Why would you use a MAC at all here? There is no secret. The hash comes from the "secure" server. What they needed was a plain old hash, not a (H)MAC. This is j

Why would you use a MAC at all here? There is no secret. The hash comes from the "secure" server. What they needed was a plain old hash, not a (H)MAC. This is just an integrity check. Also, MD5 isn't broken for second preimage attacks. People like to repeat the blanket statement that MD5 is trivially broken, but in this case, it isn't. Still, it wouldn't be advisable to use here because it's broken in enough other scenarios that it makes people uncomfortable in general now. If they did use MD5, it's still a nation-state or significant crypto breakthrough before anyone could attack it.