> 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 exhausti

> 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.pdf https://www.iacr.org/archive/eurocrypt2009/54790136/54790136... [2] https://marc-stevens.nl/p/hashclash/ https://marc-stevens.nl/p/hashclash/