Merge pull request #48 from guardian/add-docs-on-rotating-the-pgp-key…

…pair

Add docs on using a new PGP keypair

docs/credentials/generating-credentials.md

@@ -21,16 +21,7 @@ Note these points:
 
 ## Generating a new PGP key
 
-See [Sonatype's instructions](https://central.sonatype.org/publish/requirements/gpg/#generating-a-key-pair) for
-generating a keypair - ensure you upload the public key to a [keyserver](https://keyserver.ubuntu.com/).
-
-However, note that `gha-scala-library-release-workflow` requires a
-[**passphrase-less** private key](https://unix.stackexchange.com/a/550538/46453), and that key
-should be plaintext, not BASE64-encoded.
-
-```shell
-gpg --armor --export-secret-key [insert key fingerprint here] | pbcopy
-```
+See the full docs on [using a new PGP key](pgp-keys.md).
 
 ## Generating a new GitHub App private key
 

docs/credentials/pgp-keys.md

@@ -0,0 +1,66 @@
+# New PGP keys
+
+**Guardian developers:** [further docs here](https://docs.google.com/document/d/1zA8CHa1a8faemorWokUlbkdexYzpilalqcPFwkRu92M/edit?tab=t.0#heading=h.mnrh0k50nysb).
+
+There are 4 steps to performing a credential rotation on the PGP key used by `gha-scala-library-release-workflow`:
+
+## Generate new PGP keypair
+
+The keypair should have a [**passphrase-less** private key](https://unix.stackexchange.com/a/550538/46453) -
+if you're generating the keypair, you can just enter blank passphrases.
+
+```bash
+gpg --quick-generate-key "Example Automated Maven Release <automated.maven@example.com>"
+```
+
+This will give a new key id, eg like `EF53C0E05A7067985C09F1B2AAE7330D94C67345`.
+
+## Publish Public PGP key
+
+Maven Central _requires_ that the public PGP key is published to public keyservers - it will
+[_reject_](https://github.com/guardian/redirect-resolver/actions/runs/12158544330/job/33906914072#step:5:63)
+artifacts that are signed with unknown PGP keys:
+
+> Failed: signature-staging, failureMessage:No public key: Key with id: (aae7330d94c67345) was not able to be located on <a href="http://pgp.mit.edu:11371/">http://pgp.mit.edu:11371/</a>. Upload your public key and try the operation again.
+
+The [official instructions](https://central.sonatype.org/publish/requirements/gpg/#distributing-your-public-key)
+say to use `gpg --keyserver` to publish the key, but unfortunately this gives
+`gpg: keyserver send failed: Network is unreachable` errors - so instead we have to
+manually paste our key into a web form on a PGP keyserver website.
+
+Execute this command to get the new public key copied into your copy-n-paste:
+
+```bash
+gpg --armor --export [insert key fingerprint here] | pbcopy
+```
+
+_N.B. The above command uses `--export`, not `--export-secret-key` - we do **not** want
+to publicly share our private key._
+
+You can use either (or both) of these keyservers:
+
+* https://keyserver.ubuntu.com/#submitKey - this _feels_ kind of more stable, and search works
+* https://pgp.mit.edu/ - Maven Central seems to be checking keys with this keyserver
+
+PGP keyservers are supposed to synchronise with each other, so wherever you publish the
+key it should eventually make it to the keyserver that Maven Central is checking with - but
+for the time being, publishing to `pgp.mit.edu` may get the key available sooner.
+
+## Store Private PGP key in a GitHub secret
+
+Execute this command to get the private key copied into your copy-n-paste:
+
+```
+gpg --armor --export-secret-key [insert key fingerprint here] | pbcopy
+```
+
+This can then be pasted into a GitHub secret.
+
+**Guardian developers:** We use the organisation-level GitHub secret
+[`AUTOMATED_MAVEN_RELEASE_PGP_SECRET`](https://github.com/organizations/guardian/settings/secrets/actions/AUTOMATED_MAVEN_RELEASE_PGP_SECRET) -
+as it's organisation-level, only an owner of our GitHub organisation can access it.
+
+## Destroy or secure your local copy of the PGP key
+
+As the private key had to be made **passphrase-less**, it is now vulnerable, and
+should be deleted or [edited](https://stackoverflow.com/q/77716552/438886) to add a passphrase.