XOR using lua

hzrat_handshake.lua describes the lua script to do a bytewise xor operation on the payload of a suricata packet.

local bit = require("bit")

function init(args)
    local needs = {}
    needs["payload"] = tostring(true)
    return needs

function match(args)
    local a = tostring(args["payload"])

    v1 = bit.bxor(a:byte(1), a:byte(3))
    v2 = bit.bxor(a:byte(2), a:byte(4))

    -- SCLogNotice(string.format("%x",v2))
    if v1 == 0x69 and v2 == 0xa4 then
        return 1
    return 0

return 0

The following suricata rule will take usage of the lua script above:

alert tcp any any -> any any (msg:"HZRat handshake detected"; luajit:hzrat_handshake.lua; dsize: 4; classtype:trojan-activity; sid:1009999; rev:1;)

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