Is there a way to generate n strings with the same MD5 hash?


1 Answer 1


MD5 is a Merkle–Damgård hash, so it's vulnerable to the length extension attack.

That means there's a simple way to find multicollisions using any algorithm that can find collisions for an arbitrary IV:

  1. Find some collision $\operatorname{MD5}(a) = \operatorname{MD5}(b)$ using the normal IV.
  2. Find another collision $\operatorname{MD5}'(c) = \operatorname{MD5}'(d)$ using the output from the first step as IV.
  3. Combine them to valid messages that look like $a||c$, $a||d$, $b||c$ and $b||d$, except for the padding. This may require adding one more (equal) message block to get a valid padding and length.

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