I understand the case for Base91, but why hex over Base64? Base64 for readability and sticking to multiples of two, Base91 for maximum efficiency with readable ASCII.
Base 64 is good at nothing and bad at some things.
- Hex is human readable, case insensitive, not that "inefficient", and always aligns to bytes.
- Base 85 and basE91 are efficient.
- Bitcoin uses Base58 because they thought base 64 was too human unreadable. Ethereum uses Hex.
- Base 256 (bytes) is efficient and the native language of computers.
Base 64 is not efficient, not human readable, and not easy to encode.
The biggest problem with base 64 is that base 64 is not base 64. Are you doing base 64 with padding? Are you doing base 64 with URL safe characters or URL unsafe characters? Are you following the standard RFC 4648 bucket encoding, or are you using iterative divide by radix? I think a great place where the cracks show is JOSE, where for things like thumbprints there's a ton of conversion steps (UTF-8 key -> base 64 -> ASCII bytes -> digest (bytes) -> base 64 thumbprint).
My personal advise for 90% of projects considering looking at base 64 should just use Hex or bytes. If needing human readability, use Hex. Otherwise use binary.
