Valid, unverified/verified signatures

[Lars Noodén]

On 10/16/26 20:03, Lars Noodén wrote:
> I have a question about the verification of signatures made by SSH keys. 
>   I've pored over the manual page for ssh-keygen(1) but not seen (or 
> have missed) the relevant information.  The search engines have not 
> turned up anything about that use-case either.
> 
> The context is that when using SSH keys to sign files using ssh- 
> keygen(1) there seems to be a flag which shows if a signature is 
> verified or unverified.  Viewing a verification while using increased 
> verbosity shows a unverified status for the key being used:
> 
>   "debug1: Valid (unverified) signature from key SHA256:..."
> 
> I presume that a corresponding verified status is possible.  What should 
> I be looking at to make the signature verified?
> 
> /Lars

FWIW, this is how I get that debugging notice:

# create a file to be signed
$ date > datafile

# create a signing key
$ ssh-keygen -f signer -C 'a key for signing'

# create an allowed signers file
$ sed -e 's/^/namespaces="ProjectA at example.org" /' \
         -e 's/^/*@example.org /' signer.pub \
         >> allowed_signers

# sign the file
$ ssh-keygen -Y sign -f signer -n 'ProjectA at example.org' datafile

# verify the signed file
$ ssh-keygen -Y verify  \
         -n 'ProjectA at example.org' \
         -s datafile.sig \
         -f allowed_signers \
         -I lars at example.org \
         -i signer \
         < datafile
Good "ProjectA at example.org" signature for fred at example.org with ED25519 
key SHA256:03u96bPG5qYi7hIEohNDfxOW+KOpMS9LPi4YdiCtGaI

# increased verbosity works, too, but shows a debug warning
$ ssh-keygen -v -Y verify -n 'ProjectA at example.org' \
         -s datafile.sig -f allowed_signers -I lars at example.org \
         -i signer < datafile
debug1: sshsig_verify_fd: signature made with hash "sha512"
debug1: sshsig_wrap_verify: verify message length 64
debug1: Valid (unverified) signature from key 
SHA256:03u96bPG5qYi7hIEohNDfxOW+KOpMS9LPi4YdiCtGaI
debug1: parse_principals_key_and_options: allowed_signers:1: matched 
principal "lars at example.org"
debug1: allowed_signers:1: matched key
Good "ProjectA at example.org" signature for lars at example.org with ED25519 
key SHA256:03u96bPG5qYi7hIEohNDfxOW+KOpMS9LPi4YdiCtGaI

As shown the verification is good, but there is a debug warning about 
the signature being unverified.  Where should I read more about the 
verification process?

/Lars