Either a) you don't have a clue about the complexity involved in finding a collision for a specific hash or b) your definition of "reasonable time" is longer than the age of the universe and/or using 100 trillion state of the art GPUs is realistic.

I'm leaning towards option a, you read a blog post once and think you're an expert on cryptography now.

  > the complexity involved in finding a collision for a specific hash

If it can be shown that a preimage collision can be computed in less time than an exhaustive search, the algorithm is generally regarded as having a weakness, even if the given "less time" is still a very very long time.

The theoretical complexity of MD5 is 2^128, but a preimage attack was discovered in 2009 which showed that a collision can be found in 2^123.4. [1]

Collision attacks against MD5 have become more practical, there are even frameworks for it [2]. The complexity of 2^123.4 still makes a preimage attack against MD5 computionally unfeasible, but given that it's been shown to be weaker than its theorerical 2^128, it's possible that MD5 has other weaknesses which would allow the complexity to be reduced to a level that is computationally feasible.

[1] https://www.iacr.org/archive/eurocrypt2009/54790136/54790136...

[2] https://marc-stevens.nl/p/hashclash/

To be fair, pretty much every MD5 discussion I've ever seen or been involved in (including with "security expert" former coworkers) has had someone making the same claim.

What you're describing is the same for every having algorithm in existence. All hashes can represent multiple (indeed, infinite) passwords. So they all have collisions. This is because all hashes are fixed-length, and so finite, while the possible inputs are infinite.

This isn't the reason that MD5 is weaker than other algorithms.

You are describing a first preimage attack. There have not been any computable first (or second) preimage attacks on md5.

https://stackoverflow.com/questions/822638/does-any-publishe...

There are collision attacks, but that is not relevant for password cracking.

From 2009: a preimage attack reduced the complexity from 2^128 to 2^123.4 [1].

It's still a big number, but it's less than the theoretical complexity.

[1] https://www.iacr.org/archive/eurocrypt2009/54790136/54790136...

What I meant by "computable" is something that can be computed with today's hardware.