[Encryption technique for linkable anonymizing].

Abstract

Linkage of different records such as health insurance claims or medical records for the purpose of cohort studies or cancer registration usually requires matching with personal names and other personally identifiable data. The present study was conducted to examine the possibility of performing such privacy-sensitive procedures in a "linkable anonymizing" manner using encryption. While bidirectional communication entails encryption and deciphering, necessitating both senders and receivers sharing a common secret "key", record linkage entails only encryption and not deciphering because researchers do not need to know the identity of the linked person. This unidirectional nature relieves researchers from the historical problem of "key sharing" and enables data holders such as municipal governments and insurers to encrypt personal names in a relatively easy manner. The author demonstrates an encryption technique using readily available spread-sheet software, Microsoft Excel in a step-by-step fashion. Encoding Chinese characters into the numeric JIS codes and replacing the codes with a randomly assigned case-sensitive alphabet, all names of Japanese nationals will be encrypted into gibberish strings of alphabet, which can not be deciphered without the secret key. Data holders are able to release personal data without sacrificing privacy, even when accidental leakage occurs and researchers are still able to link records of the same name because encrypted texts, although gibberish, are unique to each name. Such a technical assurance of privacy protection is expected to satisfy the Privacy Protection Act or the Ethical Guidelines for Epidemiological Research and enhance public health research. Traditional encryption techniques, however, cannot be applied to cancer or stroke registration, because the registrar receives reports from numerous unspecified senders. The new public key encryption technique will enable disease registry in a linkable anonymizing manner. However various technical problems such as complexity, difficulties in registrar inquiries and risk of code-breaking make the encryption technique unsuitable for disease registry in the foreseeable future.