JKS: Extending a Self-Signed Certificate

by | May 19, 2019 | Aggregated, Developer tips, jks, keytool

Sometimes you don’t have a PKI in place but you still need a key and a corresponding certificate to sign stuff (outside of the TLS context). And after the certificate in initially generated jks file expires, you have few options – either generate an entirely new keypair, or somehow “extend” the existing certificate. This is useful mostly for testing and internal systems, but still worth mentioning. Extending certificates is generally not possible – once they expire, they’re done. However, you can have a new certificate with the same private key and a longer period. This sounds like something that should be easy to do, but it turns it it isn’t that easy with keytool. Even with my favourite tool, keystore explorer, it’s not immediately possible. In order to reuse the private key to have a new, longer certificate, you need to do the following: Export the private key (with keytool & openssl or through the keystore-explorer UI, which is much simpler) Make a certificate signing request (with keytool or through the keystore-explorer UI) Sign the request with the private key (i.e. self-signed) Import the certificate in the store to replace the old (expired) one The last two steps seem to be not straightforward with keytool or keystore exporer. If you try to sign the request with your existing keystore keypair, the current certificate is used as the root of the chain (and you don’t want that). And you can’t remove the certificate and generate a new one. So you need to use OpenSSL: x509 -req -days 3650 -in req.csr -signkey private.key -sha256 -extfile extfile.cnf -out result.crt The extfile.cnf is...