GhostDB is a relational database engine embedded on a secure USB key (a large Flash persistent store combined with a tamper and snoop-resistant CPU and small RAM) that allows linking private data carried on the USB Key and public data available on a public server  . GhostDB ensures that the only information revealed to a potential spy is the query issued and the public data accessed (See Section 6.4 ). Queries linking public and private data entail novel distributed processing techniques on extremely unequal devices and in which data flows in a single direction: from public to private. The GhostDB prototype has been developed in C and currently runs on a software simulator of the USB device. This simulator is I/O accurate, meaning that it delivers the exact number of pages read and written in Flash, thus allowing assessing the GhostDB performance. The GhostDB prototype has been recently demonstrated at the VLDB'07 and BDA'07 conferences  .