A method, a system, a registry, a repository and a computer program product are disclosed for securely accessing sensitive medical data records stored in a repository. Before accessing security-critical data in the repository, a registration inquiry with a separate registry must be carried out in order to obtain a security token having limited temporary validity, for example in the form of a barcode. A data source and/or a data sink can then use the security token to access the security-critical data in that an index module indexes the data record inquired about on the repository.