For authentication of diploma make a request to the educational institution in which was issued the certificate or document. Often, however, Universities refuse to give such information as it confidential. The only way out of this situation – drafting a formal letter on company letterhead stating the purpose of the check and the signature of the passport holder.
Not every employer has the ability to test, since the information about the owner of the diploma is limited and cannot be obtained without request. If you have friends in the police, then the best way to check would be the query to the law enforcement authorities.
You can use social networks that have an extensive database of educational institutions through which you will be able to find class mates of the candidate and everything to learn from them.
Many fake certificates and degrees are not really fakes, as they are bought directly at the University and have relevant records, so the only way to verify the authenticity of the diploma – verification of appropriate knowledge of the applicant.