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：

 

 

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。