RE: CBV

> From: Seth Goodman
> Sent: Friday, April 30, 2004 10:24 AM

<...>

> If we want to use the header protecting hash as a unique message
> ID, it will
> have to be longer.  Let's say a given mailer sends out 16 million messages
> per day.  That is 2^24, and considering the birthday bound, you would need
> about 48 bits of hash to avoid a collision in a single day's message
> traffic.  That amounts to eight base 64 characters instead of four, which
> reduces the maximum local-part length from 46 to 42 characters before
> breaking the 64-character local-part limit.

Actually, we can accomplish the same thing by simply concatenating the two
shorter hashes.  Since the header protection hash will be different for
every message we send due to the date header changing, the outer hash will
also change.  We should get confirmation that there are no hidden issues
with this from someone who is more expert on crypto than I, but it at least
sounds feasible.  Since SHA-1 has such good randomizing behavior, I think it
stands a good chance of passing cryptographic muster.

--

Seth Goodman