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。