The use of fingerprint scanning for access control is a common application of biometric technology that is becoming increasingly common due to its ease of use and security. Users can easily swipe a finger to access a smartphone or laptop instead of typing a password, and unlike passwords, biometrics cannot be written down and shared across users. However, when a biometric template is compromised, a user cannot grow a new fingerprint or change their iris in the same way they can change a password. Revocable template techniques improve security by enabling an organization to revoke the existing biometric based security token and reissue the token without modifying the under lying biometric.
How Biometric Matching Works
Biometric matching uses templates to convert an image of a biometric trait, such as a fingerprint or iris image, into a searchable set of data. This process is known as the minutia extraction process. For a fingerprint image, points of interest–such as where fingerprint ridges end, converge, or split–are marked by an algorithm or human fingerprint examiner. These points are then mapped in relation to the center of the fingerprint. The resulting map of minutia points is simply a set of coordinates that computers can quickly search using matching algorithms that return scores that indicate how closely sets of data match. If the score is above an established threshold, the fingerprints are determined to be from the same finger.
Revocable Features Improve Security of Biometric Templates
In order for a system that is based on biometric template matching to be effective, the template matching needs to be accurate, secure, and address privacy concerns. For a system that uses biometric templates for identity management, there is also the issue of what do to when a template has been compromised. For a password based system, the solution to this problem is straightforward. The user creates a new password and the problem is solved. However, if the security token is based solely on one biometric–such as a fingerprint for access to a laptop–one cannot simply instruct the user to grow new fingerprints.
Revocable features are biometric templates that have been enhanced through several different methods to allow the controlling organization to revoke the existing biometric based security token and reissue the token without modifying the under lying biometric. Salting and one-way transformations are two general methods that researchers are looking at to create revocable templates.
- Salting allows compromised biometric templates to be recovered: Salting is a technique that is adapted from methods used to prevent easy passwords from being vulnerable to brute force attacks. The process adds a predetermined random set of characters to every password in order to increase their complexity. In regards to revocable biometric templates, salting refers to inserting a known set of fake data into predetermined locations of the template to disguise the template. The system owner knows the location and content of this inserted fake data. If the template is compromised, this data can be changed and the existing template is invalidated.
- One-Way Transformations support increased privacy and security: One-way encryption transforms the feature set using a known distortion pattern. This technique distorts the biometric templates in a revocable but non-reversible manner which has advantages in regards to privacy. The system uses advanced mathematical algorithms to perform these transformations and they can be performed in a manner so that it is very difficult to determine that any transformations have occurred. Matching software can then process the distorted biometric templates in the same way normal templates would be processed.
As the use of biometric templates in access control grows, so does the security surrounding it. Biometric templates provide an efficient, secure method to control access to resources within an organization and revocable template techniques address the problem of reissuing a security token when a biometric based token has been compromised.
About the Author: Mike Wagner is an IEEE Certified Biometric Professional and has performed biometrics development on projects such as US-VISIT and the system used by the Border Patrol to collect biometric data in the field. In addition to his focus in biometrics, Mike Wagner also specializes in enterprise architecture, Java software development, large system troubleshooting and problem solving.