Crypt/GPG.php
public function addEncryptKey($key)
    {
        $this->_addKey($this->encryptKeys, true, false, $key);
        return $this;
    }
public function addEncryptKey($key)
    {
        $this->_addKey($this->encryptKeys, true, false, $key);
        return $this;
    }
Adds a key to use for encryption

@param mixed $key the key to use. This may be a key identifier, user id
user id, fingerprint, {@link Crypt_GPG_Key} or
{@link Crypt_GPG_SubKey}. The key must be able to
encrypt.

@return Crypt_GPG the current object, for fluent interface.

@see Crypt_GPG::encrypt()
@see Crypt_GPG::encryptFile()
@see Crypt_GPG::clearEncryptKeys()
@see Crypt_GPG::_addKey()