You might want to take a look at Crypt::OpenPGP. It's a pure Perl implementation of the OpenPGP standard and is compatible with PGP2, PGP5, GnuPG, etc.

Sample usage:

    use Crypt::OpenPGP;
    my $pgp = Crypt::OpenPGP->new( PubRing => $pubring);
    my $ciphertext = $pgp->encrypt(
                   Data       => $data,
                   Recipients => $key_id,
                   Armour     => 1,
             );
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