urgent ! writing a java card applet -APDU problem
hi
i'm fairly new to the java programming language. i'm trying to write an RSA java card applet to run on a java card simulator.
I am not sure at all what code i need to write for the CLA byte in the command APDU and what code i need to write for the INS byte in the command APDU, and where exactly to put it in my program.
if anybody knows please could you help me out.
So far i have written the code below.
thanx
louise
import javacard.framework.*;
import java.math.*;
import java.util.*;
/*the public key is the public part of the key. Anyone
can have it. It can only encrypt data, not decrypt.*/
public class publickey extends Applet{
//code of the CLA byte in the command APDU header
final static byte publickey_CLA = (byte)0x00;
//max number of characters for text message is 60
final static char MAX_TXT_MSG = 0x3c;
//MAX number of tries (3) before PIN is blocked
final static byte PIN_TRY_LIMIT = (byte)0x03;
//size of PIN must be 4 digits long
final static byte PIN_SIZE = (byte)0x04;
//below status word(SW) values are returned by applet
//in certain circumstances:
//signal that the PIN verification failed
final static short SW_PIN_VERIFICATION_FAIL = 0x6300;
//signal that PIN validation required for txt msging
final static short SW_PIN_VERIFICATION_REQUIRED = 0x630;
//instance variables declaration
OwnerPIN pin; //variable for holding owners pin
BigInteger n,e;
String owner;//variable for holding owners name
/*make a public key. Do not do it yourself, but
make a public key from a private key.*/
publickey(String iowner,BigInteger in,BigInteger ie){
owner=iowner;
n=in;
e=ie;
}
public void process (APDU apdu) {
byte[] buffer = apdu.getBuffer();
//check Select APDU command
if((buffer[ISO7816.OFFSET_CLA] ==0) &&
(buffer[ISO7816.OFFSET_INS] ==(byte) (0xA4)) )
return;
if(buffer[ISO7816.OFFSET_CLA] !=publickey_CLA)
ISOException.throwIt
(ISO7816.SW_CLA_NOT_SUPPORTED);
}
/*read the key back from a string.*/
publickey(String from){
StringTokenizer st=new StringTokenizer(from," ");
owner=st.nextToken();
n=readBI(st.nextToken());
e=readBI(st.nextToken());
}
/*use the key to encrypt a 'message' m. m should be a
number from 1 to n (n not included).
use makemessage to convert your message to a BigInteger.
*/
BigInteger encrypt(BigInteger m){
return m.modPow(e,n);
}
/*make a string from this key.*/
public String toString(){
return owner+" "+printBI(n)+" "+printBI(e);
}
/*help methods for reading and writing:*/
final static int radix=36;
static String printBI(BigInteger b){
return b.toString(radix);
}
static BigInteger readBI(String s){
return new BigInteger(s,radix);
}
/* these methods convert an arbitrary message,
in the form of an array of bytes, to a message
suitable for encryption. To do this random bits
are added (this is needed to make cracking of the
system harder), and it is converted to a BigInteger.*/
BigInteger makemessage(byte[] input){
/*to understand this part of the program,
read the description of the BigInteger constructor
(in the standard java help). */
if(input.length>128 ||
input.length*8+24>=n.bitLength())
return new BigInteger("0"); //error! message to long.
byte[] paddedinput=new byte[n.bitLength()/8-1];
for(int i=0;i<input.length;i++)
paddedinput[i+1]=input;
paddedinput[0]=(byte)input.length;
for(int i=input.length+1;i<paddedinput.length;i++)
paddedinput=(byte)(Math.random()*256);
return new BigInteger(paddedinput);
}
/*the inverse of makemessage.*/
static byte[] getmessage(BigInteger b){
byte[] paddedoutput=b.toByteArray();
byte[] output=new byte[paddedoutput[0]];
for(int i=0;i<output.length;i++)
output=paddedoutput[i+1];
return output;
}
}
class privatekey{
/*the data of a key*/
BigInteger n,e,d;
String owner;
int bits;
Random ran;
/*unimportant things, needed for calculations:*/
static int certainty=32;
static BigInteger one=new BigInteger("1"),
three=new BigInteger("3"),
seventeen=new BigInteger("17"),
k65=new BigInteger("65537");
/*make a new key. supply the name of the owner of the
key, and the number of bits.
owner: all spaces will be replaced with underscores.
bits: the more bits the better the security. Every
value above 500 is 'safe'. If you are a really paranoid
person, you should use 2000.*/
privatekey(String iowner,int ibits){
BigInteger p,q;
bits=ibits;
owner=iowner.replace(' ','_');//remove spaces from owner name.
ran=new Random();
p=new BigInteger(bits/2,certainty,ran);
q=new BigInteger((bits+1)/2,certainty,ran);
n=p.multiply(q);
BigInteger fi_n=fi(p,q);
e=chooseprimeto(fi_n);
d=e.modInverse(fi_n);
}
/*read the key back from a string*/
privatekey(String from){
StringTokenizer st=new StringTokenizer(from," ");
st.nextToken();
n=readBI(st.nextToken());
e=readBI(st.nextToken());
d=readBI(st.nextToken());
}
/*some help methods:*/
static BigInteger fi(BigInteger prime1,BigInteger prime2){
return prime1.subtract(one).multiply(prime2.subtract(one));
}
static BigInteger BI(String s)
{return new BigInteger(s);}
BigInteger chooseprimeto(BigInteger f){
/*returns a number relatively prime to f.
this number is not chosen at random, it first
tries a few primes with few 1's in it. This
doesn't matter for security, but speeds up computations.*/
if(f.gcd(three).equals(one))
return three;
if(f.gcd(seventeen).equals(one))
return seventeen;
if(f.gcd(k65).equals(one))
return k65;
BigInteger num;
do{
num=new BigInteger(16,ran);
}while(!f.gcd(num).equals(one));
return num;
}
final static int radix=36;
static String printBI(BigInteger b){
return b.toString(radix);
}
static BigInteger readBI(String s){
return new BigInteger(s,radix);
}
/*********************************************/
/*returns the public key of this private key.*/
publickey getpublickey(){
return new publickey(owner,n,e);
}
/*the same encryption that the public key does.*/
BigInteger encrypt(BigInteger m){
return m.modPow(e,n);
}
/*decryption is the opposite of encryption: it
brings the original message back.*/
BigInteger decrypt(BigInteger m){
return m.modPow(d,n);
}
public String toString(){
return owner+" "+printBI(n)+" "+printBI(e)+" "+printBI(d);
}
/*this main demonstrates the use of this program.*/
public static void main(String[] ps){
say("************ make key:");
privatekey priv=new privatekey("sieuwert",92);
publickey pub=priv.getpublickey();
say("the public key:"+priv);
say("************ encrypt message:");
byte[] P="RUOK?".getBytes();
BigInteger Pc=pub.makemessage(P);
say("converted:\t"+printBI(Pc));
BigInteger C=pub.encrypt(Pc);
say("coded message: "+printBI(C));
say("************ decrypt message:");
BigInteger Pc2=priv.decrypt(C);
say("decoded:\t"+printBI(Pc2));
byte[] P2=publickey.getmessage(Pc2);
say("deconverted: "+new String(P2));
}
static void say(String s){
System.out.println(s);
}
}
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