Dmitri Asonov Johann Christoph Freytag Almost Optimal Private Information Retrieval. 209-223 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2482&spage=209 2002 conf/pet/2002 Privacy Enhancing Technologies db/conf/pet/pet2002.html#AsonovF02