How to make auto trust gpg public key?

Question

I am trying to add my GPG public key as a part of our appliance installation process. The purpose of it to encrypt any important files like logs before admin pulling them into his local using admin portal and then decrypt them using private key. The plan is to export public key into a file and make appliance installation process to import it using gpg --import command. But I realized, the key is needed to be trusted/signed before do any encryption. How to make this key is trusted without any human intervention at the time of installation? Btw, our appliance os is ubuntu vm and we use kickstart to automate.

Advance thanks for all help.

Answer 1

Your question is really "How do I encrypt to a key without gpg balking at the fact that the key is untrusted?"

One answer is you could sign the key.

gpg --edit-key YOUR_RECIPIENT
sign
yes
save

The other is you could tell gpg to go ahead and trust.

gpg --encrypt --recipient YOUR_RECIPIENT --trust-model always YOUR_FILE

Answer 2

Coincidentally I have a similar situation to the OP - I'm trying to use public/private keys to sign and encrypt firmware for different embedded devices. Since no answer yet shows how to add trust to a key you already have imported, here is my answer.

After creating and testing the keys on a test machine, I exported them as ascii:

$ gpg --export -a <hex_key_id> > public_key.asc
$ gpg --export-secret-keys -a <hex_key_id> > private_key.asc

Then secure-copied and imported them to the build server:

$ gpg --import public_key.asc
$ gpg --import private_key.asc

Important: add trust

Now edit the key to add ultimate trust:

$ gpg --edit-key <[email protected]>

At the gpg> prompt, type trust, then type 5 for ultimate trust, then y to confirm, then quit.

Now test it with a test file:

$ gpg --sign --encrypt --yes --batch --status-fd 1 --recipient "recipient" --output testfile.gpg testfile.txt

which reports

...
[GNUPG:] END_ENCRYPTION

without adding trust, I get various errors (not limited to the following):

gpg: There is no assurance this key belongs to the named user
gpg: testfile.bin: sign+encrypt failed: Unusable public key

Answer 3

There's an easier way to tell GPG to trust all of its keys by using the --trust-model option:

    gpg -a --encrypt -r <recipient key name> --trust-model always

From the man page:

  --trust-model pgp|classic|direct|always|auto

    Set what trust model GnuPG should follow. The models are:

      always Skip  key  validation  and assume that used 
             keys are always fully trusted. You generally 
             won't use this unless you are using some 
             external validation scheme. This option also 
             suppresses the "[uncertain]" tag printed 
             with signature checks when there is no evidence 
             that the user ID is bound to the key.  Note that 
             this trust model still does  not  allow  the use 
             of expired, revoked, or disabled keys.

Answer 4

This worked for me:

Trying to encrypt a file responds with this:

gpg -e --yes -r <uid> <filename>

It is NOT certain that the key belongs to the person named
in the user ID.  If you *really* know what you are doing,
you may answer the next question with yes.

Use this key anyway? (y/N)

That causes my shell script to fail.

So I:

$gpg --edit-key <uid>

gpg> trust

Please decide how far you trust this user to correctly verify other 
users' keys (by looking at passports, checking fingerprints from 
different sources, etc.)

  1 = I don't know or won't say
  2 = I do NOT trust
  3 = I trust marginally
  4 = I trust fully
  5 = I trust ultimately
  m = back to the main menu

Your decision? 5
Do you really want to set this key to ultimate trust? (y/N) y

Please note that the shown key validity is not necessarily correct
unless you restart the program.

gpg> quit

Now the encrypt works properly.

Answer 5

Add trusted-key 0x0123456789ABCDEF to your ~/.gnupg/gpg.conf replacing the keyid. This is equivalent to ultimately trusting this key which means that certifications done by it will be accepted as valid. Just marking this key as valid without trusting it is harder and either requires a signature or switching the trust-model to direct. If you are sure to only import valid keys you can simply mark all keys as valid by adding trust-model always. In the latter case ensure that you disable automatic key retrieval (not enabled by default).

Answer 6

Based on @tersmitten's article and a bit of trial and error, I ended up with the following command line to trust all keys in a given keyring without user interaction. I use it for keys used with both StackEschange Blackbox and hiera-eyaml-gpg:

# The "-E" makes this work with both GNU sed and OS X sed
gpg --list-keys --fingerprint --with-colons |
  sed -E -n -e 's/^fpr:::::::::([0-9A-F]+):$/\1:6:/p' |
  gpg --import-ownertrust

Personally, I prefer a solution which stores the results in the trustdb file itself rather than depends on user environment outside the shared Git repo.

Answer 7

Here's a trick I've figured out for automation of GnuPG key management, hint heredoc + --command-fd 0 is like magic. Below is an abridged version of one of the scripts that's been written to aid in automation with GnuPG.

#!/usr/bin/env bash
## First argument should be a file path or key id
Var_gnupg_import_key="${1}"
## Second argument should be an integer
Var_gnupg_import_key_trust="${2:-1}"
## Point to preferred default key server
Var_gnupg_key_server="${3:-hkp://keys.gnupg.net}"
Func_import_gnupg_key_edit_trust(){
    _gnupg_import_key="${1:-${Var_gnupg_import_key}}"
    gpg --no-tty --command-fd 0 --edit-key ${_gnupg_import_key} <<EOF
trust
${Var_gnupg_import_key_trust}
quit
EOF
}
Func_import_gnupg_key(){
    _gnupg_import_key="${1:-${Var_gnupg_import_key}}"
    if [ -f "${_gnupg_import_key}" ]; then
        echo "# ${0##*/} reports: importing key file [${_gnupg_import_key}]"
        gpg --no-tty --command-fd 0 --import ${_gnupg_import_key} <<EOF
trust
${Var_gnupg_import_key_trust}
quit
EOF
    else
        _grep_string='not found on keyserver'
        gpg --dry-run --batch --search-keys ${_gnupg_import_key} --keyserver ${Var_gnupg_key_server} | grep -qE "${_grep_string}"
        _exit_status=$?
        if [ "${_exit_status}" != "0" ]; then
            _key_fingerprint="$(gpg --no-tty --batch --dry-run --search-keys ${_gnupg_import_key} | awk '/key /{print $5}' | tail -n1)"
            _key_fingerprint="${_key_fingerprint//,/}"
            if [ "${#_key_fingerprint}" != "0" ]; then
                echo "# ${0##*/} reports: importing key [${_key_fingerprint}] from keyserver [${Var_gnupg_key_server}]"
                gpg --keyserver ${Var_gnupg_key_server} --recv-keys ${_key_fingerprint}
                Func_import_gnupg_key_edit_trust "${_gnupg_import_key}"
            else
                echo "# ${0##*/} reports: error no public key [${_gnupg_import_key}] as file or on key server [${Var_gnupg_key_server}]"
            fi
        else
            echo "# ${0##*/} reports: error no public key [${_gnupg_import_key}] as file or on key server [${Var_gnupg_key_server}]"
        fi
    fi
}
if [ "${#Var_gnupg_import_key}" != "0" ]; then
    Func_import_gnupg_key "${Var_gnupg_import_key}"
else
    echo "# ${0##*/} needs a key to import."
    exit 1
fi

Run with script_name.sh 'path/to/key' '1' or script_name.sh 'key-id' '1' to import a key and assign a trust value of 1 or edit all values with script_name.sh 'path/to/key' '1' 'hkp://preferred.key.server'

Encryption should now be without complaint but even if it does the following --always-trust option should allow encryption even with complaint.

gpg --no-tty --batch --always-trust -e some_file -r some_recipient -o some_file.gpg

If you wish to see this in action, then check the Travis-CI build logs and how the helper script GnuPG_Gen_Key.sh is used for both generating and importing keys in the same operation... version two of this helper script will be much cleaner and modifiable but it's a good starting point.

Answer 8

I think, I figured way to do this. I used 'gpg --import-ownertrust' to export my trust db into a text file then removed all of my keys from it except public key I needed to push. And then imported my public key and edited owner-trust file on to server. This seems like working. Now I am having trouble implementing these steps in Kickstart file:-(

Answer 9

With powershell, here is how to trust [email protected] (adapted from @tersmitten blog post):

(gpg --fingerprint [email protected] | out-string)  -match 'fingerprint = (.+)'
$fingerprint = $Matches[1] -replace '\s'
"${fingerprint}:6:" | gpg --import-ownertrust

Note: using cinst gpg4win-vanilla

Answer 10

There is a way to autotrust key using --edit-key, but without getting into interactive shell (so can be automated in script). Below is a sample for windows:

(echo trust &echo 5 &echo y &echo quit) | gpg --command-fd 0 --edit-key [email protected]

Answer 11

Unix based:

echo -e "5\ny\n" |  gpg --homedir . --command-fd 0 --expert --edit-key [email protected] trust;

For more info read this post. It details if you are creating more than one key.

Answer 12

One way to trust imported gpg keys:

gpg --import <user-id.keyfile>
fpr=`gpg --with-colons --fingerprint <user-id> |awk -F: '$1 == "fpr" {print$10; exit}'`
gpg --export-ownertrust && echo $fpr:6: |gpg --import-ownertrust

here, I assume that you import a key with the <user-id> from <user-id.keyfile>. The second line only extracts fingerprint, you can drop it if you know the fingerprint beforehand.

Answer 13

This oneliner updates the trustdb with the ownertrust values from STDIN -- by extracting the fingerprint to the format required by --import-ownertrust flag.

This flag, as detailed on gpg man page, should be used In case of a severely damaged trustdb and/or if you have a recent backup of the ownertrust values, you may re-create the trustdb.

gpg --list-keys --fingerprint \
    | grep ^pub -A 1 \
    | tail -1 \
    | tr -d ' ' \
    | awk 'BEGIN { FS = "\n" } ; { print $1":6:" }' \
    | gpg --import-ownertrust

Answer 14

echo "$( gpg --list-keys --fingerprint | grep "your-key-name-here" -B 1 | head -1 | tr -d '[:space:]'|awk 'BEGIN { FS = "=" } ; { print $2 }' ):6:" | gpg --import-ownertrust;

This one-liner is pulled from this gist

Just replace "your-key-name-here" with the name of your key.

Answer 15

Try this :

(echo trust &echo 5 &echo y &echo quit &echo save) | gpg --homedir 'gpgDirectory/' --batch --command-fd 0 --edit-key 'youKey'

--homedir : not required