I think in these attacks are usually talked about in terms of an arbitrary, not specially selected, message / hash. When wikipedia says "Given a hash value h,

I think in these attacks are usually talked about in terms of an arbitrary, not specially selected, message / hash. When wikipedia says "Given a hash value h, it should be difficult to find ....", "h" there is any arbitrary hash. For example, I can tell you the md5 preimage for 5f4dcc3b5aa765d61d8327deb882cf99. Google can tell you that one. That doesn't mean there's a real preimage attack for md5 since given any arbitrary h, I cannot tell you what hashes to it. > The idea here being that if you take some arbitrary message it's unlikely to produce one of these weaker hashes, but by simply selecting a weak hash directly you can find a message for it. You don't get to select the weak hash, like "5f4dcc3b5aa765d61d8327deb882cf99" in this case, to prove you have a preimage attack.