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);
}
}
}