+--- -*-lua-*-
+---
+--- Wireshark protocol dissector for TrIPE
+---
+--- (c) 2017 Straylight/Edgeware
+---
+
+-------- Licensing notice ---------------------------------------------------
+---
+--- This file is part of Trivial IP Encryption (TrIPE).
+---
+--- TrIPE is free software; you can redistribute it and/or modify
+--- it under the terms of the GNU General Public License as published by
+--- the Free Software Foundation; either version 2 of the License, or
+--- (at your option) any later version.
+---
+--- TrIPE is distributed in the hope that it will be useful,
+--- but WITHOUT ANY WARRANTY; without even the implied warranty of
+--- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+--- GNU General Public License for more details.
+---
+--- You should have received a copy of the GNU General Public License
+--- along with TrIPE; if not, write to the Free Software Foundation,
+--- Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+local tripe = Proto("tripe", "TrIPE VPN")
+
+-----------------------------------------------------------------------------
+--- Configuration handling.
+
+local CONFIG = {
+ -- Information about the configuration variables. This table, when it's
+ -- set up, maps the internal names, which are used to refer to
+ -- configuration variables in the rest of this code, to a little structure:
+ --
+ -- * `var' names the variable, and is the usual key for lookups;
+ --
+ -- * `name' is the label used in the dialogue box;
+ --
+ -- * `type' is the type of variable, currently either `enum' or `int';
+ --
+ -- * `descr' is a longer (but generally fairly useless) description for
+ -- use in a tooltip;
+ --
+ -- * `allowed' is a sequence of allowed values for an `enum' variable;
+ -- and
+ --
+ -- * `min' and `max' are the limits on permitted values for an `int'
+ -- variable (and may be omitted).
+ --
+ -- More slots are added at runtime:
+ --
+ -- * `map' is a table mapping string values to their integer indices, as
+ -- stored in Wireshark's preferences database.
+ --
+ -- Initially, though, the table is given as a sequence, so that the
+ -- preferences can be populated in a consistent (and approximately logical)
+ -- order.
+
+ { var = "bulk", name = "Bulk transform",
+ type = "enum", allowed = { "v0", "iiv", "naclbox" },
+ descr = "Bulk cryptographic transform", default = "v0" },
+ { var = "hashsz", name = "Hash length", type = "int", min = 0,
+ descr = "Hash length (bytes)", default = 20 },
+ { var = "tagsz", name = "Tag length", type = "int", min = 0,
+ descr = "Authentication tag length (bytes)", default = 10 },
+ { var = "ivsz", name = "IV length", type = "int", min = 0,
+ descr = "Initialization vector length (bytes)", default = 8 },
+ { var = "kx", name = "Key-exchange group",
+ type = "enum", allowed = { "dh", "ec", "x25519", "x448" },
+ descr = "Key-exchange group type", default = "dh" },
+ { var = "scsz", name = "Scalar length", type = "int", min = 1,
+ descr = "Scalar field-element length (bytes)", default = 32 },
+}
+
+local C = { } -- The working values of the configuration variables.
+
+local function set_config(k, v)
+ -- Set configuration variable K to the value V.
+ --
+ -- K is a string naming the variable to set. V is the new value, which may
+ -- be a string or a number.
+ --
+ -- For `int' variables, V is converted to a number if necessary, and then
+ -- checked against the permitted bounds.
+ --
+ -- For `enum' variables, things are more complicated. If V is a string,
+ -- it's checked against the permitted values. If V is a number, it's
+ -- converted back into the corresponding string.
+
+ local info = CONFIG[k]
+
+ if info == nil then error("unknown config key `" .. k .. "'") end
+
+ if info.type == "enum" then
+ if type(v) == "number" then
+ local t = info.allowed[v]
+ if t == nil then
+ error(string.format("bad index %d for `%s'", n, k))
+ end
+ v = t
+ else
+ if info.map[v] == nil then
+ error(string.format("bad value `%s' for `%s'", v, k))
+ end
+ end
+
+ elseif info.type == "int" then
+ local n = tonumber(v)
+ if n == nil then error("bad number `" .. v .. "'") end
+ if n ~= math.floor(n) then
+ error("value `" .. v .. "' is not an integer")
+ end
+ if (info.min ~= nil and n < info.min) or
+ (info.max ~= nil and n > info.max)
+ then
+ error(string.format("value %d out of range for `%s'", n, k))
+ end
+ v = n
+ end
+
+ C[k] = v
+end
+
+-- Set up the configuration information. Configure preferences objects on
+-- the dissector. For `enum' variables, build the `map' slots.
+for i, v in ipairs(CONFIG) do
+ local k = v.var
+ CONFIG[k] = v
+ if v.type == "enum" then
+ local tab = { }
+ v.map = { }
+ for i, t in pairs(v.allowed) do
+ v.map[t] = i
+ tab[i] = { i, t, i }
+ end
+ tripe.prefs[k] = Pref.enum(v.name, v.map[v.default], v.descr, tab)
+ elseif v.type == "int" then
+ tripe.prefs[k] = Pref.uint(v.name, v.default, v.descr)
+ end
+end
+
+local function prefs_changed()
+ -- Notice that the preferences have been changed and update `C'.
+
+ for k, _ in pairs(CONFIG) do
+ if type(k) == "string" then set_config(k, tripe.prefs[k]) end
+ end
+end
+tripe.prefs_changed = prefs_changed
+
+-- Populate the configuration table from the stored preferences or their
+-- default values.
+prefs_changed()
+
+-- Now work through arguments passed in on the command line. Annoyingly,
+-- while one can set preferences on the Wireshark command line, these are
+-- done /before/ Lua scripts are loaded, so the silly thing thinks the
+-- preference slots don't exist. So we have to do it a different way.
+for _, arg in ipairs({...}) do
+ local k, v = arg:match("(.+)=(.+)")
+ if k == nil or v == nil then error("bad option syntax `" .. arg .. "'") end
+ se_config(k, v)
+end
+
+-----------------------------------------------------------------------------
+--- Protocol dissection primitives.
+
+local PF = { } -- The table of protocol fields, filled in later.
+
+-- The `dissect_*' functions follow a common protocol. They parse a thing
+-- from a packet buffer BUF, of size SZ, starting from POS, and store
+-- interesting things in a given TREE; when they're done, they return the
+-- updated index where the next interesting thing might be. As a result,
+-- it's usually a simple matter to parse a packet by invoking the appropriate
+-- primitive dissectors in the right order.
+
+local function dissect_wtf(buf, tree, pos, sz)
+ -- If POS is not at the end of the buffer, note that there's unexpected
+ -- stuff in the packet.
+
+ if pos < sz then tree:add(PF["tripe.wtf"], buf(pos, sz - pos)) end
+ return sz
+end
+
+-- Dissect a ciphertext of some particular kind.
+local dissect_ct = { }
+function dissect_ct.naclbox(buf, tree, pos, sz)
+ tree:add(PF["tripe.ciphertext.tag"], buf(pos, 16)); pos = pos + 16
+ tree:add(PF["tripe.ciphertext.seq"], buf(pos, 4)); pos = pos + 4
+ tree:add(PF["tripe.ciphertext.body"], buf(pos, sz - pos))
+end
+function dissect_ct.iiv(buf, tree, pos, sz)
+ tree:add(PF["tripe.ciphertext.tag"], buf(pos, C.tagsz)); pos = pos + C.tagsz
+ tree:add(PF["tripe.ciphertext.seq"], buf(pos, 4)); pos = pos + 4
+ tree:add(PF["tripe.ciphertext.body"], buf(pos, sz - pos))
+end
+function dissect_ct.v0(buf, tree, pos, sz)
+ tree:add(PF["tripe.ciphertext.tag"], buf(pos, C.tagsz)); pos = pos + C.tagsz
+ tree:add(PF["tripe.ciphertext.seq"], buf(pos, 4)); pos = pos + 4
+ tree:add(PF["tripe.ciphertext.iv"], buf(pos, C.ivsz)); pos = pos + C.ivsz
+ tree:add(PF["tripe.ciphertext.body"], buf(pos, sz - pos))
+end
+
+local function dissect_ciphertext(buf, tree, label, pos, sz)
+ -- Dissect a ciphertext, making the whole thing be a little subtree with
+ -- the given LABEL.
+
+ local t = tree:add(PF[label], buf(pos, sz - pos))
+ dissect_ct[C.bulk](buf, t, pos, sz)
+ return pos
+end
+
+local function dissect_packet(buf, tree, pos, sz)
+ return dissect_ciphertext(buf, tree, "tripe.packet.payload", pos, sz)
+end
+
+-- Dissect a group element of some particular kind.
+local dissect_ge = { }
+function dissect_ge.dh(buf, tree, pos, sz)
+ tree:add(PF["tripe.dh.len"], buf(pos, 2))
+ xsz = buf(pos, 2):uint(); pos = pos + 2
+ tree:add(PF["tripe.dh.x"], buf(pos, xsz)); pos = pos + xsz
+ return pos
+end
+function dissect_ge.ec(buf, tree, pos, sz)
+ tree:add(PF["tripe.ec.xlen"], buf(pos, 2))
+ xsz = buf(pos, 2):uint(); pos = pos + 2
+ tree:add(PF["tripe.ec.x"], buf(pos, xsz)); pos = pos + xsz
+ tree:add(PF["tripe.ec.ylen"], buf(pos, 2))
+ ysz = buf(pos, 2):uint(); pos = pos + 2
+ tree:add(PF["tripe.ec.y"], buf(pos, ysz)); pos = pos + ysz
+ return pos
+end
+function dissect_ge.x25519(buf, tree, pos, sz)
+ tree:add(PF["tripe.x25519.x"], buf(pos, 32))
+ return pos + 32
+end
+function dissect_ge.x448(buf, tree, pos, sz)
+ tree:add(PF["tripe.x448.x"], buf(pos, 56))
+ return pos + 56
+end
+
+local function dissect_my_challenge(buf, tree, pos, sz)
+ -- We don't know how long the group element is going to be. We can set the
+ -- length later, but (at least in older versions) it doesn't work so well
+ -- to increase the length, so make it large to start out, and shrink it
+ -- later.
+ local t = tree:add(PF["tripe.keyexch.mychal"], buf(pos, sz - pos))
+ local q = dissect_ge[C.kx](buf, t, pos, sz)
+ t:set_len(q - pos)
+ return q
+end
+
+local function dissect_my_cookie(buf, tree, pos, sz)
+ tree:add(PF["tripe.keyexch.mycookie"], buf(pos, C.hashsz))
+ return pos + C.hashsz
+end
+
+local function dissect_your_cookie(buf, tree, pos, sz)
+ tree:add(PF["tripe.keyexch.yourcookie"], buf(pos, C.hashsz))
+ return pos + C.hashsz
+end
+
+local kx_scsz = { x25519 = 32, x448 = 56 } -- Hardwired scalar sizes.
+local function dissect_check(buf, tree, pos, sz)
+ local scsz = kx_scsz[C.kx] or C.scsz
+ tree:add(PF["tripe.keyexch.check"], buf(pos, scsz))
+ return pos + scsz
+end
+
+local function dissect_reply(buf, tree, pos, sz)
+ return dissect_ciphertext(buf, tree, "tripe.keyexch.reply", pos, sz)
+end
+
+local function dissect_switch(buf, tree, pos, sz)
+ return dissect_ciphertext(buf, tree, "tripe.keyexch.switch", pos, sz)
+end
+
+local function dissect_switchok(buf, tree, pos, sz)
+ return dissect_ciphertext(buf, tree, "tripe.keyexch.switchok", pos, sz)
+end
+
+local function dissect_misc_payload(buf, tree, pos, sz)
+ tree:add(PF["tripe.misc.payload"], buf(pos, sz - pos))
+ return sz
+end
+
+local function dissect_misc_ciphertext(buf, tree, pos, sz)
+ return dissect_ciphertext(buf, tree, "tripe.misc.ciphertext", pos, sz)
+end
+
+-----------------------------------------------------------------------------
+--- The protocol information table.
+
+local PKTINFO = {
+ -- This is the main table which describes the protocol. The top level maps
+ -- category codes to structures:
+ --
+ -- * `label' is the category code's symbolic name;
+ --
+ -- * `subtype' is the field name for the subtype code;
+ --
+ -- * `info' is a prefix for the information column display; and
+ --
+ -- * `sub' is a table describing the individual subtypes.
+ --
+ -- The subtype table similarly maps subtype codes to structures:
+ --
+ -- * `label' is the subtype code's symbolic name;
+ --
+ -- * `info' is the suffix for the information column display; and
+ --
+ -- * `dissect' is a sequence of primitive dissectors to run in order to
+ -- parse the rest of the packet.
+
+ [0] = {
+ label = "MSG_PACKET", subtype = "tripe.packet.type",
+ info = "Packet data",
+ sub = {
+ [0] = { label = "PACKET_IP", info = "encapsulated IP datagram",
+ dissect = { dissect_packet} }
+ }
+ },
+
+ [1] = {
+ label = "MSG_KEYEXCH", subtype = "tripe.keyexch.type",
+ info = "Key exchange",
+ sub = {
+ [0] = { label = "KX_PRECHAL", info = "pre-challenge",
+ dissect = { dissect_my_challenge,
+ dissect_wtf } },
+ [1] = { label = "KX_CHAL", info = "challenge",
+ dissect = { dissect_my_challenge,
+ dissect_your_cookie,
+ dissect_check,
+ dissect_wtf } },
+ [2] = { label = "KX_REPLY", info = "reply",
+ dissect = { dissect_my_challenge,
+ dissect_your_cookie,
+ dissect_check,
+ dissect_reply } },
+ [3] = { label = "KX_SWITCH", info = "switch",
+ dissect = { dissect_my_cookie,
+ dissect_your_cookie,
+ dissect_switch } },
+ [4] = { label = "KX_SWITCHOK", info = "switch-ok",
+ dissect = { dissect_switchok } },
+ }
+ },
+
+ [2] = {
+ label = "MSG_MISC", subtype = "tripe.misc.type",
+ info = "Miscellaneous",
+ sub = {
+ [0] = { label = "MISC_NOP", info = "no-operation (keepalive)",
+ dissect = { dissect_misc_payload } },
+ [1] = { label = "MISC_PING", info = "transport-level ping",
+ dissect = { dissect_misc_payload } },
+ [2] = { label = "MISC_PONG", info = "transport-level ping reply",
+ dissect = { dissect_misc_payload } },
+ [3] = { label = "MISC_EPING", info = "crypto-level ping",
+ dissect = { dissect_misc_ciphertext } },
+ [4] = { label = "MISC_EPONG", info = "crypto-level ping reply",
+ dissect = { dissect_misc_ciphertext } },
+ [5] = { label = "MISC_GREET", info = "greeting",
+ dissect = { dissect_misc_payload } },
+ }
+ }
+}
+
+do
+ -- Work through the master table and build `cattab' and `subtab' tables,
+ -- mapping category and subtype codes to their symbolic names for
+ -- presentation. The `subtab' is a two-level table, needing two layers of
+ -- indexing.
+ local cattab = { }
+ local subtab = { }
+ for i, v in pairs(PKTINFO) do
+ cattab[i] = v.label
+ if v.sub ~= nil then
+ subtab[i] = { }
+ for j, w in pairs(v.sub) do
+ subtab[i][j] = w.label
+ end
+ end
+ end
+
+ local ftab = {
+ -- The protocol fields. This table maps the field names to structures
+ -- used to build the fields, which are then stored in `PF' (declared way
+ -- above):
+ --
+ -- * `name' is the field name to show in the dissector tree view;
+ --
+ -- * `type' is the field type;
+ --
+ -- * `base' is a tweak describing how the field should be formatted;
+ --
+ -- * `mask' is used to single out a piece of a larger bitfield; and
+ --
+ -- * `tab' names a mapping table used to convert numerical values to
+ -- symbolic names.
+
+ ["tripe.type"] = {
+ name = "Message type", type = ftypes.UINT8, base = base.HEX
+ },
+ ["tripe.cat"] = {
+ name = "Message category", type = ftypes.UINT8, base = base.DEC,
+ mask = 0xf0, tab = cattab
+ },
+ ["tripe.packet.type"] = {
+ name = "Packet subcode", type = ftypes.UINT8, base = base.DEC,
+ mask = 0x0f, tab = subtab[0]
+ },
+ ["tripe.packet.payload"] = {
+ name = "Encrypted packet", type = ftypes.NONE
+ },
+ ["tripe.keyexch.type"] = {
+ name = "Key-exchange subcode", type = ftypes.UINT8, base = base.DEC,
+ mask = 0x0f, tab = subtab[1]
+ },
+ ["tripe.keyexch.mychal"] = {
+ name = "Sender's challenge R = r P", type = ftypes.NONE
+ },
+ ["tripe.keyexch.mycookie"] = {
+ name = "Hash of recipient's challenge = H(R, ...)",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.keyexch.yourcookie"] = {
+ name = "Hash of sender's challenge = H(R', ...)",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.keyexch.reply"] = {
+ name = "Encrypted reply = k R'", type = ftypes.NONE
+ },
+ ["tripe.keyexch.switch"] = {
+ name = "Encrypted reply and switch request = k R', H(...)",
+ type = ftypes.NONE
+ },
+ ["tripe.keyexch.switchok"] = {
+ name = "Encrypted switch confirmation = H(...)", type = ftypes.NONE
+ },
+ ["tripe.misc.type"] = {
+ name = "Miscellenaous subcode", type = ftypes.UINT8, base = base.DEC,
+ mask = 0x0f, tab = subtab[2]
+ },
+ ["tripe.misc.payload"] = {
+ name = "Miscellaneous payload",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.misc.ciphertext"] = {
+ name = "Miscellaneous encrypted payload", type = ftypes.NONE
+ },
+ ["tripe.wtf"] = {
+ name = "Unexpected trailing data",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.keyexch.check"] = {
+ name = "Sender's challenge check value = r XOR H(r K', ...)",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.ciphertext.seq"] = {
+ name = "Sequence number", type = ftypes.UINT32, base = base.DEC
+ },
+ ["tripe.ciphertext.iv"] = {
+ name = "Initialization vector", type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.ciphertext.tag"] = {
+ name = "Authentication tag", type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.ciphertext.body"] = {
+ name = "Encrypted data", type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.dh.len"] = {
+ name = "DH group element length",
+ type = ftypes.UINT16, base = base.DEC
+ },
+ ["tripe.dh.x"] = {
+ name = "DH group element value",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.ec.xlen"] = {
+ name = "Elliptic curve x-coordinate length",
+ type = ftypes.UINT16, base = base.DEC
+ },
+ ["tripe.ec.x"] = {
+ name = "Elliptic curve x-coordinate value",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.ec.ylen"] = {
+ name = "Elliptic curve y-coordinate length",
+ type = ftypes.UINT16, base = base.DEC
+ },
+ ["tripe.ec.y"] = {
+ name = "Elliptic curve y-coordinate value",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.x25519.x"] = {
+ name = "X25519 x-coordinate",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ ["tripe.x448.x"] = {
+ name = "X448 x-coordinate",
+ type = ftypes.BYTES, base = base.SPACE
+ },
+ }
+
+ -- Convert this table into the protocol fields, and populate `PF'.
+ local ff = { }
+ local i = 1
+
+ -- Figure out whether we can use `none' fields (see below).
+ -- probe for this easily
+ local use_none_p = rawget(ProtoField, 'none') ~= nil
+ for abbr, args in pairs(ftab) do
+
+ -- An annoying hack. Older versions of Wireshark don't allow setting
+ -- fields with type `none', which is a shame because they're ideal as
+ -- internal tree nodes.
+ ty = args.type
+ b = args.base
+ if ty == ftypes.NONE and not use_none_p then
+ ty = ftypes.BYTES
+ b = base.SPACE
+ end
+
+ -- Go make the field.
+ local f = ProtoField.new(args.name, abbr, ty,
+ args.tab, b, args.mask, args.descr)
+ PF[abbr] = f
+ ff[i] = f; i = i + 1
+ end
+ tripe.fields = PF
+end
+
+-----------------------------------------------------------------------------
+--- The main dissector.
+
+function tripe.dissector(buf, pinfo, tree)
+
+ -- Fill in the obvious stuff.
+ pinfo.cols.protocol = "TrIPE"
+
+ local sz = buf:reported_length_remaining()
+ local sub = tree:add(tripe, buf(0, sz), "TrIPE packet")
+ local p = 1
+
+ -- Decode the packet type octet.
+ local tycode = buf(0, 1):uint()
+ local ty = sub:add(PF["tripe.type"], buf(0, 1))
+ ty:add(PF["tripe.cat"], buf(0, 1))
+ local cat = bit.rshift(bit.band(tycode, 0xf0), 4)
+ local subty = bit.band(tycode, 0x0f)
+ local info = PKTINFO[cat]
+
+ -- Dispatch using the master protocol table.
+ if info == nil then
+ pinfo.cols.info = string.format("Unknown category code %u, " ..
+ "unknown type code %u",
+ cat, subty)
+ else
+ ty:add(PF[info.subtype], buf(0, 1))
+ local subinfo = info.sub[subty]
+ if subinfo == nil then
+ pinfo.cols.info = string.format("%s, unknown type code %u",
+ info.info, subty)
+ else
+ pinfo.cols.info = string.format("%s, %s", info.info, subinfo.info)
+ p = 1
+ for _, d in ipairs(subinfo.dissect) do p = d(buf, sub, p, sz) end
+ end
+ end
+
+ -- Return the final position we reached.
+ return p
+end
+
+-- We're done. Register the dissector.
+DissectorTable.get("udp.port"):add(4070, tripe)
+
+-------- That's all, folks --------------------------------------------------
~mdw / tripe / commitdiff