The recently introduced legislation on data retention to aid prosecuting cyber-related crime in Europe also affects the achievable security of systems for anonymous communication on the Internet. We have analyzed the newly arising risks associated with the process of accessing and storage of the retained data and propose a secure logging system, which utilizes cryptographic smart cards, trusted time stamping servers and distributed storage. These key components will allow for controlled access to the stored log data, enforce a limited data retention period, ensure integrity of the logged data, and enable reasonably convenient response to any legitimated request of the retained data. A practical implementation of the proposed scheme was performed for the AN.ON anonymity service, but the scheme can be used for other services affected by data retention legislation.