A SHA-1 chosen-prefix collision attack
Can collision attacks provide the same size of data? I suspect it would be dramatically more difficult to produce a collision of equal data-size as the original.<p>So perhaps, the easiest way to defend against a collision attack is to transmit the size of the data alongside the checksum. Like a checksum, it is extremely lightweight and easy to check.<p>In my data framework project (where I use sha1 to identify blocks), I've been looking for an excuse to do this, because knowing size of a block is incredibly useful for applying performance heuristics. I suspect it is also a significant defense against collision attacks. Am I wrong?