public class DH {
    private int priKey;
    private static int dhP = 99991;
    private static int dhG = 5;

    public DH() {
        Random random = new Random();
        priKey = random.nextInt(10);
        System.out.println("DH 生成的私鑰為 " + priKey);
    }

  /**
   * 獲取DH算法的公鑰
   */
    public int getPubKey() {
        return startPow(dhG, priKey).divideAndRemainder(new BigInteger(String.valueOf(dhP)))[1].intValue();
    }

  /**
  * 獲取DH算法的共享密鑰
  */
    public int getCommonKey(int pubKeyS) {
        //此處的divideAndRemainder 計(jì)算兩個(gè)BigInteger之間的相除，獲得由數(shù)組構(gòu)成的商和余數(shù)
        return startPow(pubKeyS, priKey).divideAndRemainder(new BigInteger(String.valueOf(dhP)))[1].intValue();
    }

   /**
    * 計(jì)算冪次方。因?yàn)橛?jì)算整數(shù)的冪次方可造成最終的數(shù)值超過(guò)Int最大的范圍，導(dǎo)致計(jì)算錯(cuò)誤。所以此處使用BigInteger來(lái)計(jì)算冪次方
    */
    private BigInteger startPow(int a, int b) {
        if (b == 0) {
            return new BigInteger(String.valueOf(1));
        } else {
            return pow(new BigInteger(String.valueOf(a)),b);
        }
    }

    private BigInteger pow(BigInteger a, int b) {
        if (b != 1)
           //multiply 代表乘法。此處使用遞歸計(jì)算a的b次方冪
            return a.multiply(pow(a, b - 1));
        else
            return a;
    }


}