package civitas.crypto.parameters;
   
   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.stereotype.Service;
   
   import civitas.crypto.Constants;
   import civitas.crypto.CryptoBase;
   import civitas.util.CivitasBigInteger;
   
  @Service
  public class FindGeneratorService implements Constants {
  	@Autowired
  	CryptoBase cryptoBase;
  
  	public CivitasBigInteger apply(final PrimePair sp) {
  		CivitasBigInteger g = null;
  		boolean reject = false;
  		CivitasBigInteger p = sp.p;
  		CivitasBigInteger negONE = p.subtract(ONE);
  		CivitasBigInteger twoK = p.subtract(ONE).divide(sp.q);
  		do {
  			g = cryptoBase.generateRandomElement(p);
  			g = g.modPow(twoK, p);
  			reject = ONE.equals(g) || g.equals(negONE);
  		} while (reject);
  
  		return g;
  	}
  }