40-bit hash = 7 base64 chars = 8 base32 chars = 10 hex chars
80-bit hash = 14 base64 chars = 16 base32 chars = 20 hex chars
120-bit hash = 21 base64 chars = 24 base32 chars = 30 hex chars
Since SRS recommends four base-64 digits, we're only talking about 24-bit
hashes. Much ado about nothing, as the big guy said.
I believe the recommendation is a *minimum* of four base-64 digits.
I'd vote for five base-32 digits and force everything to lower case for the
hash computation. Upon verification, we'd get full use of the 25-bit hash
with only one extra character in the local part.
25-bit? What are you going to do, throw away the bit or pad the next seven? I
think few implementations take 25-bits for hashing...???
If you go with base32, I'd say go with the multiples of 40-bits: 40, 80, 120...
They form base32 expressions without padding (=), and end on byte boundaries.
Michael R. Brumm