网络数据加密需要解决三个问题:
完整:数据不被篡改; 安全:数据不被截获,或者截获也无法得到明文; 可靠:数据从真正的发送方而来,其他人无法伪造一个数据来欺骗接受方; 下面例子只解决了安全这个问题: 非对称算法使用的两个密钥有如下关系:使用公共密钥加密的信息只能被相应的私有密钥解密。因此,我首要求你给我发送你的公共密钥。在发送给我的途中可能有人会截取它,但是没有关系,因为他们只能使用该密钥给你的信息加密。我使用你的公共密钥加密文档并发送给你。你使用私有密钥解密该文档,这是唯一可以解密的密钥,并且没有通过网络传递。 不对称算法比对称算法计算的花费多、速度慢。因此我们不希望在线对话中使用不对称算法加密所有信息。相反,我们使用对称算法。下面的例子中我们使用不对称加密来加密对称密钥。接着就使用对称算法加密了。实际上安全接口层(SSL)建立服务器和浏览器之间的安全对话使用的就是这种工作方式。 示例是一个TCP程序,分为服务器端和客户端。服务器端的工作流程是: 从客户端接收公共密钥。 使用公共密钥加密未来使用的对称密钥。 将加密了的对称密钥发送给客户端。 给客户端发送使用该对称密钥加密的信息。 代码如下:
namespace com.billdawson.crypto
{ public class CryptoServer { private const int RSA_KEY_SIZE_BITS = 1024; private const int RSA_KEY_SIZE_BYTES = 252; private const int TDES_KEY_SIZE_BITS = 192; public static void Main(string[] args) { int port; string msg; TcpListener listener; TcpClient client; SymmetricAlgorithm symm; RSACryptoServiceProvider rsa; //获取端口 try { port = Int32.Parse(args[0]); msg = args[1]; } catch { Console.WriteLine(USAGE); return; } //建立监听 try { listener = new TcpListener(port); listener.Start(); Console.WriteLine("Listening on port {0}",port); client = listener.AcceptTcpClient(); Console.WriteLine("connection."); } catch (Exception e) { Console.WriteLine(e.Message); Console.WriteLine(e.StackTrace); return; } try { rsa = new RSACryptoServiceProvider(); rsa.KeySize = RSA_KEY_SIZE_BITS; // 获取客户端公共密钥 rsa.ImportParameters(getClientPublicKey(client)); symm = new TripleDESCryptoServiceProvider(); symm.KeySize = TDES_KEY_SIZE_BITS; //使用客户端的公共密钥加密对称密钥并发送给客。 encryptAndSendSymmetricKey(client, rsa, symm); //使用对称密钥加密信息并发送 encryptAndSendSecretMessage(client, symm, msg); } catch (Exception e) { Console.WriteLine(e.Message); Console.WriteLine(e.StackTrace); } finally { try { client.Close(); listener.Stop(); } catch { //错误 } Console.WriteLine("Server exiting"); } } private static RSAParameters getClientPublicKey(TcpClient client) { // 从字节流获取串行化的公共密钥,通过串并转换写入类的实例 byte[] buffer = new byte[RSA_KEY_SIZE_BYTES]; NetworkStream ns = client.GetStream(); MemoryStream ms = new MemoryStream(); BinaryFormatter bf = new BinaryFormatter(); RSAParameters result; int len = 0; int totalLen = 0; while(totalLen (len = ns.Read(buffer,0,buffer.Length))>0) { totalLen+=len; ms.Write(buffer, 0, len); } ms.Position=0; result = (RSAParameters)bf.Deserialize(ms); ms.Close(); return result; } private static void encryptAndSendSymmetricKey( TcpClient client, RSACryptoServiceProvider rsa, SymmetricAlgorithm symm) { // 使用客户端的公共密钥加密对称密钥 byte[] symKeyEncrypted; byte[] symIVEncrypted; NetworkStream ns = client.GetStream(); symKeyEncrypted = rsa.Encrypt(symm.Key, false); symIVEncrypted = rsa.Encrypt(symm.IV, false); ns.Write(symKeyEncrypted, 0, symKeyEncrypted.Length); ns.Write(symIVEncrypted, 0, symIVEncrypted.Length); } private static void encryptAndSendSecretMessage(TcpClient client, SymmetricAlgorithm symm, string secretMsg) { // 使用对称密钥和初始化矢量加密信息并发送给客户端 byte[] msgAsBytes; NetworkStream ns = client.GetStream(); ICryptoTransform transform = symm.CreateEncryptor(symm.Key,symm.IV); CryptoStream cstream = new CryptoStream(ns, transform, CryptoStreamMode.Write); msgAsBytes = Encoding.ASCII.GetBytes(secretMsg); cstream.Write(msgAsBytes, 0, msgAsBytes.Length); cstream.FlushFinalBlock(); } } 客户端的工作流程是: 建立和发送公共密钥给服务器。 从服务器接收被加密的对称密钥。 解密该对称密钥并将它作为私有的不对称密钥。 接收并使用不对称密钥解密信息。 代码如下:
namespace com.billdawson.crypto
{ public class CryptoClient { private const int RSA_KEY_SIZE_BITS = 1024; private const int RSA_KEY_SIZE_BYTES = 252; private const int TDES_KEY_SIZE_BITS = 192; private const int TDES_KEY_SIZE_BYTES = 128; private const int TDES_IV_SIZE_BYTES = 128; public static void Main(string[] args) { int port; string host; TcpClient client; SymmetricAlgorithm symm; RSACryptoServiceProvider rsa; if (args.Length!=2) { Console.WriteLine(USAGE); return; } try { host = args[0]; port = Int32.Parse(args[1]); } catch { Console.WriteLine(USAGE); return; } try //连接 { client = new TcpClient(); client.Connect(host,port); } catch(Exception e) { Console.WriteLine(e.Message); Console.Write(e.StackTrace); return; } try { Console.WriteLine("Connected. Sending public key."); rsa = new RSACryptoServiceProvider(); rsa.KeySize = RSA_KEY_SIZE_BITS; sendPublicKey(rsa.ExportParameters(false),client); symm = new TripleDESCryptoServiceProvider(); symm.KeySize = TDES_KEY_SIZE_BITS; MemoryStream ms = getRestOfMessage(client); extractSymmetricKeyInfo(rsa, symm, ms); showSecretMessage(symm, ms); } catch(Exception e) { Console.WriteLine(e.Message); Console.Write(e.StackTrace); } finally { try { client.Close(); } catch { //错误 } } } private static void sendPublicKey( RSAParameters key, TcpClient client) { NetworkStream ns = client.GetStream(); BinaryFormatter bf = new BinaryFormatter(); bf.Serialize(ns,key); } private static MemoryStream getRestOfMessage(TcpClient client) { //获取加密的对称密钥、初始化矢量、秘密信息。对称密钥用公共RSA密钥 //加密,秘密信息用对称密钥加密 MemoryStream ms = new MemoryStream(); NetworkStream ns = client.GetStream(); byte[] buffer = new byte[1024]; int len=0; // 将NetStream 的数据写入内存流 while((len = ns.Read(buffer, 0, buffer.Length))>0) { ms.Write(buffer, 0, len); } ms.Position = 0; return ms; } private static void extractSymmetricKeyInfo( RSACryptoServiceProvider rsa, SymmetricAlgorithm symm, MemoryStream msOrig) { MemoryStream ms = new MemoryStream(); // 获取TDES密钥--它被公共RSA密钥加密,使用私有密钥解密 byte[] buffer = new byte[TDES_KEY_SIZE_BYTES]; msOrig.Read(buffer,0,buffer.Length); symm.Key = rsa.Decrypt(buffer,false); // 获取TDES初始化矢量 buffer = new byte[TDES_IV_SIZE_BYTES]; msOrig.Read(buffer, 0, buffer.Length); symm.IV = rsa.Decrypt(buffer,false); } private static void showSecretMessage( SymmetricAlgorithm symm, MemoryStream msOrig) { //内存流中的所有数据都被加密了 byte[] buffer = new byte[1024]; int len = msOrig.Read(buffer,0,buffer.Length); MemoryStream ms = new MemoryStream(); ICryptoTransform transform = symm.CreateDecryptor(symm.Key,symm.IV); CryptoStream cstream =new CryptoStream(ms, transform, CryptoStreamMode.Write); cstream.Write(buffer, 0, len); cstream.FlushFinalBlock(); // 内存流现在是解密信息,是字节的形式,将它转换为字符串 ms.Position = 0; len = ms.Read(buffer,0,(int) ms.Length); ms.Close(); string msg = Encoding.ASCII.GetString(buffer,0,len); Console.WriteLine("The host sent me this secret message:"); Console.WriteLine(msg); } } }
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