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Hi,

one year ago [0] we tried to convince you to add support for a new
socket option to the linux kernel. Equipped with an improved version of
our patch we're back to accomplish this task today. :-)

TCP Stealth is a modern variant of port knocking which borrows
techniques from network steganography to enable clients to authenticate
themselves towards a server on TCP level. You can find technical details
in an rfc draft we wrote earlier this year [1] and in my master's thesis
[2]. In summary, TCP Stealth derives authentication information from a
pre-shared secret and embeds it into the ISN sent along with the first
SYN from the client.

Our motivation is simple: During this year we gained hard evidence on
secret services actively port scanning the internets followed by
exploitation of your services using 0-day exploits [3, 4]. We don't want
our machines to be turned into relays from where they continue to
cascade their attacks. TCP Stealth makes port scanning more expensive by
a factor of 2^31 (on average).

A copy of this patch as well as patches for several user space
applications can be found on the project's home page [5].

All the best for the upcoming year,
Julian & Christian



[0] https://lkml.org/lkml/2013/12/10/1155
[1] https://datatracker.ietf.org/doc/draft-kirsch-ietf-tcp-stealth/
[2] https://gnunet.org/kirsch2014knock
[3]
http://www.heise.de/ct/artikel/NSA-GCHQ-The-HACIENDA-Program-for-Internet-Colonization-2292681.html
[4]
https://firstlook.org/theintercept/2014/12/13/belgacom-hack-gchq-inside-story/
[5] https://gnunet.org/knock
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