sha1collider

The confusing thing is that the team behind SHAttered did choose a prefix - they just had to choose a common prefix rather than two different prefixes (choosing a common prefix simply changes the initial state used by SHA-1). So I'm hoping that my post clarifies this point a bit. The SHAttered attack (classical collision) can be used in practice - for example, my project https://github.com/nneonneo/sha1collider exploits their collision to turn any two PDFs into documents with identical SHA-1 hashes.

Also relevant, a PDF SHA-1 collider: https://github.com/nneonneo/sha1collider

Shameless plug: I built my own version of this to collide arbitrary PDFs: https://github.com/nneonneo/sha1collider My version is similar to this, but removes the 64kb JPEG limit and allows for colliding multi-page PDFs.