sks-keyservers gone. What to use instead?

Question

https://sks-keyservers.net/ says

This service is deprecated. This means it is no longer maintained, and new HKPS certificates will not be issued. Service reliability should not be expected.

Update 2021-06-21: Due to even more GDPR takedown requests, the DNS records for the pool will no longer be provided at all.

Which keyservers can I use for gpg --keyserver "$keyserver1" --recv-key keyid that I can expect not will go away anytime soon?

Solution 1

I chose to use

• pgp.surf.nl
• keyserver.bazon.ru
• agora.cenditel.gob.ve
• pgp.benny-baumann.de

Solution 2

Which keyservers can I use for gpg --keyserver "$keyserver1" --recv-key keyid that I can expect not will go away anytime soon?

The recommendation is to use keys.openpgp.org, however this keyserver only includes User IDs for keys whose owners have personally confirmed via email (basically eliminating large swaths of of the PGP ecosystem). It also does not include any 3rd party signatures on keys to mitigate the possibility of a "poisoned key" attack. As of December 2021, this is the default (if none is configured by the user) keyserver for GnuPG packaged by Debian since gnupg2 2.2.17-1 (released in 2019).

Personally, I'd recommend a Hockeypuck-based keyserver like keyserver.ubuntu.com, which isn't so limited (although it does strip 3rd party signatures). GnuPG has since changed this to the default as of versions 2.2.29 and 2.3.2.

Solution 3

keys.gnupg.net is also gone.

At least keyserver.ubuntu.com is still functional. I was able to use it from GnuPG only after adding a hkps:// prefix and a :443 suffix:

gpg2 --keyserver hkps://keyserver.ubuntu.com:443 --recv-keys XXXXXXXXXXXXXXXX

Notice that its web front-end and many others like https://pgp.key-server.io/ don't let you search for a key by its ID if you enter it like XXXXXXXXXXXXXXXX or XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX, but searching for 0xXXXXXXXXXXXXXXXX or 0xXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX works fine. It also works on https://pgp.mit.edu/, but the lookup is very slow there, and I couldn't get it working via GnuPG.

Solution 4

Alternate public PGP key servers that support access via HKP (like SKS keyservers used to):

• keys.openpgp.org (based on hagrid)
• keyserver.ubuntu.com (based on Hockeypuck)
• keys.mailvelope.com (based on Mailvelope)

Access via other protocols that are supported by GnuPG:

• LDAP: keyserver.pgp.com (based on Broadcom PGP Universal Server)

Due to the fact that the SKS key servers were taken down due to GDPR relevant problems, we should be prepared that, on the long run, only verifying key servers remain available. Verifying key servers demand that the user verifies their email address before the PGP key is published.

(Parts of the information collected from PGP Key Retrieval)

Solution 5

SUMMARY

The Old

To add a little more detail to what nit2savvy has written:

Basically, PGP Keyservers were running on SKS-Keyserver code written decades ago and unmaintained. They got hacked in June 2019 and got taken down permanently. For details, see this post by the maintainer of the GnuPG FAQ Robert J. Hansen SKS Keyserver Network Under Attack.

The New

Several new PGP Keyservers have been written since which implement the HKP Protocol

• Hagrid
• Mailvelope
• Hockeypuck

Verifying keyservers are new servers which verify the email addresses of uploaded keys, and are designed to be ”resistant to the abuse and privacy issues that plague old SKS Keyservers”.

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I would suggest using verifying keyservers:

• keys.openpgp.org based on hagrid and verifying
• keys.mailvelope.com based on Mailvelope and verifying

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The Ubuntu keyserver below does not verify your keys email address but is a new maintained keyserver which may implement verification in the future.

• keyserver.ubuntu.com based on Hockeypuck - does not verify your email address

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Comments

[fuzzydrawrings]

Your question acknowledged that SKS is deprecated and all keyservers using it will eventually be unreliable... what makes you think the SKS-based keyservers you listed will remain reliable?

[Anthony Geoghegan]

Upvoted. I'd point out that when configuring a HKPS keyserver, you can either specify the hkps:// schema or the :443 port number: either will suffice to use HKP over TLS. An advantage of HKPS is that it provides greater privacy and if the user is behind a corporate firewall, port 11371 could be blocked while 443 is unlikely to be.

[Anthony Geoghegan]

I've upvoted your answer as being nice and succinct. There's lots of good documentation about keys.opengp.org and Hagrid but I haven't really researched Hockeypuck yet.

[Admin]

It would be great that people stop spread servers that aren't compliant with the EU GDPR.