How can a collision attack using MD5 be used to break WOTS

Question

It is stated in Winternitz One time signature security that MD5 is not safe for Winternitz due to collision attack. Given that WOTS generates multiple, say 32 private keys then hashing them a number of times to obtain 32 public keys. How does a collision attack from MD5 break the Winternitz OTS? Does this mean I have to find 32 collisions of MD5 ?

Answer 1

I believe that, in the question you cited, the answer included:

BTW: this appears to be more about the proof technique used to prove W-OTS, rather than the actual security; we can create MD5 collisions (invalidating the proof), however we don't know how to use those collisions to actually attack W-OTS-MD5; hence it would appear to be secure (but we can't prove it).

That is, we don't know how a collision attack would break Winternitz; we just can't prove that it can't.