What is a 76-step SHA1 collision? From Twitter:


  Marc Stevens released a new 76-step (out of 80) SHA-1 collision, and SIMD libdetectcoll https://marc-stevens.nl/research/ 


What is a 76-step collision, and how does it differ from a "regular" collision? Is it related to whatever a "freestart" collision is?
Analysis of a primitive often times is conducted on a reduced strength variant of the actual algorithm. This makes it easier to find the weak points of the design, which can become obscured after many iterations.

Assuming a "regular" collision means a collision over the entire 80 rounds, then a 76-step collision finds a collision after 76 rounds. 

The paper for the result in question does mention that it is for a free-start collision. As for what this means, there is a Q/A here that does a goob job of explaining. Basically, it means that the attacker is allowed to select the initialization vector.