A Nearly Tight Bound for Private Information Retrieval Protocols

We show that any 1-round 2-server Private Information Retrieval Protocol where the answers are 1-bit long must ask questions that are at least n− 2 bits long, which is nearly equal to the known n−1 upper bound. This improves upon the approximately 0.25n lower bound of Kerenidis and de Wolf while avoiding their use of quantum techniques.