Network traffic monitoring: BSD monitor & verifying encryption

Matthew Seaman m.seaman at
Wed Jul 8 18:09:14 UTC 2009

Daniel Underwood wrote:
> Thanks for the help.
> I couldn't find any flags/fields in TCP packets indicated whether
> encrypted (as in the case of SSH packets).  There isn't any, right?

Correct: there isn't anything like that in the TCP headers.  Encryption
on TCP streams is an application level thing that only affects packet

There are transport layer encryption protocols -- eg. IPSec, OpenVPN, etc.
-- but those allow tunnelling TCP streams through them and aren't necessarily
TCP themselves.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP:     Ramsgate
                                                  Kent, CT11 9PW

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