On Aug 8, 2015, at 12:36 PM, Alec Muffett <alecm@fb.com> wrote:

9) appending a credit-card-like “you typed this properly” extra few characters checksum over the length might be helpful (10..15 bits?) - ideally this might help round-up the count of characters to a full field, eg: XXX in this?

        a1uik-0w1gm-fq3i5-ievxd-m9ceu-27e88-g6o7p-e0rff-dw9jm-ntwkd-sdXXX.onion



For the avoidance of doubt: I am not proposing use of special-case capital letters for checksums.  I merely use capital letters for emphasis. 

—
Alec Muffett
Security Infrastructure
Facebook Engineering
London