this is exception
Exception in thread "main" java.security.NoSuchAlgorithmException: RSA Signature not available
at java.security.Signature.getInstance(Signature.java:229)
at MailClient.main(MailClient.java:52)
this is my code
import java.io.*;
import java.net.*;
import java.nio.ByteBuffer;
import java.util.*;
import java.security.*;
public class MailClient {
public String getMessage(Mail m){
return m.message;
}
public static void main(String[] args) throws Exception {
// Initialisation
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String host = args[0];
int port = Integer.parseInt(args[1]);
String userid = args[2];
while(true) {
// connect to server
Socket s = new Socket(host,port);
DataInputStream dis = new DataInputStream(s.getInputStream());
DataOutputStream dos = new DataOutputStream(s.getOutputStream());
ObjectOutputStream oos = new ObjectOutputStream(s.getOutputStream());
oos.flush();
ObjectInputStream ois = new ObjectInputStream(s.getInputStream());
// TO DO: login
// these two lines are here just to make the supplied programs run without crashing.
// You may want to change them, and certainly add things after them
dos.writeUTF(userid);
String userPrivateKeyFileName = userid + ".prv";
// Get the key to create the signature
ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(userPrivateKeyFileName));
PrivateKey privateKey = (PrivateKey)keyIn.readObject();
keyIn.close();
// create timeStamp and random number
long t1 = (new Date()).getTime();
double q1 = Math.random();
// ByteBuffer to convert to bytes later
ByteBuffer bb = ByteBuffer.allocate(16);
bb.putLong(t1);
bb.putDouble(q1);
// create signature, using timeStamp and random number as data
Signature sig = Signature.getInstance("RSA");
sig.initSign(privateKey);
sig.update(bb.array());
byte[] signature = sig.sign();
// send data and signature
DataOutputStream out = new DataOutputStream(s.getOutputStream());
out.writeUTF(userid);
out.writeLong(t1);
out.writeDouble(q1);
out.writeInt(signature.length);
out.write(signature);
out.flush();
boolean answer = dis.readBoolean();
//passed the verifyLogin
if (answer)
{
// receive how many messages
int numMsg = dis.readInt();
System.out.println("You have " + numMsg + " incoming messages.");
// TO DO: read messages
ArrayList<Mail> msg = new ArrayList<>(numMsg);
for(int i=0;i<numMsg;i++){
//@Unchecked
msg = (ArrayList<Mail>) ois.readObject();
}
while(!msg.isEmpty()){
//for each mail, display sender,timestamp,message
System.out.println(msg.get(0).sender);
System.out.println(msg.get(0).timestamp);
System.out.println(msg.get(0).message);
MessageDigest md = MessageDigest.getInstance("SHA-1");
md.update(msg.get(0).hashcash);
byte[] digest = md.digest();
boolean normalMail = msg.get(0).checkHashcash(digest);
if(normalMail){
//check each mail is original that it isn't modified
//receive mail
System.out.println(msg.get(0).message);
}
else{System.out.println("it's a spam message.");
System.out.println(msg.get(0).message);
}
msg.remove(0);
}
// send messages
System.out.println("Do you want to send a message [Y/N]?");
String wantToSend = br.readLine();
if (!wantToSend.equals("Y")) {
dos.writeBoolean(false);
return ;
}
dos.writeBoolean(true);
System.out.println("Enter userid of recipient:");
String recipient = br.readLine();
System.out.println("Type your message:");
String message = br.readLine();
// TO DO: send mail
Mail m = new Mail(userid, recipient, message);
MessageDigest md = MessageDigest.getInstance("SHA-1");
md.update(m.hashcash);
byte[] digest = md.digest();
while(m.checkHashcash(digest)){
m.setHashcash(digest);
}
out.write(digest);
out.flush();
// send timeStamp and digest to server
long mailTimestamp = m.timestamp.getTime();
out.writeLong(mailTimestamp);
oos.writeObject(m);
}
}
}
}
