primitives.java

RSA is an asymetric method to crypt message. You can use RSA to crypt the key session of symetric me

package rsa;
import java.math.BigInteger;
public class Primitives {
    public Primitives(){
    }
    
    public static String I2OSP(BigInteger x,int xLen){
        String ret=x.toString(16);
        int ret_len=ret.length();
        if(ret_len< (2*xLen)){
            for(int i=0;i<(2*xLen-ret_len);i++)ret="0"+ret;
        }else if(ret_len>2*xLen){
            ret="Integer too large";
        }
        return ret;
    }
    
    public static BigInteger OS2IP(String sx){
        BigInteger x;
        try{
            x=new BigInteger(sx,16);
        }catch(Exception ec){
            x=null;
        }
        return x;
    } 

    public static BigInteger RSAEP(BigInteger n,BigInteger e,BigInteger m){
        BigInteger c;
        if(m.compareTo(n)>=0)c=null;
        else{
            c=m.modPow(e, n);
        }
        return c;
    }
    
    public static BigInteger RSADP(BigInteger n,BigInteger d,BigInteger c){
        BigInteger m;
        if(c.compareTo(n)>=0)m=null;
        else{
            m=c.modPow(d, n);
        }
        return m;
    }
    
    public static BigInteger RSASP1(BigInteger n,BigInteger d,BigInteger m){
        BigInteger s;
        if(m.compareTo(n)>=0)s=null;
        else{
            s=m.modPow(d, n);
        }
        return s;
    }
    
    public static BigInteger RSAVP1(BigInteger n,BigInteger e,BigInteger s){
        BigInteger m;
        if(s.compareTo(n)>=0)m=null;
        else{
            m=s.modPow(e, n);
        }
        return m;
    }
}