gpg-auth-import.rb

#!/usr/bin/env ruby

# create temporary auth key first via gui, then export your whole keyring and modify it

require 'digest'

unpatched = File.read 'temp_auth.key'

unpatched_bytes = unpatched.bytes

packets = []

until unpatched_bytes.empty?
  tag = unpatched_bytes.shift

  case (tag & 0x03)
  when 0
    length = unpatched_bytes.shift(1)
    count = length[0]
  when 1
    length = unpatched_bytes.shift(2)
    count = length.pack('CC').unpack('n')[0]
  end

  body = unpatched_bytes.shift(count)

  packet = [tag, length, body]

  packets << packet
end

fail unless packets.count == 5

# primary key

primary_key = packets[0]

length = primary_key[1]
length.unshift(0) unless length.count == 2

primary_key[0] = 0x99

# subkey

subkey = packets[3]

length = subkey[1]
length.unshift(0) unless length.count == 2

subkey[0] = 0x99

# signature

sig = packets[4][2]

hashed_subpacket_data_count = sig[4..5].pack('CC').unpack('n')[0]

sig = sig[0,6+hashed_subpacket_data_count]

# trailer

trailer = [0x04, 0xFF, sig.length]

trailer.insert(2, 0) until trailer.length == 6

# hashyay

bytes_to_hash = [primary_key, subkey, sig, trailer]

to_hash = bytes_to_hash.flatten.pack('c*')

sha256 = Digest::SHA256.new

sha256.update to_hash

p sha256.hexdigest