Please understand that "to hash" is quite different from "to encrypt". Yes, one can build a cipher from secure hashes. But that's not what is going on here, and crc32 is in no way a secure hash, quite aside from the fact that a security parameter of 32 bits is easily bruted.

How do I fix this?

Read Crypto Eng. or a similar reference, and rethink your approach to the business problem. You want to bring relevant cryptographic primitives to bear upon it.