EdjBX6f3

1import java.net.*;
2import java.io.*;
3import javax.crypto.*;
4import javax.crypto.spec.IvParameterSpec;
5import javax.crypto.spec.SecretKeySpec;
6import java.security.InvalidAlgorithmParameterException;
7import java.security.InvalidKeyException;
8import java.security.MessageDigest;
9import java.security.NoSuchAlgorithmException;
10import java.util.Arrays;
11
12public class Server{
13    public static void main(String args[]){
14        int number=0;
15        try{
16            int serverPort = 4567;
17            ServerSocket listenSocket = new ServerSocket(serverPort);
18            while(true) {
19                Socket clientSocket = listenSocket.accept();
20                new Connection(clientSocket,number);
21                number++;
22            }
23        } catch(IOException e) {
24            System.out.println("Listen:" + e.getMessage());
25        }
26    }
27}
28
29class Connection extends Thread {
30    DataInputStream in;
31    DataOutputStream out;
32    Socket clientSocket;
33    int number;
34    int stopped;
35
36    public Connection (Socket aClientSocket,int clientNumber) {
37        try{
38            number=clientNumber;
39            clientSocket = aClientSocket;
40            in = new DataInputStream(clientSocket.getInputStream());
41            out = new DataOutputStream(clientSocket.getOutputStream());
42            stopped=0;
43            this.start();
44        }catch(IOException e){System.out.println("Connection:" + e.getMessage());}
45    }
46
47    public void run(){
48        try{
49            while(true){
50                //key
51                byte [] key = {1,2,3,4,1,2,3,4,1,2,3,4,1,2,3,4};
52
53                //hash function and new keys
54                MessageDigest md = MessageDigest.getInstance("SHA-256");
55
56                byte [] byte1 = {1};
57                byte [] aux1 = concat(key, byte1);
58                byte [] hash1= md.digest(aux1);
59                SecretKey k1 = new SecretKeySpec(hash1, 0, hash1.length, "AES");
60
61                byte [] byte2 = {2};
62                byte [] aux2 = concat(key, byte2);
63                byte [] hash2= md.digest(aux2);
64                SecretKey k2 = new SecretKeySpec(hash2, 0, hash2.length, "AES");
65
66                //message authentication code
67                Mac mac = Mac.getInstance("HmacSHA256");
68                mac.init(k2);
69                int nSeq = 0;
70
71                //nonce - receives IV in plaintext
72                byte[] nonce=new byte[16];
73                in.read(nonce);
74                IvParameterSpec iv = new IvParameterSpec(nonce);
75
76                //D(m, k1) = c - c is only decrypted if the macs match
77                Cipher c = Cipher.getInstance("AES/CTR/PKCS5Padding");
78                c.init(Cipher.DECRYPT_MODE, k1, iv);
79                int text;
80
81                while (stopped!=1){
82                    try{
83                        //size of the ciphertext
84                        byte sizeInBytes[] = new byte[4];
85
86                        if(in.read(sizeInBytes)!=-1){
87                            int size=convertByteToInt(sizeInBytes);
88
89                            //256 bits represent the mac
90                            byte authTagClient[] = new byte[32];
91                            in.read(authTagClient);
92
93                            //ciphertext
94                            byte ciphertext[] = new byte[size];
95                            in.read(ciphertext);
96
97                            //calculates the server authentication tag
98                            byte [] nSeqByte = intToByteArray(nSeq);
99                            byte [] authTagAux = concat(ciphertext, nSeqByte);
100                            byte [] authTag = mac.doFinal(authTagAux);
101
102                            if(Arrays.equals(authTagClient, authTag)){
103                                byte [] dec=c.doFinal(ciphertext);
104                                System.out.println("Text from client : "+new String (dec));
105                            }
106                            else{
107                                System.out.println("Invalid MAC");
108                            }
109                            nSeq++;
110                        }else{
111                            stopped=1;
112                        }
113                    }
114                    catch (IOException e) {
115                    }
116                }
117
118            }
119        }
120        catch (NoSuchPaddingException e) {
121            e.printStackTrace();
122        }
123
124        catch (NoSuchAlgorithmException e) {
125            e.printStackTrace();
126        }
127        catch (InvalidKeyException e) {
128            e.printStackTrace();
129        }
130        catch (InvalidAlgorithmParameterException e) {
131            e.printStackTrace();
132        } catch (BadPaddingException e) {
133            e.printStackTrace();
134        } catch (IllegalBlockSizeException e) {
135            e.printStackTrace();
136        } catch (IOException e) {
137            e.printStackTrace();
138        }
139    }
140
141    private byte [] concat(byte[] first, byte[] second) throws IOException {
142        ByteArrayOutputStream baos = new ByteArrayOutputStream();
143        baos.write(first);
144        baos.write(second);
145        byte [] result = baos.toByteArray();
146        baos.reset();
147        return result;
148    }
149
150    //https://stackoverflow.com/questions/2183240/java-integer-to-byte-array
151    public static final byte[] intToByteArray(int value) {
152        return new byte[]{
153                (byte)(value >>> 24),
154                (byte)(value >>> 16),
155                (byte)(value >>> 8),
156                (byte)value};
157    }
158
159    //https://stackoverflow.com/questions/4950598/convert-byte-to-int
160    public int convertByteToInt(byte[] b)
161    {
162        int value= 0;
163        for(int i=0; i<b.length; i++)
164            value = (value << 8) | b[i];
165        return value;
166    }
167}