> > Because MD5 is a relatively weak algorithm, it is possible to create deliberate hash "collisions". That is, take some data and manipulate it until it has th

> > Because MD5 is a relatively weak algorithm, it is possible to create deliberate hash "collisions". That is, take some data and manipulate it until it has the same MD5 as a different piece of data. > > First sentence is true. Second sentence is false - that's called a preimage attack. MD5 is broken for collisions, not preimage or second preimage. > > > It is somewhat cheap and easy to produce a file with a specific SHA-1 hash. > > No, that's called a second preimage attack. SHA-1 is broken for collision, not preimage or second preimage. I think that's backwards. Producing a file with a specific SHA-1 hash is a preimage attack while producing a file with the same hash as another file is a second preimage attack. Not that it matters for SHA-1 where both aren't broken yet.