elgamalverify.java

ElGamal method is an aymetric method to crypt message. You can use ElGamal to crypt the key session

package elgamal;
import java.math.BigInteger;

public class ElGamalVerify {
    private boolean accept;
    public ElGamalVerify(Parameter params,PublicKey y,byte[]M,BigInteger r,BigInteger s){
        
        sha256 sh=new sha256(M);
        int[]sha=sh.getHash();
        byte[]hash=new byte[32];
        int i=0;
        for(int j=0;j<8;j++){
            hash[i++]=(byte)(sha[j] & 0xFF);
            hash[i++]=(byte)((sha[j]>>>8) & 0xFF);
            hash[i++]=(byte)((sha[j]>>>16) & 0xFF);
            hash[i++]=(byte)((sha[j]>>>24) & 0xFF);
        }
        BigInteger m=new BigInteger(hash);
        BigInteger p1=params.getP();
        if(r.compareTo(p1)>=0)accept=false;
        else{
           BigInteger u1=y.getY().modPow(r, params.getP()).multiply(r.modPow(s, params.getP())).mod(params.getP());
           BigInteger u2=params.getG().modPow(m, params.getP());
           if(u1.compareTo(u2)==0)accept=true;
           else accept=false;
        }
        
    }
    
    public boolean getVerify(){
        return accept;
    }
    
}