Re: NMAP NSE script for iSCSI enumeration

[Patrick Donnelly <batrick () batbytes com>]

On Sat, Oct 10, 2009 at 7:48 PM, Fyodor <fyodor () insecure org> wrote:
> 2) I'm not sure that this approach of table.insert followed by a
>   .concat into a string is an efficient or desirable way to fill out
>   the request payload.  You might have gotten this approach from
>   sslv2.nse, but that is an ancient script and I'm not sure that it
>   serves as a good example in this respect.  Perhaps the approach
>   shown in this dns-random-srcport.nse snippet is better:
>
>   local query =   string.char(0xbe, 0xef, -- TXID
>                               0x01, 0x00, -- Flags
>                               0x00, 0x01, -- Questions
>                               0x00, 0x00, -- Answer RRs
>                               0x00, 0x00, -- Authority RRs
>                               0x00, 0x00, -- Additional RRs
>                               0x08) .. "porttest" ..
>                   string.char(0x08) .. "dns-oarc" ..
>                   string.char(0x03) .. "net" ..
>                   string.char(0x00, -- Name terminator
>                               0x00, 0x10, -- Type (TXT)
>                               0x00, 0x01) -- Class (IN)
>
> Another option is bin.pack (http://nmap.org/nsedoc/lib/bin.html).

table.insert is generally used when the number of concatenations
cannot be known or is unwieldy. The above use of explicit
concatenations of each result from string.char is the most efficient
(table.concat is always less efficient than explicit concatenation).
However, Michael's code could use one single string.char to achieve
the same result:

        hs1 = string.char(0x43, 0x87, 0x00, 0x00, 0x00, 0x00, 0x00,
0xf7, -- comment
                          0x00, 0x02, 0x3d, 0x00, 0x00, 0x00, 0x00,
0x00, -- comment2
                          --[[ ... ]]
                         );

This is all over optimizing what is very simple code but setting a
good example for others to follow is important too.

As Fyodor suggested, bin.pack will probably produce the neatest looking code.

-- 
-Patrick Donnelly

"Let all men know thee, but no man know thee thoroughly: Men freely
ford that see the shallows."

- Benjamin Franklin

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