$ man journalctl ... --setup-keys Instead of showing journal contents, generate a new key pair for Forward Secure Sealing (FSS). This will generate a sealing key and a verification key. The sealing key is stored in the journal data directory and shall remain on the host. The verification key should be stored externally. Refer to the Seal= option in journald.conf(5) for information on Forward Secure Sealing and for a link to a refereed scholarly paper detailing the cryptographic theory it is based on. ... --verify Check the journal file for internal consistency. If the file has been generated with FSS enabled and the FSS verification key has been specified with --verify-key=, authenticity of the journal file is verified. --verify-key= Specifies the FSS verification key to use for the --verify operation.
afaik, signing in a PKI system works only If we have the private key.
afaik the advise: "The verification key should be stored externally." is that the private key (?) should be stored at another place?
Q: So how are the encrypted log messages signed in this situation?
afaik if the encrypted logs aren't signed, then an attacker can fake the logs, by encrypting the modified ones, and it will be accepted, since they are not signed. But keeping the private key there too is again bad, since they could be signed by the attacker.