Figured I’d ask if there was anything built into Unity or Mono that would handle this type of encryption. The references I’ve found on the web for writing my own implementation makes me wonder if I use one of those if the company I’m dealing with will be able to decrypt it on their end, as well as whether I’ll be able to decrypt the response if necessary. The MD5 has was almost too easy by comparison 
AES encryption works without a problem. I implemented it basing on Unity 3.x earlier this year for a project to protect user specific data files
also MD5 is no encryption thats hash, thats not decypherable at all as its a one way algorithm.
The ‘weakest level’ would be SHA1, thats at least 2 way