mgf.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 MGF {
    private static String T;
    
    public static String getMGF(String msgSeed,long maskLen){
        int hLen=20;
        long hhLen=hLen;
        hhLen<<=32;
        if(maskLen > hhLen)T="mask too long";
        else{
            T="";
            int L=(int)((maskLen+hLen-1)/hLen);
            for(int counter =0;counter <L;counter++){
                String C=Primitives.I2OSP(BigInteger.valueOf(counter),4);
                sha1 sh=new sha1(msgSeed+C,16);
                int[]sha=sh.getHash();
                for(int i=0;i<5;i++)T=T+completeparzero(Long.toHexString(sha[4-i] & 0xFFFFFFFFL),8);
            }
        }
        return T;
    }
    
    private static String completeparzero(String str,int len){
        if(str.length()<len){
            int str_len=str.length();
            for(int i=0;i<len-str_len;i++)str="0"+str;
        }
        return str;
    }

}