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rocksolid / Security / Re: Removing domains from letsencrypt certs

SubjectAuthor
* Removing domains from letsencrypt certsRetro Guy
`* Re: Removing domains from letsencrypt certsGuest
 `- Re: Removing domains from letsencrypt certsRetro Guy

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Subject: Removing domains from letsencrypt certs
From: Retro Guy
Newsgroups: rocksolid.shared.security
Organization: RetroBBS
Date: Sat, 21 Nov 2020 00:11 UTC
Path: i2pn2.org!rocksolid2!.POSTED.localhost!not-for-mail
From: retro_...@retrobbs.rocksolidbbs.com (Retro Guy)
Newsgroups: rocksolid.shared.security
Subject: Removing domains from letsencrypt certs
Date: Fri, 20 Nov 2020 17:11:52 -0700
Organization: RetroBBS
Message-ID: <20201120171152.29466827@desktop14.dt>
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I wanted to drop this here for future reference. I needed this info and
found this post from
https://community.letsencrypt.org/t/remove-domain-not-required-from-cert/14010/6
very helpful.

Credit to pfg for posting this:

Right now, the procedure for that would probably be something like this:

Before you start, create a backup of /etc/letsencrypt just in case,
i.e. cp /etc/letsencrypt/ /etc/letsencrypt.backup -r

Let’s say you have two certificate lineages, foo.example.com and
bar.example.com. The certificates for foo.example.com are stored
in /etc/letsencrypt/live/foo.example.com, for bar.example.com
in /etc/letsencrypt/live/bar.example.com.

If you’re unsure which lineage contains which domains, try this for all
subdirectories in /etc/letsencrypt/live:

openssl x509 -in /etc/letsencrypt/live/example.com/cert.pem -text
-noout | grep DNS

If you want to remove everything in the bar.example.com lineage (that
is, bar.example.com and any other domains covered by that certificate),
you can delete the following files:

rm -rf /etc/letsencrypt/live/bar.example.com/
rm -rf /etc/letsencrypt/archive/bar.example.com/
rm /etc/letsencrypt/renewal/bar.example.com.conf

That’s it.

If you just want to remove one (or a couple) of domains that were
included in the bar.example.com - let’s say you don’t want
sample.bar.example.com, but still need othersample.bar.example.com and
bar.example.com - you can use the same rm commands, and afterwards
request a new certificate using only the domains you want to keep. Full
example (with webroot, but you can of course use whatever you initially
used to get the certificates):

rm -rf /etc/letsencrypt/live/bar.example.com/
rm -rf /etc/letsencrypt/archive/bar.example.com/
rm /etc/letsencrypt/renewal/bar.example.com.conf
# this will install a new certificate in bar.example.com, excluding
sample.bar.example.com ./letsencrypt-auto certonly --webroot -d
bar.example.com -d othersample.bar.example.com -w /var/www/html/

If anything goes wrong while you’re doing this, run
mv /etc/letsencrypt /etc/letsencrypt.broken &&
mv /etc/letsencrypt.backup/ /etc/letsencrypt and you’re back where you
started. :smile:

Hope this helps!



Subject: Re: Removing domains from letsencrypt certs
From: Guest
Newsgroups: rocksolid.shared.security
Organization: Dancing elephants
Date: Tue, 24 Nov 2020 17:28 UTC
References: 1
Path: i2pn2.org!rocksolid2!def5!.POSTED.bogusentry!not-for-mail
From: gue...@retrobbs.rocksolidbbs.com (Guest)
Newsgroups: rocksolid.shared.security
Subject: Re: Removing domains from letsencrypt certs
Date: Tue, 24 Nov 2020 12:28:21 -0500
Organization: Dancing elephants
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Will that screw up Certificate Pinning (also a Firefox Add-On).  I'm so paranoid that I keep lists of fingerprints, certificates and sha etc...  only for transaction and email.  Once burned twice shy!

--
Posted on def3


Subject: Re: Removing domains from letsencrypt certs
From: Retro Guy
Newsgroups: rocksolid.shared.security
Organization: RetroBBS
Date: Tue, 24 Nov 2020 23:12 UTC
References: 1 2
Path: i2pn2.org!rocksolid2!.POSTED.localhost!not-for-mail
From: retro_...@retrobbs.rocksolidbbs.com (Retro Guy)
Newsgroups: rocksolid.shared.security
Subject: Re: Removing domains from letsencrypt certs
Date: Tue, 24 Nov 2020 16:12:34 -0700
Organization: RetroBBS
Message-ID: <20201124161234.09f33cf1@desktop14.dt>
References: <20201120171152.29466827@desktop14.dt>
<rpjic9$avf$1@def5.org>
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On Tue, 24 Nov 2020 12:28:21 -0500
Guest <guest@retrobbs.rocksolidbbs.com> wrote:

Will that screw up Certificate Pinning (also a Firefox Add-On).  I'm
so paranoid that I keep lists of fingerprints, certificates and sha
etc...  only for transaction and email.  Once burned twice shy!

It should appear to a client most likely the same as if the cert was
revoked then reissued. Depending on your pinning settings, it may or
may not be an issue.

Jeremy Rowley at digicert wrote an interesting article on pinning that
basically agrees with my views:

Stop Certificate Pinning

What is certificate pinning?

Certificate pinning restricts which certificates are considered valid
for a particular website, limiting risk. Instead of allowing any
trusted certificate to be used, operators “pin” the certificate
authority (CA) issuer(s), public keys or even end-entity certificates
of their choice. Clients connecting to that server will treat all other
certificates as invalid and refuse to make an HTTPS connection.

Pinning allows websites to control the risk of misissuance, CA
compromise, or man-in-the-middle attacks. Pinning takes multiple forms
depending on the use case – I can pin my certificate as the only one in
my client trust store or write the public key hash into my code so only
my key is trusted. When pinning started becoming popular, the hope was
that these extra layers of complexity made it harder for bad actors to
use certificates in attacks or spoofs.

Google was one of the first to use pinning in 2011, when they pinned
the issuing CAs for their main websites in the Chrome browser. When
Chrome connected to google.com, it already knew which CAs to accept. If
a certificate from any other CA was presented, the connection would be
blocked. This meant that if an attacker managed to fool any other
trusted CA into giving them a certificate for google.com, it would
still be blocked by Chrome.

A few years later, Chrome and Firefox started allowing sites to use
HTTP Public Key Pinning (HPKP) headers. The first time your browser
connected to a website using HPKP, it recorded the public key from the
header, and would only accept that key every time it connected to the
site, up until the “max-age” defined in the HPKP policy. If a max-age
of 60 days was set, no other keys would be accepted for the next 60
days.

Meanwhile, certificate pinning was also introduced in apps, IoT
devices, and other software. Using similar methods an app could pin a
certificate, and the app would then refuse any connections to the
server if they were not using that certificate, protecting users from
any man-in-the-middle attack.

These practices, when implemented correctly, could enhance security,
but it did not take long for the web community to find out pinning was
not such a great idea.

What can go wrong with Certificate Pinning?

Pinning, especially with HPKP, was extremely risky and error prone. If
you configured your pinning settings incorrectly, you could block
access to your own website or break connectivity in your application,
with limited options for recourse. Here are just a few ways pinning can
cause such harm.

Key Compromise

A common practice with HPKP was to pin the end-entity certificate
public key to a website for 60 days. Many sites did not specify any
backup keys, perhaps because they were unaware it was an option, or
they underestimated the risk of using a single key.

This left sites vulnerable to key compromise. Industry standards
require that CAs revoke compromised certificates – perhaps stolen from
an insecure webserver, or accidentally uploaded to a public GitHub
repository – within 24 hours. With your only pinned key now
compromised, you have no replacement and clients who recorded your HPKP
policy remember that bad key and will not allow connections with your
new certificate.

Hackers

HPKP is a great way for hackers to sabotage a website and do long-term
damage. If I can take over your server and set a bogus HPKP policy for
a fake key and a one-year max-age, browsers will always fail to
connect. Long after you re-secure your server, you are still stuck with
the effects of that HPKP policy that are not easy to fix.

Certificate Authority Revocations

Sometimes CAs must revoke your certificates. Maybe an audit shows the
certificates have previously unknown issues, like misspellings in the
subject name or invalid entries in the OU fields. Industry standards
say the CA has five days to revoke your certificates, but you pinned
them in your client code. How can you push out updates to all your
clients in five days to start using your new replacement certificates?

More risk than reward

As a result of these problems and the difficulties of implementing
pinning safely and robustly, there were more cases of sites being
harmed by pinning than protected. These are just a few of the issues
with pinning which led Google and Firefox to remove HPKP support just a
couple years after it was introduced.

The biggest problem with pinning is that you lose the ability to
respond to certificate issues. If you need to change keys,
certificates, issuers, or your CA vendor, for any reason, you must fix
your client, browser, code, IoT device, etc. – sometimes on a short
schedule. If you are committed to supporting an application version for
years and it contains a pinned certificate, how can you be sure the
certificate will remain valid for the entire lifetime of your
application? Pinning is especially problematic with publicly trusted
TLS certificates because they must adhere to ever-evolving rules,
decreasing maximum lifetimes and other surprises.

Luckily, HPKP is a thing of the past, and DigiCert has not been a big
proponent of other types of public key pinning. DigiCert recommends you
do not use pinning; the complexities and consequences outweigh the
benefits.

What is DigiCert doing to discourage inappropriate pinning?

While we haven’t recommended or instructed users to implement pinning
in recent years, it is still possible to set up pinning on your own.
This week, DigiCert is making a change to our CA hierarchy. We will
start replacing our public TLS-issuing intermediate CAs (ICAs) with
shorter versions, updated every six months. Of course, the validity
periods of the intermediates will be long enough to exceed all the one-
and two-year certificates issued during the six months the ICAs are
used. Shorter ICA lifetimes will disincentivize pinning them since they
will be changing more frequently.

We will initially replace the GeoTrust RSA CA 2018 and RapidSSL RSA CA
2018 intermediates for Domain Validated (DV) issuance with the new
GeoTrust TLS DV RSA Mixed SHA256 2020 CA-1 and RapidSSL TLS DV RSA
Mixed SHA256 2020 CA-1. After six months, these will be replaced by the
GeoTrust TLS DV RSA Mixed SHA256 2021 CA-1 and RapidSSL TLS DV RSA
Mixed SHA256 2021 CA-1, then six months later, the *2021 CA-2 versions,
and so on.

Additional CAs will be replaced over the coming months until all our
default public TLS issuers are are rotated every six months. The
schedule for these replacements will be posted here:

Beyond helping put pinning behind us all, shortening ICA lifetimes will
have other benefits. It will group certificates into smaller buckets so
changes to one set of certificates issued under one CA will not always
affect others. If an ICA must be deprecated, it will only affect the
certificates issued for the six months that CA was actively issuing,
and only the specific types of certificates that were allowed under
that CA.



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