今天做的模块又用到了Hash函数，突然想起Hash函数可能会比较占CPU资源，所以希望使用一种速度最快的摘要函数。但是PHP中的Hash函数很多，MD4、MD5、SHA-1、SHA-256、SHA-384以及SHA-512，都是比较常见的安全领域的HASH应用。于是写了个程序对比了一下PHP支持的各种Hash函数：
<?php
define('testtime', 50000);
$algos = hash_algos();
foreach($algos as $algo) {
$st = microtime();
for($i = 0; $i < testtime; $i++) {
hash($algo, microtime().$i);
}
$et = microtime();
list($ss, $si) = explode(' ', $st);
list($es, $ei) = explode(' ', $et);
$time[$algo] = $ei + $es - $si - $ss;
}
asort($time, SORT_NUMERIC);
print_r($time);
?>
此程序测试每种hash函数支持的算法，对50000个字符串执行hash计算，然后将耗时按从低到高排序，结果如下：
Array
(
[crc32b] => 1.14942403926
[crc32] => 1.15080493481
[adler32] => 1.17250810205
[md4] => 1.21484698894
[md5] => 1.25582505324
[sha256] => 1.31992111638
[ripemd256] => 1.34005199425
[ripemd128] => 1.34174097336
[sha1] => 1.34424093234
[ripemd160] => 1.36161398381
[haval128,3] => 1.37490507759
[haval160,3] => 1.37925811601
[haval192,3] => 1.37971906387
[haval224,3] => 1.38690299403
[haval256,3] => 1.38968507692
[tiger128,3] => 1.40321999939
[tiger192,3] => 1.42025405684
[tiger160,3] => 1.42113689062
[ripemd320] => 1.42461802158
[haval128,4] => 1.4465580045
[haval160,4] => 1.44935391309
[haval192,4] => 1.45606506625
[haval224,4] => 1.4650528846
[tiger128,4] => 1.47951410777
[tiger192,4] => 1.49081709387
[haval256,4] => 1.50713596634
[haval160,5] => 1.51613600436
[haval224,5] => 1.51645894888
[haval192,5] => 1.51678603177
[haval256,5] => 1.51900808377
[tiger160,4] => 1.52507308815
[haval128,5] => 1.53689793875
[whirlpool] => 1.82801189377
[snefru] => 1.85931909387
[gost] => 1.89863007236
[sha384] => 1.95804009064
[sha512] => 1.97130295938
[md2] => 4.99702701607
)
CRC是冗余验证算法，不适合用来做唯一标识符Hash计算，MD4是最快的摘要算法，MD5次之，SHA系列算法居然是SHA-256最快，比SHA-1还快一些。由此得出结论：要把唯一标识符转换成定长字串可以考虑使用MD4，而密码加密则SHA-1或SHA-256更合适。MD5就没有多少使用的必要了，速度比不过MD4，安全性比不过SHA，还是趁早放弃的好。