Hashing on strings, cryptography, and protection of privacy

Summary form only given. The issues of privacy and reliability of personal data are of paramount importance. If L is a list of people carrying some harmful defective gene, we want questions as to whether a person is in L to be reliably answered without compromising the data concerning anybody else. Reliability means that once the list is formed, nobody can play with the answer. Thus the answer should be checkable by the agent posing the question. We present an efficient protocol for this task. Our solution has very strong privacy protection properties.