duanrenchuo9244
2014-07-09 11:05
浏览 80
已采纳

PHP - Glitchy mod(%)运算符

For some reason: the display looks like this:

3 to the power of x mod 17 is 19. This is called v.

Shared person a (v):
19 

and in the script, it looks like this (this script is used to describe Diffie-Hellman key exchange algorithm.):

$p="17";
$g="3";
$px=gmp_nextprime(rand());
$x=gmp_strval($px);
$a=$g^$x%$p;
echo "$g to the power of x mod $p is $a. This is called v.<br>";
echo "<br>Shared person a (v):<br>";
echo "$a <br>";

Wondering if this is kind of a PHP glitch, because:

if{x mod y=z}, z<y

Now my questions: How to fix this? Had I done anything wrong? Is this a PHP glitch?

(The code needs a clean up, I know.)

Additional notes: $x = 2047401017

  • 写回答
  • 好问题 提建议
  • 关注问题
  • 收藏
  • 邀请回答

2条回答 默认 最新

  • dongzuoyue6556 2014-07-09 11:12
    已采纳

    Well, ^ is not the power operator and modulo precedes both of them; besides, GMP has a function for power-modulo already:

    $p="17";
    $g="3";
    $px=gmp_nextprime(rand());
    
    $a = gmp_powm($g, $px, $p);
    
    echo "$g to the power of x mod $p is $a. This is called v.<br>";
    echo "<br>Shared person a (v):<br>";
    echo "$a <br>";
    
    已采纳该答案
    评论
    解决 无用
    打赏 举报
  • doxd96148 2014-07-09 11:12

    ^ is not the exponent operator, it's the bitwise XOR operator. As of PHP 5.6, the exponent operator is **. So it should be either

    $a = ($g ** $x) % $p;
    

    or

    $a = $g ** ($x % $p);
    

    The exponent operator was added in PHP 5.6. Prior to this, you need to use the pow() function:

    $a = pow($g, $x) % $p;
    
    评论
    解决 无用
    打赏 举报

相关推荐 更多相似问题