Random Secrets in Cryptographic Operations

Often we might need to generate random secrets and use them in cryptographic operations when we are implementing cryptographic protocols.

For an example, I recently had to implement Zero Knowledge Protocol with Pedersen Commitment where I need to generate a random secret and convert it to a BigInteger in order to compute the pedersen commitment.  

In this simple post, I thought of noting down the way I found how to do it in Java.

First, we can generate a random secret using "SecureRandom" in java. The article: "Proper Use of Java's SecureRandom" explains how to use SecureRandom properly in order to get it working in a uniform way across different platforms. 
In our example, we generate the random secret by feeding a pre-defined seed - our secret - into the pseudo random number generator of the SecureRandom, so that we can generate the same random secret at a later time as well.

Next, we can convert it to a BigInteger value so that we can use it in cryptographic computations.

Following code shows how the above two steps are implemented:

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;

public class Test {
    public static void main(String[] args) throws NoSuchProviderException, NoSuchAlgorithmException,
                                                  UnsupportedEncodingException {
        String password = "secret";
        //generate random secret using password as the seed
        SecureRandom randSec = SecureRandom.getInstance("SHA1PRNG", "SUN");
        randSec.setSeed(password.getBytes("us-ascii"));

        //create BigInteger of length 256 from the output of the SecureRandom's pseudo random number generator
        BigInteger randSecBI = new BigInteger(256, randSec);

    }
}