前面两部分分别讲解了如何在.net程序中使用SSL实现安全通信以及SSL的通信过程,并通过抓包工具具体分析了ssl的握手过程,本文通过一个demo来模拟ssl协议,在TCP之上实现自己的安全通信。
创建证书
为了实现安全的通信,必须使用证书对传输的数据进行加密,有两种方法可以得到证书,一是安装CA服务器,使用CA来发放证书,二是通过makecert.exe工具自己创建。
创建服务器证书:
cmd>makecert.exe -r -pe -n "CN=MySslServer" -sky Exchange -ss My
创建客户端证书
cmd>makecert.exe -r -pe -n "CN=MySslClient" -sky Exchange -ss My
关于makecert.exe的更多信息可以操作这里。
建立TCP连接
使用普通的Socket类来建立TCP连接即可。后续的握手,传输数据都是在TCP之上的,在这里,定义每条信息的第一个字节是类型,0x01是整数,0x02是session key,0x03是应用层数据,0x04是错误信息,未使用。
我们知道TCP通信是stream的,消息没有边界,有可能发送方发送的数据,在接收方两次才能接收完,或者发送方连续发送两次数据,接收方一次就全部接受,这就要求应用层自己对消息的边界进行区分,常用的有3种方法,一是固定长度,所有消息长度一样,不够就填充,显然不够实用而且浪费带宽;二是定义消息边界,每条消息以固定字节流结尾如
交换证书
在TCP连接建立之后,开始进行握手过程,主要是交换证书,交换session key。
server与client各自将自己的证书发送给对方,证书被export成.cer格式,只含有public key。证书的作用一是交换session key,二是发送数据时签名。
2 byte [] sentBytes = AddType(certBytes, type);
3 so.workSocket.Send(sentBytes, 0 , sentBytes.Length, SocketFlags.None);
4 Console.WriteLine( " Send>>>>>>>>>>>>>>>>>>>>> " );
5 PrintCert(so.localCert);
6 。。。。。。
7 byte [] data = RemoveType(so.buffer, read);
8 so.remoteCert = new X509Certificate2(data);
9 Console.WriteLine( " Recv<<<<<<<<<<<<<<<<<<<<<< " );
10 PrintCert(so.remoteCert);
交换session key
本demo使用DES对称算法来加密,必须在发送应用层数据之前交换算法的key,使用双方约定固定的IV。
其中一方生成随机的key,用对方的证书加密,调用RSA的Encrypt方法,会使用Public key,将加密后的数据发送给对方,由于只有对方才有证书的private key,所以也只有对方才能解密出key,第三方即使中途截获了数据也不能破解出key。
2 byte [] encrypedSessionKey = rsa.Encrypt(so.localSessionKey, false );
3 byte [] sentBytes = AddType(encrypedSessionKey, type);
4 so.workSocket.Send(sentBytes, 0 , sentBytes.Length, SocketFlags.None);
5 Console.WriteLine( " Send>>>>>>>>>>>>>>>>>>>>> " );
6 PrintSessionKey(so.localSessionKey);
2 RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)so.localCert.PrivateKey;
3 so.remoteSessionKey = rsa.Decrypt(data, false );
4 Console.WriteLine( " Recv<<<<<<<<<<<<<<<<<<<<<< " );
5 PrintSessionKey(so.remoteSessionKey);
发送加密和签名数据
发送数据使用DES算法加密,防止被第三方截获;同时对发送的数据签名,让对方确认数据没有被篡改并且确认数据是自己发送的。
数据格式:
0x03 |
密文长度 |
密文 |
签名长度 |
签名 |
2
3 // encrypt
4 DESCryptoServiceProvider des = new DESCryptoServiceProvider();
5 ICryptoTransform cTransform = des.CreateEncryptor(so.remoteSessionKey, new byte [ 8 ]);
6 MemoryStream ms = new MemoryStream();
7 CryptoStream encStream = new CryptoStream(ms, cTransform, CryptoStreamMode.Write);
8 encStream.Write(so.sentData, 0 , so.sentData.Length);
9 encStream.FlushFinalBlock();
10
11 byte [] temp = ms.ToArray();
12 memoryStream.Write(BitConverter.GetBytes(temp.Length), 0 , 4 );
13 memoryStream.Write(temp, 0 , temp.Length);
14
15 // hash
16 MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
17 byte [] hash = md5.ComputeHash(so.sentData);
18
19 // sign
20 RSACryptoServiceProvider rsa = (RSACryptoServiceProvider) so.localCert.PrivateKey;
21 byte [] sign = rsa.SignHash(hash, CryptoConfig.MapNameToOID( " MD5 " ));
22
23 memoryStream.Write(BitConverter.GetBytes(sign.Length), 0 , 4 );
24 memoryStream.Write(sign, 0 , sign.Length);
25
26 byte [] sentBytes = AddType(memoryStream.ToArray(), type);
27 so.workSocket.Send(sentBytes, 0 , sentBytes.Length, SocketFlags.None);
28 Console.WriteLine( " Send>>>>>>>>>>>>>>>>>>>>> " );
29 PrintData(so.sentData);
2
3 // Decrypt
4 DESCryptoServiceProvider des = new DESCryptoServiceProvider();
5 ICryptoTransform cTransform = des.CreateDecryptor(so.localSessionKey, new byte [ 8 ]);
6 int len = BitConverter.ToInt32(data, 0 );
7 byte [] cipherText = new byte [len];
8 Array.Copy(data, 4 , cipherText, 0 , len);
9 MemoryStream ms2 = new MemoryStream(cipherText);
10 CryptoStream decStream = new CryptoStream(ms2, cTransform, CryptoStreamMode.Read);
11
12 Byte[] tempBuffer = new Byte[ 1024 ];
13 Byte[] outputBytes = new byte [ 0 ];
14 int nRead = decStream.Read(tempBuffer, 0 , tempBuffer.Length);
15 int nLength = 0 ;
16 while ( 0 != nRead)
17 {
18 nLength = outputBytes.Length;
19 Array.Resize( ref outputBytes, nLength + nRead);
20 Array.Copy(tempBuffer, 0 , outputBytes, nLength, nRead);
21 nRead = decStream.Read(tempBuffer, 0 , tempBuffer.Length);
22 }
23 so.recvData = outputBytes;
24 Console.WriteLine( " Recv<<<<<<<<<<<<<<<<<<<<<< " );
25 PrintData(so.recvData);
26
27 // hash
28 MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
29 byte [] hash = md5.ComputeHash(so.recvData);
30
31 // verify
32 int signlen = BitConverter.ToInt32(data, len + 4 );
33 byte [] sign = new byte [signlen];
34 Array.Copy(data, 4 + len + 4 ,sign, 0 , signlen);
35 RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)so.remoteCert.PublicKey.Key;
36 try
37 {
38 bool verify = rsa.VerifyHash(hash, CryptoConfig.MapNameToOID( " MD5 " ), sign);
39 if (verify)
40 {
41 Console.WriteLine( " verify correct! " );
42 }
43 else
44 {
45 Console.WriteLine( " verify error! " );
46 }
47 }
48 catch
49 {
50 Console.WriteLine( " verify error! " );
51 return PackageType.Error;
52 }
2 Recv <<<<<<<<<<<<<<<<<<<<<<
3 ============================================
4 cert
5 ============================================
6 Subject: CN = MySslClient
7 Issuer: CN = MySslClient
8 Version: 3
9 Valid Date: 7 / 7 / 2010 11 : 25 : 28 AM
10 Expiry Date: 1 / 1 / 2040 7 : 59 : 59 AM
11 Thumbprint: D9AE7CF97A254FCA05EB7B704DDC90878FC56B0C
12 Serial Number: 2500552056343D874C0B714A71CB047B
13 Friendly Name: RSA
14 Public Key Format: 30 81 89 02 81 81 00 9f 6f 17 84 0f 03 a0 8c b7 86 45 49 ba 0c c5 ab 37 c9 30 24 32 b5 dc 90 31 e4 d6
15 ea 83 45 1f c8 2d dd 2f 81 3e da 09 44 7f 2a cf bb 18 9a 92 28 d3 79 f0 33 b8 04 f2 1a 1d f8 e0 b6 f9 cc da 36 16 2b e3
16 8b 8d 82 5f 9c 88 6a 79 54 53 4f 08 10 dc b9 53 f1 c8 d4 bd 3d c4 94 71 1d db a2 76 65 8c 37 a3 cd 88 0d a0 72 0e 93 3a
17 64 62 dc 90 cf 19 3f f7 58 59 d6 bd 4e 3f a4 15 30 5b 36 75 2f 02 03 01 00 01
18 Send >>>>>>>>>>>>>>>>>>>>>
19 ============================================
20 cert
21 ============================================
22 Subject: CN = MySslServer
23 Issuer: CN = MySslServer
24 Version: 3
25 Valid Date: 7 / 7 / 2010 11 : 25 : 32 AM
26 Expiry Date: 1 / 1 / 2040 7 : 59 : 59 AM
27 Thumbprint: 5B1CEC828E92A64950284E557477FDD7E2C05300
28 Serial Number: 907E95210C949144FD68342B32FD07
29 Friendly Name: RSA
30 Public Key Format: 30 81 89 02 81 81 00 a4 97 38 0d dd c7 fa 6b b3 e6 23 17 df cd bf 06 c7 40 e1 5e 9a 04 81 02 62 00 b5
31 52 82 c9 6d b0 fc 16 ce e8 72 be ae 31 80 85 44 75 6c 1d 6a 2c 33 55 ee 04 6a fd f8 f4 ff 3a e0 22 28 a7 4f f8 c4 ba 96
32 c7 e6 f0 27 aa 43 09 11 ce eb cb 5e fe 63 84 ef e0 74 11 99 91 5d a0 39 5b 54 e6 74 8d db c8 ce d2 bd 08 53 63 19 3d d6
33 4c 37 99 b1 28 6a 07 2b 0c 70 49 fa df 9e ed 8b 2d e0 ed bf 03 02 03 01 00 01
34 Send >>>>>>>>>>>>>>>>>>>>>
35 ============================================
36 session key
37 ============================================
38 Session Key: 44 97 AC 07 5E 41 27 0B[ 8 ]
39 Recv <<<<<<<<<<<<<<<<<<<<<<
40 ============================================
41 session key
42 ============================================
43 Session Key: BD 28 62 18 04 90 C9 57 [ 8 ]
44 Recv <<<<<<<<<<<<<<<<<<<<<<
45 ============================================
46 data
47 ============================================
48 It ' s just a text.
49 verify correct !
50 Send >>>>>>>>>>>>>>>>>>>>>
51 ============================================
52 data
53 ============================================
54 Response to client.
2 Send >>>>>>>>>>>>>>>>>>>>>
3 ============================================
4 cert
5 ============================================
6 Subject: CN = MySslClient
7 Issuer: CN = MySslClient
8 Version: 3
9 Valid Date: 7 / 7 / 2010 11 : 25 : 28 AM
10 Expiry Date: 1 / 1 / 2040 7 : 59 : 59 AM
11 Thumbprint: D9AE7CF97A254FCA05EB7B704DDC90878FC56B0C
12 Serial Number: 2500552056343D874C0B714A71CB047B
13 Friendly Name: RSA
14 Public Key Format: 30 81 89 02 81 81 00 9f 6f 17 84 0f 03 a0 8c b7 86 45 49 ba 0c c5 ab 37 c9 30 24 32 b5 dc 90 31 e4 d6
15 ea 83 45 1f c8 2d dd 2f 81 3e da 09 44 7f 2a cf bb 18 9a 92 28 d3 79 f0 33 b8 04 f2 1a 1d f8 e0 b6 f9 cc da 36 16 2b e3
16 8b 8d 82 5f 9c 88 6a 79 54 53 4f 08 10 dc b9 53 f1 c8 d4 bd 3d c4 94 71 1d db a2 76 65 8c 37 a3 cd 88 0d a0 72 0e 93 3a
17 64 62 dc 90 cf 19 3f f7 58 59 d6 bd 4e 3f a4 15 30 5b 36 75 2f 02 03 01 00 01
18 Recv <<<<<<<<<<<<<<<<<<<<<<
19 ============================================
20 cert
21 ============================================
22 Subject: CN = MySslServer
23 Issuer: CN = MySslServer
24 Version: 3
25 Valid Date: 7 / 7 / 2010 11 : 25 : 32 AM
26 Expiry Date: 1 / 1 / 2040 7 : 59 : 59 AM
27 Thumbprint: 5B1CEC828E92A64950284E557477FDD7E2C05300
28 Serial Number: 907E95210C949144FD68342B32FD07
29 Friendly Name: RSA
30 Public Key Format: 30 81 89 02 81 81 00 a4 97 38 0d dd c7 fa 6b b3 e6 23 17 df cd bf 06 c7 40 e1 5e 9a 04 81 02 62 00 b5
31 52 82 c9 6d b0 fc 16 ce e8 72 be ae 31 80 85 44 75 6c 1d 6a 2c 33 55 ee 04 6a fd f8 f4 ff 3a e0 22 28 a7 4f f8 c4 ba 96
32 c7 e6 f0 27 aa 43 09 11 ce eb cb 5e fe 63 84 ef e0 74 11 99 91 5d a0 39 5b 54 e6 74 8d db c8 ce d2 bd 08 53 63 19 3d d6
33 4c 37 99 b1 28 6a 07 2b 0c 70 49 fa df 9e ed 8b 2d e0 ed bf 03 02 03 01 00 01
34 Send >>>>>>>>>>>>>>>>>>>>>
35 ============================================
36 session key
37 ============================================
38 Session Key: BD 28 62 18 04 90 C9 57 [ 8 ]
39 Recv <<<<<<<<<<<<<<<<<<<<<<
40 ============================================
41 session key
42 ============================================
43 Session Key: 44 97 AC 07 5E 41 27 0B[ 8 ]
44 Send >>>>>>>>>>>>>>>>>>>>>
45 ============================================
46 data
47 ============================================
48 It ' s just a text.
49 Recv <<<<<<<<<<<<<<<<<<<<<<
50 ============================================
51 data
52 ============================================
53 Response to client.
54 verify correct !
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