When using the ACME DNS-01 challenge, there is a possibility of a
failure to resolve the challenge if the record is not propagated
fast enough. To circumvent this generic DNS problem, this adds
a setting to explicitly tell the ACME provider to use a certain DNS
resolver to lookup the challenge.
Signed-off-by: Jeroen Simonetti <jeroen@simonetti.nl>
This should hopefully solve races with DNS servers (such as unbound)
during the activation of a new generation. Previously unbound could
still be unavailable and thus the acme script would fail.
Attempting to reuse keys on a basis different to the cert (AKA,
storing the key in a directory with a hashed name different to
the cert it is associated with) was ineffective since when
"lego run" is used it will ALWAYS generate a new key. This causes
issues when you revert changes since your "reused" key will not
be the one associated with the old cert. As such, I tore out the
whole keyDir implementation.
As for the race condition, checking the mtime of the cert file
was not sufficient to detect changes. In testing, selfsigned
and full certs could be generated/installed within 1 second of
each other. cmp is now used instead.
Also, I removed the nginx/httpd reload waiters in favour of
simple retry logic for the curl-based tests
- Use an acme user and group, allow group override only
- Use hashes to determine when certs actually need to regenerate
- Avoid running lego more than necessary
- Harden permissions
- Support "systemctl clean" for cert regeneration
- Support reuse of keys between some configuration changes
- Permissions fix services solves for previously root owned certs
- Add a note about multiple account creation and emails
- Migrate extraDomains to a list
- Deprecate user option
- Use minica for self-signed certs
- Rewrite all tests
I thought of a few more cases where things may go wrong,
and added tests to cover them. In particular, the web server
reload services were depending on the target - which stays alive,
meaning that the renewal timer wouldn't be triggering a reload
and old certs would stay on the web servers.
I encountered some problems ensuring that the reload took place
without accidently triggering it as part of the test. The sync
commands I added ended up being essential and I'm not sure why,
it seems like either node.succeed ends too early or there's an
oddity of the vm's filesystem I'm not aware of.
- Fix duplicate systemd rules on reload services
Since useACMEHost is not unique to every vhost, if one cert
was reused many times it would create duplicate entries in
${server}-config-reload.service for wants, before and
ConditionPathExists
This reverts commit 5532065d06.
As far as I can tell setting RemainAfterExit=true here completely breaks
certificate renewal, which is really bad!
the sytemd timer will activate the service unit every OnCalendar=,
however with RemainAfterExit=true the service is already active! So the
timer doesn't rerun the service!
The commit also broke the actual tests, (As it broke activation too)
but this was fixed later in https://github.com/NixOS/nixpkgs/pull/76052
I wrongly assumed that PR fixed renewal too, which it didn't!
testing renewals is hard, as we need to sleep in tests.
This allows to have multiple certificates with the same common name.
Lego uses in its internal directory the common name to name the certificate.
fixes#84409
Previously, the NixOS ACME module defaulted to using P-384 for
TLS certificates. I believe that this is a mistake, and that we
should use P-256 instead, despite it being theoretically
cryptographically weaker.
The security margin of a 256-bit elliptic curve cipher is substantial;
beyond a certain level, more bits in the key serve more to slow things
down than add meaningful protection. It's much more likely that ECDSA
will be broken entirely, or some fatal flaw will be found in the NIST
curves that makes them all insecure, than that the security margin
will be reduced enough to put P-256 at risk but not P-384. It's also
inconsistent to target a curve with a 192-bit security margin when our
recommended nginx TLS configuration allows 128-bit AES. [This Stack
Exchange answer][pornin] by cryptographer Thomas Pornin conveys the
general attitude among experts:
> Use P-256 to minimize trouble. If you feel that your manhood is
> threatened by using a 256-bit curve where a 384-bit curve is
> available, then use P-384: it will increases your computational and
> network costs (a factor of about 3 for CPU, a few extra dozen bytes
> on the network) but this is likely to be negligible in practice (in a
> SSL-powered Web server, the heavy cost is in "Web", not "SSL").
[pornin]: https://security.stackexchange.com/a/78624
While the NIST curves have many flaws (see [SafeCurves][safecurves]),
P-256 and P-384 are no different in this respect; SafeCurves gives
them the same rating. The only NIST curve Bernstein [thinks better of,
P-521][bernstein] (see "Other standard primes"), isn't usable for Web
PKI (it's [not supported by BoringSSL by default][boringssl] and hence
[doesn't work in Chromium/Chrome][chromium], and Let's Encrypt [don't
support it either][letsencrypt]).
[safecurves]: https://safecurves.cr.yp.to/
[bernstein]: https://blog.cr.yp.to/20140323-ecdsa.html
[boringssl]: https://boringssl.googlesource.com/boringssl/+/e9fc3e547e557492316932b62881c3386973ceb2
[chromium]: https://bugs.chromium.org/p/chromium/issues/detail?id=478225
[letsencrypt]: https://letsencrypt.org/docs/integration-guide/#supported-key-algorithms
So there's no real benefit to using P-384; what's the cost? In the
Stack Exchange answer I linked, Pornin estimates a factor of 3×
CPU usage, which wouldn't be so bad; unfortunately, this is wildly
optimistic in practice, as P-256 is much more common and therefore
much better optimized. [This GitHub comment][openssl] measures the
performance differential for raw Diffie-Hellman operations with OpenSSL
1.1.1 at a whopping 14× (even P-521 fares better!); [Caddy disables
P-384 by default][caddy] due to Go's [lack of accelerated assembly
implementations][crypto/elliptic] for it, and the difference there seems
even more extreme: [this golang-nuts post][golang-nuts] measures the key
generation performance differential at 275×. It's unlikely to be the
bottleneck for anyone, but I still feel kind of bad for anyone having
lego generate hundreds of certificates and sign challenges with them
with performance like that...
[openssl]: https://github.com/mozilla/server-side-tls/issues/190#issuecomment-421831599
[caddy]: 2cab475ba5/modules/caddytls/values.go (L113-L124)
[crypto/elliptic]: 2910c5b4a0/src/crypto/elliptic
[golang-nuts]: https://groups.google.com/forum/#!topic/golang-nuts/nlnJkBMMyzk
In conclusion, there's no real reason to use P-384 in general: if you
don't care about Web PKI compatibility and want to use a nicer curve,
then Ed25519 or P-521 are better options; if you're a NIST-fearing
paranoiac, you should use good old RSA; but if you're a normal person
running a web server, then you're best served by just using P-256. Right
now, NixOS makes an arbitrary decision between two equally-mediocre
curves that just so happens to slow down ECDH key agreement for every
TLS connection by over an order of magnitude; this commit fixes that.
Unfortunately, it seems like existing P-384 certificates won't get
migrated automatically on renewal without manual intervention, but
that's a more general problem with the existing ACME module (see #81634;
I know @yegortimoshenko is working on this). To migrate your
certificates manually, run:
$ sudo find /var/lib/acme/.lego/certificates -type f -delete
$ sudo find /var/lib/acme -name '*.pem' -delete
$ sudo systemctl restart 'acme-*.service' nginx.service
(No warranty. If it breaks, you get to keep both pieces. But it worked
for me.)
The current weekly setting causes every NixOS server to try to renew
its certificate at midnight on the dot on Monday. This contributes to
the general problem of periodic load spikes for Let's Encrypt; NixOS
is probably not a major contributor to that problem, but we can lead by
example by picking good defaults here.
The values here were chosen after consulting with @yuriks, an SRE at
Let's Encrypt:
* Randomize the time certificates are renewed within a 24 hour period.
* Check for renewal every 24 hours, to ensure the certificate is always
renewed before an expiry notice is sent out.
* Increase the AccuracySec (thus lowering the accuracy(!)), so that
systemd can coalesce the renewal with other timers being run.
(You might be worried that this would defeat the purpose of the time
skewing, but systemd is documented as avoiding this by picking a
random time.)
lego already bundles the chain with the certificate,[1] so the current
code, designed for simp_le, was resulting in duplicate certificate
chains, manifesting as "Chain issues: Incorrect order, Extra certs" on
the Qualys SSL Server Test.
cert.pem stays around as a symlink for backwards compatibility.
[1] 5cdc0002e9/acme/api/certificate.go (L40-L44)
Lego allows users to use the DNS-01 challenge to validate their
certificates. It is mostly backwards compatible, with a few
caveats.
- extraDomains can no longer have different webroots to the
main webroot for the cert.
- An email address is now mandatory for account creation
The following other changes were required:
- Deprecate security.acme.certs.<name>.plugins, as this was
specific to simp-le
- Rename security.acme.validMin to validMinDays, to avoid
confusion and errors. Lego requires the TTL to be specified in
days
- Add options to cover DNS challenge (dnsProvider,
credentialsFile, dnsPropagationCheck)
- A shared state directory is now used (/var/lib/acme/.lego)
to avoid account creation rate limits and share credentials
between certs
In 5532065d06, acme was changed to be
RemainAfterExit=true, but `postRun` commands are implemented as
`ExecStopPost`. Systemd now considers the service to be still running
after simp_le is finished, so won't run these commands (e.g. to reload
certificates in a webserver). Change `postRun` to use `ExecStartPost` to
ensure the commands are run in a timely manner.
A centralized list for these renames is not good because:
- It breaks disabledModules for modules that have a rename defined
- Adding/removing renames for a module means having to find them in the
central file
- Merge conflicts due to multiple people editing the central file
Add a new option permitting to point certbot to an ACME Directory
Resource URI other than Let's Encrypt production/staging one.
In the meantime, we are deprecating the now useless Let's Encrypt
production flag.
Previously setting `allowKeysForGroup = true; group = "foo"` would not
apply the group permission change of the certificates until the service
gets restarted. This commit fixes this by making systemd restart the
service every time it changes.
Note that applying this commit to a system with an already running acme
systemd service doesn't fix this immediately and you still need to wait
for the next refresh (or call `systemctl restart acme-<domain>`). Once
everybody's service has restarted once this should be a problem of the
past.
