suri-xor-binary-quick.lua

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This lua script can be run standalone and verbosely on a binary file with
echo "run()" | lua -i <script name> <binary file>

Chris Wakelin
--]]

function init (args)
    local needs = {}
    needs["http.response_body"] = tostring(true)
    return needs
end

function xor0(byte, key)
   local bit = require("bit")
   if byte == key or byte == 0 then
       return byte
   end
   return bit.bxor(byte,key)
end

-- return match via table
function common(a,verbose)
    local bit = require("bit")

    key = {}

    if #a < 1024 then 
        return 0
    end

-- Usually bytes 0x30 to 0x3b are 0-padding,
-- so may actually contain the Key; decode PE offset at 0x3c and check
-- it points to bytes that then decode to PE|00 00|
-- 7,8,9,10,11,12 also cover their divisors 1 - 6, but include 4 four safety

    key_lengths = {4,7,8,9,10,11,12}

    for n, l in pairs(key_lengths) do

        koffset = ((l-(0x30 % l)) % l)

        for i = 0, l-1, 1 do
           key[i+1] = a:byte(0x30+1+((i+koffset) % l))
        end
        

        pe = bit.bxor(a:byte(0x3c+1), key[1+(0x3c % l)]) + (256*bit.bxor(a:byte(0x3c+2), key[1+((0x3c+1) % l)]))
        if verbose==1 then print("Trying " .. l .. "-byte XOR key; PE block at " .. pe) end
        if ((pe < 4096) and (pe < #a-4)) then
            offset = pe % l
            if (bit.bxor(a:byte(pe+1), key[offset+1]) == string.byte('P')) and 
               (bit.bxor(a:byte(pe+2), key[((1+offset)%l)+1]) == string.byte('E')) and
               (bit.bxor(a:byte(pe+3), key[((2+offset)%l)+1]) == 0) and
               (bit.bxor(a:byte(pe+4), key[((3+offset)%l)+1]) == 0) then
                if verbose==1 then print("Found " .. l .. "-byte XOR key; PE block at " .. pe) end
                return 1
            end
        end
    end

-- Check for g01pack/Blackhole 1-byte XOR key
    k = a:byte(1);
    pe = bit.bxor(a:byte(0x3c+2), k) + (256*bit.bxor(a:byte(0x3c+3),k))
    if ((pe < 4096) and (pe < #a-5)) then
        if (bit.bxor(a:byte(pe+2), k) == string.byte('P')) and 
           (bit.bxor(a:byte(pe+3), k) == string.byte('E')) and
           (bit.bxor(a:byte(pe+4), k) == 0) and
           (bit.bxor(a:byte(pe+5), k) == 0) then
            if verbose==1 then print("Found g01pack 1-byte XOR key " .. k .. " - PE block at " .. pe) end
            return 1
        end
    end

-- Check for SofosFO-obfuscated binary

    b = ""
    -- Quick check that 2nd byte -> 'Z'
    k1 = bit.bxor(a:byte(1), string.byte('M'))
    k2 = bit.bxor((k1 + 170) % 256, 0x48)

    if (bit.bxor(a:byte(2),k2) == string.byte('Z')) and (#a > 2048) then 
    -- now check for a PE header
        k = (bit.bxor(a:byte(1), string.byte('M'), 0x48) - 170) % 256
        k1 = k
          for i = 1, 2048, 1 do
          k = bit.bxor((k + 170) % 256, 0x48)
          b = b .. string.char(bit.bxor(a:byte(i), k))
        end

        pe = b:byte(0x3c+1) + (256*b:byte(0x3c+2))

        if ((pe < 2048) and (pe < #b-4)) then
            if b:byte(pe+1) == string.byte('P') and
               b:byte(pe+2) == string.byte('E') and
               b:byte(pe+3) == 0 and
               b:byte(pe+4) == 0 then
                if verbose==1 then print("Found SofosFO XOR seed " .. k1 .. " - PE block at " .. pe) end
                return 1
            end
        end
    end

-- Check for Blackhole - long int obfuscated binary
    b = "MZ\144\0" 
    k = a:byte(1) + (a:byte(2)*256) + (a:byte(3)*256*256) + (a:byte(4)*256*256*256)
    k2 = k % 2
    k3 = k % 3
    for i = 5, 2048, 1 do
        c = a:byte(i)
        k = bit.band((k * 0x343fd) + 0x269ec3,0x7fffffff)
        x = (k % 241) + 15
        k = bit.band((k * 0x343fd) + 0x269ec3,0x7fffffff)
        r = (k % 6) + 1
        if k2 == 0 then
            c = bit.bor(bit.lshift(c,r),bit.rshift(c,8-r)) % 256
        else
            c = bit.bor(bit.rshift(c,r),bit.lshift(c,8-r)) % 256
        end
        if k3 == 0 then
            c = bit.bxor(c,x)
        elseif k3 == 1 then
            c = (c - x) % 256
        else
            c = (c + x) % 256
        end
        -- Quick check that byte 5 -> 0x03
        if i == 5 and c ~= 3 then break end
        b = b .. string.char(c)
    end
    if #b == 2048 then
        pe = b:byte(0x3c+1) + (256*b:byte(0x3c+2))

        if ((pe < 2048) and (pe < #b-4)) then
            if b:byte(pe+1) == string.byte('P') and
               b:byte(pe+2) == string.byte('E') and
               b:byte(pe+3) == 0 and
               b:byte(pe+4) == 0 then
                if verbose==1 then print("Found Blackhole long int encoding - PE block at " .. pe) end
                return 1
            end
        end
    end

-- Check for Fiesta - 256-byte seeded XOR
    n = 0
    m = 0
    b = ""
    k = a:sub(1,256); -- key string
    for i = 1, 2048, 1 do
        n = (n + 1) % 256
        m = (m + k:byte(n+1)) % 256
        -- swap char n and m in the key string
        if n < m then
           k = k:sub(1,n) .. k:sub(m+1,m+1) .. k:sub(n+2,m) .. k:sub(n+1,n+1) .. k:sub(m+2)
        elseif n > m then
           k = k:sub(1,m) .. k:sub(n+1,n+1) .. k:sub(m+2,n) .. k:sub(m+1,m+1) .. k:sub(n+2)
        end
        c = bit.bxor(a:byte(i+256),k:byte(((k:byte(n+1)+k:byte(m+1)) % 256) + 1))
        -- Quick check that first two bytes are "MZ"
        if i == 1 and c ~= string.byte('M') then break end
        if i == 2 and c ~= string.byte('Z') then break end
        b = b .. string.char(c)
    end
    if #b == 2048 then
        pe = b:byte(0x3c+1) + (256*b:byte(0x3c+2))

        if ((pe < 2048) and (pe < #b-4)) then
            if b:byte(pe+1) == string.byte('P') and
               b:byte(pe+2) == string.byte('E') and
               b:byte(pe+3) == 0 and
               b:byte(pe+4) == 0 then
                if verbose==1 then print("Found Fiesta encryption - PE block at " .. pe) end
                return 1
            end
        end
    end
       
-- Check for XOR with 0 and XOR-key bytes left alone
-- PE offset is (nearly?) always divisible by 8, so key lengths 1,2,4 will always be detected
-- Can match other key lengths in some cases where the remainder on dividing into 0x3c is 0,1,2 or 4
-- and on dividing into the PE offset is 0 or 1 (or 4 when the key length is 5)
    key = {xor0(a:byte(1), string.byte('M')), xor0(a:byte(2), string.byte('Z')), xor0(a:byte(3), 0x90), 0, xor0(a:byte(5), 0x03), 0, 0, 0}

    key_lengths = {1,3,5,6,7,8}
    for n,l in pairs(key_lengths) do
      
        koffset = 0x3c % l
        pe = xor0(a:byte(0x3c+1),key[1+koffset]) + (256*xor0(a:byte(0x3c+2),key[((1+koffset) % l) + 1]))
        if verbose==1 then print("Trying PE header at " .. pe) end

        koffset = pe % l
        if ((pe < 4096) and (pe < #a-4)) then
            if xor0(a:byte(pe+1),key[1+koffset]) == string.byte('P') and
               xor0(a:byte(pe+2),key[((1+koffset) % l) + 1]) == string.byte('E') and
               a:byte(pe+3) == 0 and
               a:byte(pe+4) == 0 then
                if verbose==1 then print("Found " .. l .. "-byte XOR-but-not-zero key " .. key[1] .. "," .. key[2] .. " - PE block at " .. pe) end
                return 1
            end
        end
    end

-- Check for NicePack reversed/4-byte XORed binary
    for i = 0, 4, 1 do
      key[i+1] = a:byte(#a-0x30-i)
    end

    pe = bit.bxor(a:byte(#a-0x3c), key[1]) + (256*bit.bxor(a:byte(#a-0x3c-1), key[2]))
    if ((pe < 4096) and (pe < #a-4)) then
        offset = pe % 4
        if (bit.bxor(a:byte(#a-pe), key[offset+1]) == string.byte('P')) and 
           (bit.bxor(a:byte(#a-1-pe), key[((1+offset)%4)+1]) == string.byte('E')) and
           (bit.bxor(a:byte(#a-2-pe), key[((2+offset)%4)+1]) == 0) and
           (bit.bxor(a:byte(#a-3-pe), key[((3+offset)%4)+1]) == 0) then
            if verbose==1 then print("Found 4-byte XOR key for reversed binary; PE block at " .. pe) end
            return 1
        end
    end

-- Check for Magnitude subtract single byte - 4th byte is usually "0"
    k = a:byte(4);
    pe = ((a:byte(0x3c+1) - k) % 256) + (256*((a:byte(0x3c+2)-k) % 256))
    if ((pe < 4096) and (pe < #a-5)) then
        if ((a:byte(pe+1) - k) % 256 == string.byte('P')) and 
           ((a:byte(pe+2) - k) % 256 == string.byte('E')) and
           ((a:byte(pe+3) - k) % 256 == 0) and
           ((a:byte(pe+4) - k) % 256 == 0) then
            if verbose==1 then print("Found Magnitude 1-byte subtract key " .. k .. " - PE block at " .. pe) end
            return 1
        end
    end

-- Check for Upatre LZNT1-compressed + 4-byte incrementing XORed binary

    key[1] = bit.bxor(a:byte(9),string.byte('Z'))
    key[2] = bit.bxor(a:byte(10),0x90)
    key[3] = a:byte(7)
    key[4] = bit.bxor(a:byte(8),string.byte('M'))
    k = key[1]+(256*key[2])+(256*256*key[3])+(256*256*256*key[4])
    if k > 0 then
        b = ""
        for i = 9,20,4 do
          k1 = bit.bxor(k,a:byte(i)+(256*a:byte(i+1))+(256*256*a:byte(i+2))+(256*256*256*a:byte(i+3)))
          b = b .. string.char(k1 % 256) .. string.char(bit.rshift(k1,8) % 256) .. string.char(bit.rshift(k1,16) % 256) .. string.char(bit.rshift(k1,24) % 256)
          k = k+1
        end
        if b == "Z\144\0\003\0\0\0\130\004\0\048\255" then
            if verbose==1 then print("Found Upatre 4-byte XOR key for LZNT1-compressed binary") end
            return 1
        end
    end


    return 0
end


-- return match via table
function match(args)
    local t = tostring(args["http.response_body"])
    return common(t,0)
end

function run()
  local f = io.open(arg[1])
  local t = f:read("*all")
  f:close()
  common(t,1)
end