PHP哈希文件，CRC32b或MD5更好？

Question

I want to hash user uploaded files

then save the hash to db

this help me prevent duplicate upload files

I was wondering which hash algorithm should I use

googled someone say crc32b is better and faster then md5

will not have dynamic errors?

if not use hash_file('crc32b') , or md5_file vs sha1_file ?

Answer 1

A CRC-32 is much faster, and can be used to rule out a match in most cases. If you get a hit with a CRC, then you can apply a larger signature to check that it really is a match. Depending on the volume of your traffic, it is quite possible that you will get false-positive matches with just a CRC. Use a SHA-256 to check to see if it really is a match, and only reject on the basis of that.

There is still an extremely small probability that you will get a false-positive with a SHA-256 as well. For your application however, you might just as well accept preventing a user from uploading a genuinely new file in that very rare case.