2factor.rb

require 'uri'
require 'rotp'
require 'rqrcode_png'

key = ROTP::Base32.random_base32
totp = ROTP::TOTP.new(key)
uri = totp.provisioning_uri('hoge@hoge.com')

puts "key:#{key} uri:#{uri}"

qr = RQRCode::QRCode.new(uri, size:8)
png = qr.to_img
png.resize(128, 128).save('qr.png')

decode.rb

require 'rotp'

key = 'boqgsqvnmakpldl6'
totp = ROTP::TOTP.new(key)

puts totp.now