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Anonymity Project |
The work reported herein provides a framework for reasoning about and assessing
proposed technical solutions that may answer this question. Eight categories of technologies
(encoding, hashing, encryption, scan cards/RFID, biometrics, consent, inconsistent hash, and
distributed query) are examined and a set of recommendations provided. Results suggest that
inconsistent hashing, distributed query and (regular) hashing may be easier to bundle with
policies and best practices to create an effective solution. Scan cards, encryption, and biometrics
create new kinds of risks to consider. Consent and encoding are technically the simplest to
implement but harbor serious dangers that are difficult for any particular implementation to
overcome. Biometrics is the only technology that authenticates clients; all the other technologies
tend to rely on non-verified information from clients. While significant differences and tradeoffs
exist in the use of these technologies, there is no magic technology as much as practices that
must be bundled with any chosen technology in order to demonstrate minimal risk of client reidentification
and maximum correctness in computing an unduplicated accounting.
In an attempt to perform a national unduplicated accounting of visit patterns across domestic
violence homeless shelters, while respecting the confidentiality of the clients who are the
subjects of that accounting, the United States Department of Housing and Urban Development
("HUD") has sponsored locally administered Homeless Management Information Systems
("HMIS"). These are computerized data collection and processing systems designed to capture
person-specific information over time from homeless persons being serviced by local shelters. In
order to maintain client safety and to insure high degrees of compliance, HUD agreed that the
name and Social Security number of each client of a domestic violence homeless shelter are not
to be forwarded to HMIS. Instead, a newly created identifier termed a “unique identification
number ("UID") can be used. A question posed is, "how do shelters construct UIDs with
minimal risk of re-identification while still achieving an accurate unduplicated accounting?"
L. Sweeney
Risk Assessments of Personal Identification Technologies for Domestic Violence Homeless Shelters.
Carnegie Mellon University, School of Computer Science. Technical Report CMU-ISRI-05-133. Pittsburgh: November 2005.
Data Privacy Lab Working Paper 901. Pittsburgh 2005.
(PDF).
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