Biometrics are being pegged as the next big deal for user authentication, esp. within the banking & financial sectors. Been having a few discussions to understand how good biometric authentication are as compared to traditional Pins? Is a return to being angootha-chaaps (thumb-print based) for all purposes the right thing to do, technically that is? Here's a lay-man attempt at answering some of those questions.
Staring off by calling out known facts & assumptions about thumb-prints (an example biometric):
That's enough background information for a rough evaluation. A thumb-print scan of a certain size, say 10Kb is just a string of 10,000 bits of 0s & 1s. This is unique to an individual & stays the same over the individual's lifetime.
A 4-digit Pin on the other hand is a combination of four Integer numbers. Each Integer typically gets encoded into a 32-bit string. A 4-digit Pin is therefore a 4 * 32-bit = 128-bit string. The Pin normally stays the same, unless explicitly changed (rather infrequent).
In simplistic terms, when a request to authenticate an individual is made to a computer, it reads the incoming string of bits (from the Pin or the thumb-print) & matches it against a database of known/ all existing (1-to-1 or 1-to-N matches) strings. To the computer other than the difference in length between the two encoded strings of thumb-print (10,000-bit) & Pin (128-bit), there's not much difference between the two.
On the other hand, the Pin seems much better than the thumb-print if it were ever to get compromised due to a breach or a malicious app or something. The Pin can simply be changed & a new 128-bit string can replace the earlier one going forward. But in the case of the thumb-print there's really nothing that can be done as the individual's thumb-print scan will stay the same over time!
Yet another alternative for authentication is to use One Time Password (OTP). The OTP is also a 4-digit number (128-bit string) but it is re-issued each time over a separate out-of-band channel (such as SMS), is short lived, & is valid for just one use. These features make the OTP way more robust & immune to breaches & compromise.
What is a biometric to the human being, is just another string of bits to the machine, very similar to the string of bits of a Pin or an OTP. From the stand-point of safety though, the OTP is far superior to the other two. As is the common practice, it maybe ok to use biometric authentication within environments such as government offices, airports, etc. where the network is tightly regulated & monitored. For end-user authentication however, such as within phone apps, or internet payments, or other channels where the network or device is orders of magnitude more insecure & vulnerable these are not ideal. In general OTPs should be the top pick & biometrics the last option in such cases:
OTP > Pin > Biometrics
Staring off by calling out known facts & assumptions about thumb-prints (an example biometric):
- Thumb-prints are globally unique to every human being.
(Counter: Enough people who don't have/ lose a thumb, or lose their thumb-prints due to some other reason. Also partial thumb-prints of two individuals taken of a portion of the thumb due to faults at the time of scanning, etc. may match.)
- Thumb-prints stay consistent over the lifetime of an individual (adult).
(Counter: May not be true due to physical changes in the human body, external injuries, growths, etc.)
- Computers are basically binary machines. So whether it's a document (pdf, doc), an image file (jpg, gif, etc.), a video (mp4), a music file (wav), a Java program, a Linux operating system, etc. all of the data, instructions, etc. get encoded into a string of bytes (of 0s & 1s).
- The thumb-print scan of an individual is similar to an image file (following a standard protocol), encoded as a string of bytes.
The thumb-prints scans of two different individuals will result in two different strings of bytes, that are unique to the individual.
Subsequent scans of the thumb-print of the same individual will result in exactly the same string of bytes over-time.
That's enough background information for a rough evaluation. A thumb-print scan of a certain size, say 10Kb is just a string of 10,000 bits of 0s & 1s. This is unique to an individual & stays the same over the individual's lifetime.
A 4-digit Pin on the other hand is a combination of four Integer numbers. Each Integer typically gets encoded into a 32-bit string. A 4-digit Pin is therefore a 4 * 32-bit = 128-bit string. The Pin normally stays the same, unless explicitly changed (rather infrequent).
In simplistic terms, when a request to authenticate an individual is made to a computer, it reads the incoming string of bits (from the Pin or the thumb-print) & matches it against a database of known/ all existing (1-to-1 or 1-to-N matches) strings. To the computer other than the difference in length between the two encoded strings of thumb-print (10,000-bit) & Pin (128-bit), there's not much difference between the two.
On the other hand, the Pin seems much better than the thumb-print if it were ever to get compromised due to a breach or a malicious app or something. The Pin can simply be changed & a new 128-bit string can replace the earlier one going forward. But in the case of the thumb-print there's really nothing that can be done as the individual's thumb-print scan will stay the same over time!
Yet another alternative for authentication is to use One Time Password (OTP). The OTP is also a 4-digit number (128-bit string) but it is re-issued each time over a separate out-of-band channel (such as SMS), is short lived, & is valid for just one use. These features make the OTP way more robust & immune to breaches & compromise.
What is a biometric to the human being, is just another string of bits to the machine, very similar to the string of bits of a Pin or an OTP. From the stand-point of safety though, the OTP is far superior to the other two. As is the common practice, it maybe ok to use biometric authentication within environments such as government offices, airports, etc. where the network is tightly regulated & monitored. For end-user authentication however, such as within phone apps, or internet payments, or other channels where the network or device is orders of magnitude more insecure & vulnerable these are not ideal. In general OTPs should be the top pick & biometrics the last option in such cases:
OTP > Pin > Biometrics
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