Crypt/GPG/Key.php
public function getPrimaryKey()
    {
        $primary_key = null;
        if (count($this->_subKeys) > 0) {
            $primary_key = $this->_subKeys[0];
        }
        return $primary_key;
    }
public function getPrimaryKey()
    {
        $primary_key = null;
        if (count($this->_subKeys) > 0) {
            $primary_key = $this->_subKeys[0];
        }
        return $primary_key;
    }
Gets the primary sub-key of this key

The primary key is the first added sub-key.

@return Crypt_GPG_SubKey the primary sub-key of this key.