[tor-dev] SSL Observatory Observations

[Tim Wilde <twilde@xxxxxxxxx>]

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G'morning all!

Last weekend's hackfest inspired me to attempt to run some numbers on
the EFF SSL Observatory data[1], in particular looking at two things:
the commonality of the "Internet Widgits Pty" organization string (a
default in OpenSSL's CSR generator) in self-signed certificate subjects,
and, further to that, the most commonly seen self-signed certificates in
the data.

Using the CSV data from the observatory, I found that out of 5,618,558
total certs in the all-certs file, only 8,891 contained subjects that
matched the regex /Internet Widg[ie]ts Pty/ (a quick search observed
both spellings; my OpenSSL used Widgits, FWIW.  I further recorded the
subjects of all certs where subject == issuer, and counted each, with
the following results for the top 10:

' C=--, ST=SomeState, L=SomeCity, O=SomeOrganization,
OU=SomeOrganizationalUnit,
CN=localhost.localdomain/emailAddress=root@xxxxxxxxxxxxxxxxxxxxx': 154867
' C=US, ST=California, L=Sunnyvale, O=HTTPS Management Certificate for
SonicWALL (self-signed), OU=HTTPS Management Certificate for SonicWALL
(self-signed), CN=192.168.168.168': 111453
' C=US, ST=Virginia, L=Herndon, O=Parallels, OU=Plesk,
CN=plesk/emailAddress=info@xxxxxxxxx': 82689
' CN=Fortinet, O=Fortinet Ltd.': 54975
' C=US, ST=Virginia, L=Herndon, O=SWsoft, Inc., OU=Plesk,
CN=plesk/emailAddress=info@xxxxxxxxx': 53184
' C=USA, ST=California, L=Sunnyvale, O=HTTPS Management Certificate for
SonicWALL (self-signed), OU=HTTPS Management Certificate for SonicWALL
(self-signed), CN=192.168.168.168': 22987
' CN=SpeedTouch 605, O=THOMSON, OU=DSL Internet Gateway Device': 16790
' C=US, ST=Someprovince, L=Sometown, O=none, OU=none,
CN=localhost/emailAddress=webaster@localhost': 16638
' CN=SpeedTouch 5x6, O=THOMSON, OU=DSL Internet Gateway Device': 15286
' C=US, ST=CA, L=Sunnyvale, O=SonicWALL, Inc., OU=SSL-VPN,
CN=192.168.200.1': 11760

(Apologies for the lousy wrapping; initial spaces are present in the
source data.)  The numbers after the colons are, as you may guess, the
total number of self-signed certificates with that subject.

It may be instructive to dig into the netblocks where these subjects
occur and attempt to determine the context in which they occur.  For the
purposes of making Tor appear unblockable due to collateral damage, my
strong suspicion is that these will not be all that helpful, as they are
quite likely (and in some cases, clearly) used by CPE devices and the
like for internal management, and thus won't really be likely to cause
much difficulty for the censors if blocked.

My personal thinking is that the methodology in Jake's TLS normalization
proposal[2] makes a lot of sense.  Perhaps one modification, per the
discussion at the hackfest, would be to stick to making the server's
presented certificates self-signed, as that is probably more normal than
having random unknown issuers, and less provably false than faking a
known issuer like GoDaddy.

Even ignoring the question of whether or not a censor may be willing to
sustain the collateral damage of blocking one of the common self-signed
subjects above, by using a commonName that varies per bridge/relay and
other certificate fields that also vary widely (and in fact may be
randomized to some extent), we don't present any blockable static values
in our certificate subject or issuer and can focus on other fun stuff in
the certs. :)

Hopefully Jake hasn't already made this all a moot point while I was in
the other room working with Andrew on Saturday and I just haven't heard
about it yet. :)  Further thoughts/discussions/flames welcome (but only
if the flames come from Mike).

Regards,
Tim

[1] https://www.eff.org/observatory
[2]
https://gitweb.torproject.org/tor.git/blob/HEAD:/doc/spec/proposals/ideas/xxx-draft-spec-for-TLS-normalization.txt

- -- 
Tim Wilde, Senior Software Engineer, Team Cymru, Inc.
twilde@xxxxxxxxx | +1-630-230-5433 | http://www.team-cymru.org/
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