please prefer base 64 over base 32 (was: Re: [p2p-hackers] Bitzi (was Various identifier choices))

[hal at finney.org]

Zooko writes:
> Since mojoids include 160-bit SHA1 hashes, they are collision free *even* if
> you base64 encode them and then merge all the upper/lowercase!  (That isn't
> obvious, but once upon a time I convinced myself of it.  I can find the message
> in old mojonation-devel archives if you like.)

Base64 encoding a 160 bit hash would take 26-27 characters.  Compressing
case throws away 1 bit per character that happens to be alphabetic, and
52/64 of the characters will be alphabetic.  So you'll end up discarding
around 21 bits, giving the hash an effective strength of 139 bits.
That should be amply strong for these purposes.

Hal