how to store the previous of a variable

[Randa]

Hi ,

I had a problem with XOR before , and it was resolved thx to Norm
i cannot post a thread from there , so... thx

now... how can i store a previous value of a variable

...
smessage=new byte[messagesize];
System.arraycopy(entete2,0,smessage,0,entete2.leng th);
System.arraycopy(HE1,0,smessage,entete2.length,HE1 .length);
System.arraycopy(HE2,0,smessage,(entete2.length+HE 1.length),HE2.length);
System.arraycopy(cipherRnd,0,smessage,(entete2.len gth+HE1.length+HE2.length),cipherRnd.length);

//if the previous packet exists , do xor , else it's the first
if (PrevPkt.getpktclient() != null)
{
//define returned var.
byte[] a = PrevPkt.getpktclient() ;
int len = (smessage.length > a.length) ? smessage.length : a.length ;
byte[] xorResult = new byte[len];
XorB myXor = new XorB();
xorResult = myXor.xorArray(smessage, a , PrevPkt.getpktclient().length );
}
////save packet for future use
PrevPkt p1 = new PrevPkt(smessage , 1) ;

i need to save smessage, so i can use it the next time this method is called
here , i tried storing it in a static variable , it doesn't work

help .

thx

[masijade]

An instance variable?

[Norm]

i need to save smessage, so i can use it the next time this method is called here , i tried storing it in a static variable , it doesn't work

What does "didn't work" mean?
How/where do you save the old value?

PrevPkt p1 = new PrevPkt(smessage , 1) ;
This creates a local variable that will disappear when the method exits.

[Randa]

Hi ,

PrevPkt is a class with setters and getters to hold/retreive the previous value .
the problem is when the method is called , the value of smessage changes
and also the value in PrevPkt , before it's even called
i was using static declarations in the following code then i chaged it :

public class PrevPkt
{
private byte[] pkt ;
private byte[] seq ;

public void setpkt(byte [] mess)
{
this.pkt = mess;
}

public byte[] getpkt()
{
return pkt ;
}

public void setseq(byte[] seq)
{
this.seq = seq;
}

public byte[] getseq()
{
return seq ;
}


is there a way to save the previous value of smessage , in order to reuse it
when the method is called ?

[Norm]

I don't see smessage in the code you just posted. What/where are you talking about?
"when the method is called" - which method is "the method"?

[Randa]

this is the method am working on , i've added remarks to point to my problem

import java.io.*;
import java.security.*;
import java.security.cert.*;
import java.util.*;
import java.util.zip.*;
import javax.crypto.*;
import java.math.*;
import java.lang.*;
import java.lang.reflect.*;

public class SendU_req
{
public byte[] buildMessage(String cername,String key ,byte[] rnd,byte[] SID,byte[] sequenceNumber) throws Exception
{
byte firstByte = 82;
Date start=new Date();
Long l=start.getTime();
Short sh =l.shortValue();
byte timestamplow=sh.byteValue();
l=l.rotateRight(l,8);
sh=l.shortValue();
byte timestamphigh=sh.byteValue();
byte exthigh=0;
byte extlow1=8;
FileInputStream fis=new FileInputStream(cername);
CertificateFactory cf=CertificateFactory.getInstance("X.509");
Collection c=cf.generateCertificates(fis);
Iterator i=c.iterator();
java.security.cert.Certificate cert = (java.security.cert.Certificate)i.next();
byte[] certstream=cert.getEncoded();
//System.out.println("cert"+certstream.length);
int HEdatalength=certstream.length;
HEdatalength=HEdatalength+4;
Integer HEdatalen=HEdatalength;
byte HEdatalow=HEdatalen.byteValue();
HEdatalen=HEdatalen.rotateRight(HEdatalen,8);
byte HEdatahigh=HEdatalen.byteValue();
byte extlow2=16;
byte[] usercap="AES;HMACwithSHA1;DiffieHellman".getBytes( );
//System.out.println("usercap"+usercap.length);
int HEdatalength2=usercap.length;
HEdatalength2=HEdatalength2+4;
Integer HEdatalen2=HEdatalength2;
byte HEdatalow2=HEdatalen2.byteValue();
HEdatalen2=HEdatalen2.rotateRight(HEdatalen2,8);
byte HEdatahigh2=HEdatalen2.byteValue();

KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
char[] password ={'p','a','s','s','w','o','r','d'};
java.io.FileInputStream fis1 =
new java.io.FileInputStream(".keystore");
ks.load(fis1, password);
fis.close();
fis1.close();
// get my private key
char[] keypassword ={'1','2','3','4','5','6'};
PrivateKey myPrivateKey = (PrivateKey)ks.getKey(key, keypassword);
Cipher rsaCipher = Cipher.getInstance("RSA");
// Initialize the cipher for encryption
rsaCipher.init(Cipher.ENCRYPT_MODE, myPrivateKey);
byte[] cipherRnd = rsaCipher.doFinal(rnd);
//System.out.println(cipherRnd.length);


Integer messagesize=12+HEdatalength+HEdatalength2+cipherRn d.length;
byte messagelenlow=messagesize.byteValue();
messagesize=messagesize.rotateRight(messagesize,8) ;
byte messagelenhigh=messagesize.byteValue();
byte[] entete=new byte[8];
entete[0]=firstByte;
entete[1]=SID[0];
entete[2]=messagelenhigh;
entete[3]=messagelenlow;
entete[4]=sequenceNumber[0];
entete[5]=sequenceNumber[1];
entete[6]=timestamphigh;
entete[7]=timestamplow;

byte[] HE1=new byte[HEdatalength];
HE1[0]=exthigh;
HE1[1]=extlow1;
HE1[2]=HEdatahigh;
HE1[3]=HEdatalow;
System.arraycopy(certstream,0,HE1,4,certstream.len gth);

byte[] HE2=new byte[HEdatalength2];
HE2[0]=exthigh;
HE2[1]=extlow2;
HE2[2]=HEdatahigh2;
HE2[3]=HEdatalow2;
System.arraycopy(usercap,0,HE2,4,usercap.length);
messagesize=8+HEdatalength+HEdatalength2+cipherRnd .length;

byte[] smessage=new byte[messagesize];
System.arraycopy(entete,0,smessage,0,entete.length );
System.arraycopy(HE1,0,smessage,entete.length,HE1. length);
System.arraycopy(HE2,0,smessage,(entete.length+HE1 .length),HE2.length);
System.arraycopy(cipherRnd,0,smessage,(entete.leng th+HE1.length+HE2.length),cipherRnd.length);

CheckedInputStream cis=new CheckedInputStream(new ByteArrayInputStream(smessage),new CRC32());
byte[] buf=new byte[32];
while(cis.read(buf)>0){}
Long checksum=cis.getChecksum().getValue();
byte bb1=checksum.byteValue();
checksum=checksum.rotateRight(checksum,8);
byte bb2=checksum.byteValue();
checksum=checksum.rotateRight(checksum,8);
byte bb3=checksum.byteValue();
checksum=checksum.rotateRight(checksum,8);
byte bb4=checksum.byteValue();
byte[] bb={bb1,bb2,bb3,bb4};

byte[] entete2=new byte[12];
System.arraycopy(entete,0,entete2,0,entete.length) ;
System.arraycopy(bb,0,entete2,8,4);

messagesize=12+HEdatalength+HEdatalength2+cipherRn d.length;

smessage=new byte[messagesize];
System.arraycopy(entete2,0,smessage,0,entete2.leng th);
System.arraycopy(HE1,0,smessage,entete2.length,HE1 .length);
System.arraycopy(HE2,0,smessage,(entete2.length+HE 1.length),HE2.length);
System.arraycopy(cipherRnd,0,smessage,(entete2.len gth+HE1.length+HE2.length),cipherRnd.length);

//i have to check if it's the first smessage then i will not do the XOR
System.out.println("at end previou paket =="+ PrevPkt.getpktclient() );
//if the previous packet exists , do xor , else it's the first
if (PrevPkt.getpktclient() != null)
{
//define returned var.
byte[] a = PrevPkt.getpktclient() ;
int len = (smessage.length > a.length) ? smessage.length : a.length ;
byte[] xorResult = new byte[len];
//call XOR method to compute the FEC
XorB myXor = new XorB();
xorResult = myXor.xorArray(smessage, a , PrevPkt.getpktclient().length );
//add the result fec to smessage
messagesize =smessage.length + xorResult.length;
byte[] newsvsp =new byte[messagesize];
System.arraycopy(smessage,0,newsvsp,0,smessage.len gth);
System.arraycopy(xorResult,0,newsvsp,smessage.leng th,xorResult.length);
}

//i have to save acopy of smessage, so the next time this method is called i can do the XOR
// PrevPkt p1 = new PrevPkt(smessage , 1) ;

//Signature should be done on newsvsp
//
//Signature added on all packet
Signature rsa=Signature.getInstance("MD5withRSA");
rsa.initSign(myPrivateKey);
rsa.update(smessage);
byte[] sig=rsa.sign();
// System.out.println("signature"+sig.length);
byte[] message=new byte[(sig.length+messagesize)];
System.arraycopy(smessage,0,message,0,messagesize) ;
System.arraycopy(sig,0,message,messagesize,sig.len gth);
return (message);

}
}


with PrevPkt class , i was trying to store a copy of smessage
i did not work

is there a way in java , to hold the value of a variable , untill you want to change it ?

[Randa]

Am only moddifying the code
i did not write it !!:)

[Norm]

Without formatting I can NOT follow the logic of your code. It is too hard to read. I can't see where methods begin or end.
Please use code tags around your code to preserver formatting.
Also add boundary line comments at the beginning of methods:
//*******************************************

hold the value of a variable , untill you want to change it

Where do you have to save the data? Can it be saved in a class variable? As long as the instance of the class exists, the values of its variables will exist.

A class variable:
String saveSMsg; // we'll save smessage here
....
in a method:
saveSMsg = smessage; // save smessage