Thank you for getting this off the ground! In doing some playing around I noticed that I got different results when I used a custom alphabet using your library than through the Javascript or Ruby versions.

I used this codepen from Ivan Akimov to test the JS version:
https://codepen.io/ivanakimov/pen/bNmExm

ID: 1 / salt: 'salt' / no custom alphabet - OK
Javascript: XG
Ruby: XG
PL/SQL: XG

ID: 1 / min_length: 6 / salt: 'salt' / no custom alphabet - OK
Javascript: xkXG8Z
Ruby: xkXG8Z
PL/SQL: xkXG8Z

ID: 1 / min_length: 6 / salt: 'salt' / alphabet: 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' - ERROR
Javascript: MEPWMP
Ruby: MEPWMP
PL/SQL: JPRAPM

I wish I could offer more assistance.