iphoneToday Apple announced that the iPhone 5S will have a fingerprint scanner. Many of us in the security community are highly sceptical of this feature, while others saw this as a smart security move. Then of course there are the journalists who see fingerprints as the ultimate password killer. Clearly there is some disagreement here. I thought I’d lay this out for those of you who need to better understand the implications of using fingerprints vs or in addition to passwords.

Biometrics, like usernames and passwords, are a way to identify and authenticate yourself to a system. We all know that passwords can be weak and difficult to manage, which makes it tempting to call every new authentication product a password killer. But despite their flaws, passwords must always play some role in authentication.

The fact is that while passwords do have their flaws, they also have their strengths. The same is true with biometrics. You can’t just replace passwords with fingerprints and say you’ve solved the problem because you have introduced a few new problems.

To clarify this, below is a table that compares the characteristics of biometrics vs passwords, with check marks where one method has a clear advantage:

Passwords Biometrics
Difficult to remember Don’t have to remember 
Requires unique passwords for each system Can be used on every system 
Nothing else to carry around Nothing else to carry around
Take time to type Easy to swipe/sense 
Prone to typing errors Prone to sensor or algorithm errors
Immune to false positives  Susceptible to false positives
Easy to enroll  Some effort to enroll
Easy to change  Impossible to change
Can be shared among users 1  Cannot be shared 
Can be used without your knowledge Less likely to be used without your knowledge 
Cheap to implement  Requires hardware sensors
Work anywhere including browsers & mobile  Require separate implementation
Mature security practice  Still evolving
Non-proprietary  Proprietary
Susceptible to physical observation Susceptible to public observation
Susceptible to brute force attacks Resistant to brute force attacks 
Can be stored as hashes by untrusted third party  Third party must have access to raw data
Cannot personally identify you  Could identify you in the real world
Allow for multiple accounts  Cannot use to create multiple accounts
Can be forgotten; password dies with a person Susceptible to injuries, aging, and death
Susceptible to replay attacks Susceptible to replay attacks
Susceptible to weak implementations Susceptible to weak implementations
Not universally accessible to everyone Not universally accessible to everyone
Susceptible to poor user security practices Not susceptible to poor practices 
Lacks non-repudiation Moderate non-repudiation 
1 Can be both a strength and a weakness


What Does This Tell Us?

As you can see, biometrics clearly are not the best replacement for passwords, which is why so many security experts cringe when every biometrics company in their press releases claim themselves as the ultimate password killer. Biometrics do have some clear advantages over passwords, but they also have numerous disadvantages; they both can be weak and yet each can be strong, depending on the situation. Now the list above is not weighted–certainly some of the items are more important than others–but the point here is that you can’t simply compare passwords to biometrics and say that one is better than the other.


It’s not clear, however, if the Apple implementation will allow for you to use both a fingerprint and password (or PIN) together.

Now specifically talking about the iPhone’s implementation of a fingerprint sensor, there are some interesting points to note. First, including it on the phone makes up for some of the usual biometric disadvantages such as enrollment, having special hardware sensors, and privacy issues due to only storing that data locally. Another interesting fact is that the phone itself is actually a third factor of authentication: something you possess. When combined with the other two factors it becomes an extremely reliable form of identification for use with other systems. A compromise would require being in physical possession of your phone, having your fingerprint, and knowing your PIN.

Ultimately, the security of the fingerprint scanner largely depends on the implementation, but even if it isn’t perfect, it is better than those millions of phones with no protection at all.

There is the issue of security that some have brought up: is this just a method for the NSA to build a master fingerprint database? Apple’s implementation encrypts and stores fingerprint locally using trusted hardware. Whether this is actually secure remains to be seen, but keep in mind that your fingerprints aren’t really that private: you literally leave them on everything you touch.




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