How to determine fingerprint of imported OpenPGP key in PHP using the GnuPG module?

Question

In php I have a public key, but I do not know fingerprint of this key. How can I encrypt a text by this public key?

Here is the code:

$gpg = new gnupg();
putenv("GNUPGHOME=/tmp");
$pubkey = "-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v2
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=Mgfi
-----END PGP PUBLIC KEY BLOCK-----
";


$info = $gpg->import($pubkey);
print_r($info);
$gpg->addencryptkey("96E9C3DC001C10B3AE6236B1FEFD88729C9BDD27");
$enc = $gpg->encrypt("just a test");

echo $enc;

I do not know this encryptkey :

$gpg->addencryptkey("96E9C3DC001C10B3AE6236B1FEFD88729C9BDD27");

How can I get this fingerprint from public key?

Answer 1

Generally, running gpg --list-keys --with-fingerprint --with-colons piping in the key will yield information on the key. You will get an easily parseable result like

pub:-:2048:1:FEFD88729C9BDD27:2015-09-27:::-:mytest <aa@aa.aa>:
fpr:::::::::96E9C3DC001C10B3AE6236B1FEFD88729C9BDD27:
sub:-:2048:1:22EC13225E681EFA:2015-09-27::::

The fingerprint is at a fixed column in the second line of the colon-separated output.

But when you're importing the key anyway, have a look at the output given by the code in your question, which already contains the fingerprint in $info :

Array
(
    [imported] => 1
    [unchanged] => 0
    [newuserids] => 0
    [newsubkeys] => 0
    [secretimported] => 0
    [secretunchanged] => 0
    [newsignatures] => 0
    [skippedkeys] => 0
    [fingerprint] => 96E9C3DC001C10B3AE6236B1FEFD88729C9BDD27
)

Importing a key anyway to receive it's fingerprint is a viable way probably not too expensive, you might even be able to somehow cache the fingerprints for the hashed keys. Calculating the fingerprint on your own is something possible, but would require writing your own OpenPGP parser code which is probably not something you want to do.