Cryptographic Applications - Introduction to Cryptography with Java Applets - page 302

The ShadowBuilder class definition follows:
import java.math.*;
import java.security.*;
public class ShadowBuilder {
//The shadows
BigInteger[] shadow;
//The moduli
//The i-th modulus is for the i-th shadow
BigInteger[] modulus;
//Two other values needed to reconstruct the master key
BigInteger randomMultiplier;
BigInteger reconstructingPrime;
//This constructor accepts the master key, the number of shadows to
//generate, and the tolerance to set for the primes. These will be
//used for the moduli, rather than a set of pairwise relatively prime
//integers. The minimum number of shadows required to reconstruct
//is set at r/2+1.
public ShadowBuilder(BigInteger K, int r, int primeTolerance) {
int s=r/2+1;
int KeySize=K.bitLength();
//Generate a probable prime reconstructingPrime larger than K
SecureRandom sr=new SecureRandom();
reconstructingPrime=new BigInteger(KeySize+1,primeTolerance,sr);
//Generate r primes for the moduli
modulus=new BigInteger[r];
for (int index=0;index<r;index++) {
modulus[index]=new BigInteger(KeySize+2,primeTolerance,sr);
}
//Choose a random multiplier less than the product of any s of the primes.
//This will be so if the bitlength is less than (s-1)*(KeySize-1).
randomMultiplier=new BigInteger(s*(KeySize-1)-KeySize-1,sr);
//Compute K0=K+randomMultiplier*reconstructingPrime
BigInteger K0=K.add(randomMultiplier.multiply(reconstructingPrime));
//Generate the r shadows
shadow=new BigInteger[r];
for (int index=0;index<r;index++) {
shadow[index]=K0.mod(modulus[index]);
}
}
//Methods to return the values the constructor generated.