/******* Class KarnPrintWriter **********
  Copyright (c) 2004 Coleman Kane

  Written for: John V. Franco
               University of Cincinnati
               Computer Science
               20-ECES-694 Advanced Topics in Computer Science
**/
import java.io.*;
import java.lang.*;
import java.math.*;
import java.security.*;

public class KarnBufferedReader extends BufferedReader {
	/*********************
	  * The Karn Symmetric Encryption portion of the Monitor
	  * client
	  ********************/
	private BigInteger sharedSecret;
	private MessageDigest md;

	public KarnBufferedReader(Reader in, BigInteger sKey) {
		super(in);
		sharedSecret = sKey;
		try {
			md = MessageDigest.getInstance("SHA");
		} catch(Exception x) {
			System.out.println("Can't make SHA digests");
			md = null;
		}
	}

	public String decrypt(String msg) {
		String result = "";
        if(msg == null)
            return "";
		BigInteger msgNum = new BigInteger(msg, 32);
		byte m[] = msgNum.toByteArray();
		md.reset();
		int mOffset = 0;

		if(m[0] == 0x2a)
			for(;m.length > 1 + mOffset;) {
                byte key[] = sharedSecret.toByteArray();
				byte mLeft[] = new byte[20];
				byte mRight[] = new byte[20];
				byte kLeft[] = new byte[key.length/2];
				byte kRight[] = new byte[key.length/2];
				byte tmp[] = new byte[20];


				for(int i = 0; i < 20; i++) {
					mRight[i] = m[i + 21 + mOffset];
					mLeft[i] = m[i + 1 + mOffset];
				}

                for(int i = 0; i < key.length/2; i++) {
                    kRight[i] = key[i + key.length/2];
                    kLeft[i] = key[i];
                }

				md.update(mRight);
				md.update(kRight);
				tmp = md.digest();
				for(int i = 0; i < tmp.length; i++)
					tmp[i] ^= mLeft[i];
				try {
					result += new String(tmp, "ISO-8859-1");
				} catch(UnsupportedEncodingException uex) {
					System.out.println("Bad encoding, you are screwed");
					return null;
				}

				md.reset();
				md.update(tmp);
				md.update(kLeft);
				tmp = md.digest();
				for(int i = 0; i < tmp.length; i++)
					tmp[i] ^= mRight[i];
				try {
					result += new String(tmp, "ISO-8859-1");
				} catch(UnsupportedEncodingException uex) {
					System.out.println("Bad encoding, you are screwed");
					return null;
				}
				md.reset();
				mOffset += 40;
			}
		return result;
	}

	public String readLine() throws IOException {
		String line = decrypt(super.readLine());
		if(line.indexOf(0) > -1)
			line = line.substring(0, line.indexOf(0));
		return line;
	}
}