>
/// 读注册表中指定键的值
/// </summary>
/// <param name="key">键名</param>
/// <returns>返回键值</returns>
private string ReadReg(string key)
{
string temp = "";
try
{
RegistryKey myKey = Registry.LocalMachine;
RegistryKey subKey = myKey.OpenSubKey(@"SOFTWARE/JX/Register");
temp = subKey.GetValue(key).ToString();
subKey.Close();
myKey.Close();
return temp;
}
catch (Exception)
{
throw;//可能没有此注册项;
}
}
/// <summary>
/// 创建注册表中指定的键和值
/// </summary>
/// <param name="key">键名</param>
/// <param name="value">键值</param>
private void WriteReg(string key, string value)
{
try
{
RegistryKey rootKey = Registry.LocalMachine.CreateSubKey(@"SOFTWARE/JX/Register");
rootKey.SetValue(key, value);
rootKey.Close();
}
catch (Exception)
{
throw;
}
}
/// <summary>
/// 创建公钥文件
/// </summary>
/// <param name="path"></param>
/// <param name="publickey"></param>
public void CreatePublicKeyXML(string path, string publickey)
{
try
{
FileStream publickeyxml = new FileStream(path, FileMode.Create);
StreamWriter sw = new StreamWriter(publickeyxml);
sw.WriteLine(publickey);
sw.Close();
publickeyxml.Close();
}
catch
{
throw;
}
}
/// <summary>
/// 创建私钥文件
/// </summary>
/// <param name="path"></param>
/// <param name="privatekey"></param>
public void CreatePrivateKeyXML(string path, string privatekey)
{
try
{
FileStream privatekeyxml = new FileStream(path, FileMode.Create);
StreamWriter sw = new StreamWriter(privatekeyxml);
sw.WriteLine(privatekey);
sw.Close();
privatekeyxml.Close();
}
catch
{
throw;
}
}
/// <summary>
/// 读取公钥
/// </summary>
/// <param name="path"></param>
/// <returns></returns>
public string ReadPublicKey(string path)
{
StreamReader reader = new StreamReader(path);
string publickey = reader.ReadToEnd();
reader.Close();
return publickey;
}
/// <summary>
/// 读取私钥
/// </summary>
/// <param name="path"></param>
/// <returns></returns>
public string ReadPrivateKey(string path)
{
StreamReader reader = new StreamReader(path);
string privatekey = reader.ReadToEnd();
reader.Close();
return privatekey;
}
/// <summary>
/// 初始化注册表，程序运行时调用，在调用之前更新公钥xml
/// </summary>
/// <param name="path">公钥路径</param>
public void InitialReg(string path)
{
Registry.LocalMachine.CreateSubKey(@"SOFTWARE/JX/Register");
Random ra = new Random();
string publickey = this.ReadPublicKey(path);
if (Registry.LocalMachine.OpenSubKey(@"SOFTWARE/JX/Register").ValueCount <= 0)
{
this.WriteReg("RegisterRandom", ra.Next(1,100000).ToString());
this.WriteReg("RegisterPublicKey", publickey);
}
else
{
this.WriteReg("RegisterPublicKey", publickey);
}
}
如果是要对发送的消息进行加密和解密，加密时用公钥，解密时用私钥，即使密文被窃取也无法破解。
如果是要对软件进行注册，生成注册码，则服务端将用户的硬盘号用私钥加密，客户端用公钥解密，解密后将客户端的硬盘号进行MD5加密，将得到的结果和解密后的结果进行比较，如果相同，说明是注册用户，否则为非注册用户。