[BBLISA] Backing up sparse files ... VM's and TrueCrypt ... etc

[Edward Ned Harvey]

> use a
> 160byte mac to ensure no collisions 

Actually, I want to say more about this.

There is only one way to guarantee there are no collisions.  The checksum
must be equal or larger than the size of the data.  As long as the checksum
is 1 bit smaller than the data, that guarantees at least one checksum result
must map to at least two combinations of the data input.  Depending on your
checksum algorithm, every possible checksum could possibly be reached by two
of the possible inputs.

So, nobody in their right mind would ever do a checksum with enough
precision to ensure no collisions.  You might as well just store the data
two or more times instead.