PHP: Simple, Validate if string is hex?

Question

I have no clue how to validate this string. I am simply supplying an IV for an encryption, but can find no "is_hex()" or similar function, I can't wrap my head around it! I read on a comment in the php documentation (user contrib. notes) this:

if($iv == dechex(hexdec($iv))) {
  //True
} else {
  //False
}

But that doesn't seem to work at all.. It only says false. If it helps my input of my IV would be this:

92bff433cc639a6d

Answer 1

Is there any reason not to match against a simple RE like "[0-9A-Fa-f]+"? (edit: possibly with a '^' at the beginning and '$' at the end to assure you've matched the whole string).

Answer 2

Maybe this comment will help you:

http://php.net/manual/en/function.http-chunked-decode.php

He provides his is_Hex function.

Answer 3

use function : ctype_xdigit

http://php.net/ctype_xdigit

<?php
$strings = array('AB10BC99', 'AR1012', 'ab12bc99');
foreach ($strings as $testcase) {
    if (ctype_xdigit($testcase)) {
        echo "The string $testcase consists of all hexadecimal digits.\n";
    } else {
        echo "The string $testcase does not consist of all hexadecimal digits.\n";
    }
}
?> 

The above example will output:

The string AB10BC99 consists of all hexadecimal digits.

The string AR1012 does not consist of all hexadecimal digits.

The string ab12bc99 consists of all hexadecimal digits.

Answer 4

Your input is too large. From the PHP manual of dexhex

The largest number that can be converted is 4294967295 in decimal resulting to "ffffffff"

So you'll be better off using a RegEx, which have already been supplied here by others.

Answer 5

maybe this helps:

http://codeigniter.com/wiki/hexadecimal_validation/

Answer 6

And because there is always more than one way to do it (even in PHP), you could try something like this:

if ( 0 == strcspn($iv,'0123456789abcdef') ) {
    // TRUE
}
else {
    // FALSE
}

Should be roughly equivalent to, but faster than, preg_match('{[^0-9a-f]}, $iv), although in terms of learninging curves, preg_match is significantly faster to understand ...