PHP expresses two different strings to be the same [duplicate]

ctf遇到一题，绕过 == 操作符判断的 php:md5 相等验证原理在 stackoverflow上找到了答案stackoverflow php-expresses-two-different-strings-to-be-the-same  why-md5240610708-is-equal-to-md5qnkcdzoWhy does the following statement return 

true

?

"608E-4234" == "272E-3063"

"608E-4234"

 isthe float number format, so they will cast into number when they compares.

608E-4234

 and 

272E-3063

 willboth be 

float(0)

 becausethey are too small.For 

==

 inphp,If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically.http://php.net/manual/en/language.operators.comparison.phpand

var_dump(md5('240610708') == md5('QNKCDZO'));

Output:

bool(true)

md5('240610708')  'sresult is  0e462097431906509019562988736854 . md5('QNKCDZO')  'sresult is  0e830400451993494058024219903391 .They are both float number format strings (numerical strings), and if you use  ==  inphp, when compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically.Both of the strings are converted to  0  whencompared with  == ,if you want to compare them as string, remember to use  === (strictcomparison) instead.

类似

PHP 探测任意网站密码明文/加密手段办法： md5('240610708') == md5('QNKCDZO')

var_dump(md5('240610708') == md5('QNKCDZO'));var_dump(md5('aabg7XSs') == md5('aabC9RqS'));var_dump(sha1('aaroZmOk') == sha1('aaK1STfY'));var_dump(sha1('aaO8zKZF') == sha1('aa3OFF9m'));var_dump('0010e2' == '1e3');var_dump('0x1234Ab' == '1193131');var_dump('0xABCdef' == ' 0xABCdef');https://news.ycombinator.com/item?id=9484757