Shankar Raghavan (PMP student University of Washington)
Biometrics are data obtained from a person based on his or her physiological or behavioral characteristics. Biometric data is attractive in the field of cryptography for uniquely identifying and authenticating a person or to be used as a key for encrypting data that can be uniquely decrypted by the same person later. These two areas are the focus of this paper.
Why biometrics for authentication?
Biometrics have the advantages of being a. unique for a person with no chance of unintentional duplication, b. much longer and random compared to a password that is within the ability of a human to remember, and most importantly, c. its always conveniently there with the person. The symmetric and asymmetric keys are impossible to be remembered in the human brain. The convenience of neither having to remember anything, nor carry anything, makes biometric authentication a very attractive proposition.
Fingerprint, facial images, iris recognition, retinal scanning, hand geometry, voice and signatures are the popular biometric technologies used. Umut et al  give a comparison of the different biometric identifiers and the table below summarizes that:
Distinctiveness: Can people be distinguished based on that identifier?
Permanence: Does the identifier change its features with time?
Performance: How accurate is the technique and how fast can it measure?
Acceptability: Willingness of people to use it.
Fingerprints are one of the oldest forms of biometric identifiers and continue being the most frequently deployed biometric system due to their proven track record. Finger prints are unique to each person (even identical twins) and each finger. The basis for identification was primarily based on minutiae that mark ends or bifurcation of ridges and shown as the white lines in fig 1 below. The orientation and location of these minutiae is recorded and compared. About 10-11 minutiae are sufficient in uniquely identifying a person. An elaborate indexing system known as the “Henry system” was also used widely later and is adopted by computer based identification schemes for classification. The minutiae form a triplet (x, y, θ), where x and y are their location (of the point of ridge ending or bifurcation) and θ is the point of orientation of the minutiae (as if the ridge continued in the ridge ending case).
Fig 1 Iris scans analyze the features that exist in the colored tissue surrounding the pupil which has more than 200 points that can be used for comparison, including rings, furrows and freckles. The scans use a regular video camera style and can be done from further away than a retinal scan. The uniqueness of eyes, even between the left and right eye of the same person, makes iris scanning very powerful for identification purposes. The likelihood of a false positive is extremely low and its relative speed and ease of use make it a great potential biometric. The only drawbacks are the potential difficulty in getting someone to hold their head in the right spot for the scan if they are not doing the scan willingly.
Retinal scanning analyses the layer of blood vessels at the back of the eye. Scanning involves using a low-intensity light source and an optical coupler and can read the patterns at a great level of accuracy. It does require the user to remove glasses, place their eye close to the device, and focus on a certain point. This has been the main drawback as users feel uncomfortable with agreeing to be examined in this manner.
Hand geometry involves measurements of the human hand, including its shape, and lengths and widths of the fingers, can be used as biometric characteristics. However this may not be invariant over the lifespan of an individual.
The other types of scan are not described further in this paper as they may not be as widely used in the future.