From 1becf51a5673acf0eab38c2abe568ca23b3da680 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Thu, 20 Feb 2025 09:14:12 +0000
Subject: [5.1] Tickets no longer double encrypted

---
 5.1/charon.rb | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100755 5.1/charon.rb

(limited to '5.1/charon.rb')

diff --git a/5.1/charon.rb b/5.1/charon.rb
new file mode 100755
index 0000000..7a69e39
--- /dev/null
+++ b/5.1/charon.rb
@@ -0,0 +1,80 @@
+#!/usr/bin/env ruby
+
+require 'openssl'
+require 'securerandom'
+require 'sinatra'
+
+Users = {
+  "Athena" => "Passw0rd!"
+}
+
+Services = {
+  "_TGS" => "eiqu@a5ahs8mooqu9Eng",
+  "Mail" => "{FvM<kgG}VpHxKJO;6Zo"
+}
+
+def encrypt(obj, key)
+  cipher = OpenSSL::Cipher::AES.new(256, :CBC).encrypt
+  cipher.key = Digest::SHA2.digest(key)
+  s = cipher.update(obj) + cipher.final
+  s.unpack('H*')[0].upcase
+end
+
+def decrypt(obj, key)
+  ticket = [obj].pack("H*").unpack("C*").pack("c*")
+  cipher = OpenSSL::Cipher::AES.new(256, :CBC).decrypt
+  cipher.key = Digest::SHA2.digest(key)
+  cipher.update(ticket) + cipher.final
+end
+
+def ticket(username, ws_address, service)
+  ts = Time.now.to_i
+  sk = SecureRandom.hex.upcase
+  p = [sk, username, ws_address, service, 28800, ts].join(?\0)
+  s = encrypt(p, Services[service])
+  ["#{sk},#{ws_address},28800,#{ts}", s]
+end
+
+def noleak(msg, ul, ws)
+  puts "Error: #{msg}, returning nonsense to avoid leakage."
+  ticket(SecureRandom.alphanumeric(ul), ws, SecureRandom.alphanumeric(rand(24) + 8))
+end
+
+post '/login' do
+  request.body.rewind
+  data = JSON.parse(request.body.read)
+  next "Invalid request\n" unless data.keys == %w(username)
+  un = data["username"]
+  ul = un.length
+  ws = request.ip
+  next noleak("Invalid username", ul, ws) unless Users.keys.include?(un)
+  anc, tgt = ticket(un, ws, "_TGS")
+  "#{encrypt(anc, Users[un])},#{tgt}"
+end
+
+post '/ticket' do
+  request.body.rewind
+  data = JSON.parse(request.body.read)
+  next "Invalid request\n" unless data.keys.sort == %w(authenticator service ticket username)
+  sk, un, ws, sn, ls, ts = decrypt(data["ticket"], Services["_TGS"]).split(?\0)
+  ls = ls.to_i
+  ts = ts.to_i
+  next "Invalid ticket\n" unless sn == "_TGS"
+  next "Invalid ticket\n" unless un == data["username"]
+  next "Invalid ticket\n" unless ws == request.ip
+  next "Invalid ticket\n" unless Time.now.to_i >= ts
+  next "Ticket expired\n" unless Time.now.to_i < (ts + ls)
+  begin
+    aun, aws, als, ats = decrypt(data["authenticator"], sk).split(?,)
+    als = als.to_i
+    ats = ats.to_i
+  rescue OpenSSL::Cipher::CipherError
+    next "Invalid session key\n"
+  end
+  next "Invalid authenticator\n" unless aun == un
+  next "Invalid authenticator\n" unless aws == ws
+  next "Invalid authenticator\n" unless Time.now.to_i >= ats
+  next "Authenticator expired\n" unless Time.now.to_i < (ats + als)
+  anc, svt = ticket(un, ws, data["service"])
+  "#{encrypt(anc, sk)},#{svt}"
+end
-- 
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