Keyman is a key manager for storing Freenet SVK keys; it keeps all SVK private keys in a encrypted form. This could even work with any type of public/private key encryption (although it focuses on Freenet) and can hopefuly be extended so it can use any future Freenet public/private key types.
Standards-compliant Java persistence via JDO/JPA/REST and RDBMS/db4o/Excel/LDAP.