Add lua script for proxying ZRTP SAS values to legacy phones

Ken is creating a bump-in-the-wire box for legacy IP phones and might
find this script useful.

scripts/lua/zrtp_sas_proxy.lua

+-- zrtp_sas_proxy.lua
+--
+-- Copyright (c) 2011-2013 Travis Cross
+--
+-- Permission is hereby granted, free of charge, to any person obtaining a copy
+-- of this software and associated documentation files (the "Software"), to deal
+-- in the Software without restriction, including without limitation the rights
+-- to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+-- copies of the Software, and to permit persons to whom the Software is
+-- furnished to do so, subject to the following conditions:
+--
+-- The above copyright notice and this permission notice shall be included in
+-- all copies or substantial portions of the Software.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+-- THE SOFTWARE.
+--
+--
+-- When we're acting as a ZRTP man-in-the-middle, proxy the SAS (Short
+-- Authentication String) from one leg of the call to the other.
+--
+-- This script should be called asynchonously with luarun.  e.g.:
+--
+-- <action application="export" data="nolocal:api_on_answer=luarun zrtp_sas_proxy.lua ${uuid}"/>
+--
+aleg=argv[1]
+api=freeswitch.API()
+
+function log(level,msg) return freeswitch.consoleLog(level,"zrtp_sas: "..msg.."\n") end
+function sleep(sec) return freeswitch.msleep(sec*1000) end
+function ready() return api:execute("uuid_exists",aleg)=="true" end
+function getvar(uuid,var)
+  local x=api:execute("uuid_getvar",uuid.." "..var)
+  if x=="_undef_" then return nil end
+  return x
+end
+function getvarp(uuid,var) return getvar(uuid,var)=="true" end
+function display(uuid,msg)
+  local cidn=getvar(uuid,"caller_id_name")
+  return api:execute("uuid_display",uuid.." "..msg.." "..cidn)
+end
+
+function mk_sas(sas1,sas2)
+  if sas1 and sas2 then return sas1.." "..sas2
+  else return sas1 or sas2 or "" end
+end
+
+function get_sas(uuid)
+  return mk_sas(getvar(uuid,"zrtp_sas1_string_audio"),
+                getvar(uuid,"zrtp_sas2_string"))
+end
+
+function log_sas(leg,uuid)
+  return log("notice",leg..": "..uuid.." sas: "..get_sas(uuid))
+end
+
+function display_sas(to,from)
+  return display(to," ("..get_sas(from)..")")
+end
+
+function get_bleg(aleg)
+  local retries=15 bleg=nil
+  while ready() do
+    if retries<1 then return nil end
+    local bleg=getvar(aleg,"signal_bond")
+    if bleg then return bleg end
+    log("debug","waiting for bleg uuid...")
+    sleep(1)
+    retries=retries-1
+  end
+end
+
+function handle_sas(aleg,bleg)
+  local retries=45 af=false bf=false
+  while ready() do
+    if retries<1 then return nil end
+    if not af and getvarp(aleg,"zrtp_secure_media_confirmed_audio") then
+      af=true
+      log_sas("aleg",aleg)
+      display_sas(bleg,aleg)
+    end
+    if not bf and getvarp(bleg,"zrtp_secure_media_confirmed_audio") then
+      bf=true
+      log_sas("bleg",bleg)
+      display_sas(aleg,bleg)
+    end
+    if (af and bf) then break
+    elseif af then log("debug","waiting on bleg zrtp...")
+    elseif bf then log("debug","waiting on aleg zrtp...")
+    else log("debug","waiting for zrtp...") end
+    sleep(1)
+    retries=retries-1
+  end
+end
+
+if not (getvarp(aleg,"zrtp_passthru") or getvarp(aleg,"proxy_media")) then
+  handle_sas(aleg,get_bleg(aleg))
+end