Present health care information and communication systems sufficiently respect neither the interests of the professional users (physicians, nurses, etc.) nor those of the usees (patients) concerning informational self-determination, integrity, and non-repudiation. The EU-AIM-SEISMED project has attacked this challenge. There is consensus that legal regulations and organisational measures around health care IT-systems have to be revisited and harmonised. However, the increasing processing capacities of IT-systems demand that the legitimate security interests of users and usees are enforced in advance — not only after the fact. This cannot be achieved against IT-systems but only by the help of IT-systems. Since cryptographic mechanisms are an essential tool to this end SEISMED provides guidelines and technical recommendations on cryptographic mechanisms.