lib/rex/proto/acpp/message.rb
# -*- 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 settings (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