# -*- coding: binary -*- module Rex module Proto module ACPP # From what I've been able to gather from the very limited findings on the # web about this protocol, playing with it against a real Airport device and # referencing the airport-utils package in Debian/Ubuntu, the format of (at # least) the login message is: # # acpp # the header tag, always exactly acpp (4 bytes) # unknown1 # unknown 4-byte field. Almost always 0x00000001 # messageChecksum # checksum of the message, 4 bytes # payloadChecksum # checksum of the payload, 4 bytes # payloadSize # size of the payload, 4 bytes # unknown2 # unknown 8-byte field. probably some sort of # request/response identifier. generally 0 for requests, 1 for replies # messageType # the type of message, 4 bytes. see below. # status # the status of this message, 4 bytes. # generally 0 for success and !0 for failure. # unknown3 # unknown 12-byte field, seemingly always 0. Probably 'reserved' # password # 32-byte password, 'encrypted' by XOR'ing it with a 256-byte static key (see XOR_KEY) # unknown4 # unknown 48-byte field, always 0. # # There are several possible message types: # # * 20 -- retrieve settings (payload is some list of settings to obtain) # * 21 -- update setttings (and if the 'acRB' setting is set, it reboots) # * 3 -- Upload firmware # # TODO: if you find more, add them above. # # When the message type is anything other than 20 or 3, payloadSize is set to -1 and # payloadChecksum is set to 1. It may be a bug that 21 doesn't look at the # checksum. Adler32 is used to compute the checksum. # # The message payload is a bit of an unknown right now, as it *seems* like # the payload always comes in a subsequent request. Simply appending # a payload to the existing message does not appear to work (but this needs # more testing) # This was taken from airport-util's AirportInforRecord for ease of copying, but can # also be obtained by XOR'ing the null-padded known plain text with the appropriate 32-byte # ciphertext from an airport-util request XOR_KEY = [ 14, 57, -8, 5, -60, 1, 85, 79, 12, -84, -123, 125, -122, -118, -75, 23, 62, 9, -56, 53, -12, 49, 101, 127, 60, -100, -75, 109, -106, -102, -91, 7, 46, 25, -40, 37, -28, 33, 117, 111, 44, -116, -91, -99, 102, 106, 85, -9, -34, -23, 40, -43, 20, -47, -123, -97, -36, 124, 85, -115, 118, 122, 69, -25, -50, -7, 56, -59, 4, -63, -107, -113, -52, 108, 69, -67, 70, 74, 117, -41, -2, -55, 8, -11, 52, -15, -91, -65, -4, 92, 117, -83, 86, 90, 101, -57, -18, -39, 24, -27, 36, -31, -75, -81, -20, 76, 101, -35, 38, 42, 21, -73, -98, -87, 104, -107, 84, -111, -59, -33, -100, 60, 21, -51, 54, 58, 5, -89, -114, -71, 120, -123, 68, -127, -43, -49, -116, 44, 5, -3, 6, 10, 53, -105, -66, -119, 72, -75, 116, -79, -27, -1, -68, 28, 53, -19, 22, 26, 37, -121, -82, -103, 88, -91, 100, -95, -11, -17, -84, 12, 37, 29, -26, -22, -43, 119, 94, 105, -88, 85, -108, 81, 5, 31, 92, -4, -43, 13, -10, -6, -59, 103, 78, 121, -72, 69, -124, 65, 21, 15, 76, -20, -59, 61, -58, -54, -11, 87, 126, 73, -120, 117, -76, 113, 37, 63, 124, -36, -11, 45, -42, -38, -27, 71, 110, 89, -104, 101, -92, 97, 53, 47, 108, -52, -27, 93, -90, -86, -107, 55, 30, 41, -24, 21, -44, 17, 69, 95, 28, -68, -107, 77, -74, -70, -123, 39 ].pack("C*") class Message # @return [Integer] the type of this message attr_accessor :type # @return [String] the password to attempt to authenticate with attr_accessor :password # @return [String] the optional message payload attr_accessor :payload # @return [Integer] the status of this message attr_accessor :status def initialize @payload = '' @type = 0 @status = 0 @password = '' @unknown1 = 1 @unknown2 = '' @unknown3 = '' @unknown4 = '' end # Determines if this message has a successful status code # # @return [Boolean] true iff @status is 0, false otherwise def successful? @status == 0 end # Get this Message as a String # # @return [String] the string representation of this Message def to_s with_checksum(Zlib.adler32(with_checksum(0))) end # Compares this Message and another Message for equality # # @param other [Message] the Message to compare # @return [Boolean] true iff the two messages are equal, false otherwise def ==(other) other.type == @type && other.status == @status && other.password == @password && other.payload == @payload end # Decodes the provided data into a Message # # @param data [String] the data to parse as a Message # @param validate_checksum [Boolean] true to validate the message and # payload checksums, false to not. Defaults to true. # @return [Message] the decoded Message def self.decode(data, validate_checksum = true) data = data.dup fail "Incorrect ACPP message size #{data.size} -- must be 128" unless data.size == 128 fail 'Unexpected header' unless 'acpp' == data.slice!(0, 4) _unknown1 = data.slice!(0, 4) read_message_checksum = data.slice!(0, 4).unpack('N').first read_payload_checksum = data.slice!(0, 4).unpack('N').first _read_payload_size = data.slice!(0, 4).unpack('N').first _unknown2 = data.slice!(0, 8) type = data.slice!(0, 4).unpack('N').first status = data.slice!(0, 4).unpack('N').first _unknown3 = data.slice!(0, 12) password = Rex::Encoding::Xor::Generic.encode(data.slice!(0, 32), XOR_KEY).first.strip _unknown4 = data.slice!(0, 48) payload = data m = new m.type = type m.password = password m.status = status m.payload = payload # we can now validate the checksums if desired if validate_checksum actual_message_checksum = Zlib.adler32(m.with_checksum(0)) if actual_message_checksum != read_message_checksum fail "Invalid message checksum (expected #{read_message_checksum}, calculated #{actual_message_checksum})" end # I'm not sure this can ever happen -- if the payload checksum is wrong, then the # message checksum will also be wrong. So, either I misunderstand the protocol # or having two checksums is useless actual_payload_checksum = Zlib.adler32(payload) if actual_payload_checksum != read_payload_checksum fail "Invalid payload checksum (expected #{read_payload_checksum}, calculated #{actual_payload_checksum})" end end m end def with_checksum(message_checksum) [ 'acpp', @unknown1, message_checksum, Zlib.adler32(@payload), @payload.size, @unknown2, @type, @status, @unknown3, Rex::Encoding::Xor::Generic.encode([@password].pack('a32').slice(0, 32), XOR_KEY).first, @unknown4, payload ].pack('a4NNNNa8NNa12a32a48a*') end end end end end