Hash of a string to be of specific length

Question

Is there a way to generate a hash of a string so that the hash itself would be of specific length? I've got a function that generates 41-byte hashes (SHA-1), but I need it to be 33-bytes max (because of certain hardware limitations). If I truncate the 41-byte hash to 33, I'd probably (certainly!) lost the uniqueness.

Or actually I suppose an MD5 algorithm would fit nicely, if I could find some C code for one with your help.

EDIT: Thank you all for the quick and knowledgeable responses. I've chosen to go with an MD5 hash and it fits fine for my purpose. The uniqueness is an important issue, but I don't expect the number of those hashes to be very large at any given time - these hashes represent software servers on a home LAN, so at max there would be 5, maybe 10 running.

Answer 1

If I truncate the 41-byte hash to 33, I'd probably (certainly!) lost the uniqueness.

What makes you think you've got uniqueness now? Yes, there's clearly a higher chance of collision when you're only playing with 33 bytes instead of 41, but you need to be fully aware that collisions are only ever unlikely, not impossible, for any situation where it makes sense to use a hash in the first place. If you're hashing more than 41 bytes of data, there are clearly more possible combinations than there are hashes available.

Now, whether you'd be better off truncating the SHA-1 hash or using a shorter hash such as MD5, I don't know. I think I'd be more generally confident when keeping the whole of a hash, but MD5 has known vulnerabilities which may or may not be a problem for your particular application.