4. Where personal data are processed for archiving purposes in the public interest, Union law, which may include internal rules adopted by Union institutions and bodies in matters relating to their operation, may provide for derogations from the rights referred to in Articles 17, 18, 20, 21, 22 and 23 subject to the conditions and safeguards referred to in Article 13 in so far as such rights are likely to render impossible or seriously impair the achievement of the specific purposes, and such derogations are necessary for the fulfilment of those purposes.