php hash('crc32') and crc32() return different value

Question

i want to ask about PHP crc32 hashing. i'm tried using hash('md5','value') and md5('value') its return same output.

output : 2063c1608d6e0baf80249c42e2be5804

but when i'm try to use hash('crc32','value') and crc32('value') its return different output.

hash() output : e0a39b72

crc32() output : 494360628

anyone know why it can return a different output?

thanks :)

That's because one is a hash and one calculates the polynomial of a string... — Andrei, Nov 22 '16 at 12:21

score 5 · Accepted Answer · edited May 23 '17 at 11:47

5

hash("crc32b", $str) will return the same string as str_pad(dechex(crc32($str)), 8, '0', STR_PAD_LEFT).

See manual and also about difference between crc32 and crc32b

edited May 23 '17 at 11:47

Community

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answered Nov 22 '16 at 12:24

Timurib

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Instead of `str_pad(..., 8, '0', STR_PAD_LEFT)` you can do `sprintf('%08s', ...)` – Gras Double Dec 20 '17 at 00:38

Xorifelse · Answer 2 · 2017-09-22T15:38:50.237

There are minor differences between them, first of all crc32() uses the hashing algorithm crc32b and crc32() returns an integer unlike hash() that returns a hexadecimal value.

$str = 'testing';

$hex = hash('crc32b',$str); // e8f35a06
$dec = crc32($str);         // 3908262406

echo dechex($dec) == $hex; // true, both value e8f35a06
echo hexdec($hex) == $dec; // true, both value 3908262406

Keep in mind that the values differ on 32 and 64 bit environments.

score 3 · Answer 3 · answered Nov 22 '16 at 23:32

What PHP calls crc32(...) or hash("crc32b", ...) (one returning an integer, the other a string) is the standard PKZip/ITU-T V.42 CRC-32. What PHP calls hash("crc32", ...), oddly using the same name as the incompatible PHP crc32() function, is different, and is the BZIP2 CRC-32.

php hash('crc32') and crc32() return different value

3 Answers3