What is Biometric Data?

30 September 2025

Biometric data is everywhere. From unlocking your phone with your face to passing through airport security using your fingerprint, biometrics have become part of our daily lives. But what exactly is biometric data, and why does it matter?
In this blog, we’ll break it down simply, explain where it’s used, and why it’s both powerful and sensitive. The initial answer to the question "what is biometric data?" is simple, but the nuances between different types of biometric data are much more intricate.

Biometric Data Definition

Biometric data refers to unique physical or behavioural characteristics that can be used to identify an individual. Common types include:
  • Fingerprints.
  • Facial features.
  • Iris or retina patterns.
  • Voice.
  • Hand geometry.
  • Behavioral traits like the way you walk or type.
This kind of data is collected by sensors, cameras, or microphones and is used to create a “biometric template”. That template is then used to verify or authenticate your identity in a variety of situations - from logging into your banking app to verifying your passport at the airport.

What is Biometric Data Used For?

Biometric data is used in both security and convenience-driven applications. Some of the most common include:
  • Device unlocking: Face ID and fingerprint unlocks are biometric systems.
  • Digital onboarding: Verifying identity for opening bank accounts or signing up for services.
  • Airport border control: Biometric passports use facial or fingerprint data to speed up immigration.
  • Payment verification: Allowing users to authorise payments using biometrics.
  • Workforce management: Used for clocking in and out, especially in secure environments.
Because biometric data is so personal, it offers the highest level of identity assurance.  It's much harder to fake someone's face or fingerprint than it is to guess their password.

What is a Biometric Data Passport?

When we talk about a biometric data passport, we usually mean a travel document that includes biometric information stored in an embedded chip. Most modern passports include:
  • A digital image of your face.
  • Your full name, date of birth, and nationality.
  • Sometimes, fingerprints or iris scans.
This data is used to verify your identity at border control gates and reduce the risk of document fraud. Biometric passports are now standard in most countries and have helped to speed up security checks without compromising on safety.

Is Biometric Data Secure?

Here’s the tricky part: biometric data is powerful, but it's also sensitive.
Unlike a password, you can’t change your face or fingerprint. So if biometric data is compromised, the consequences can be serious and long-lasting.
Biometric systems store data in one of two ways - either on a server or on a device. Each of these comes with risks:
  • Server breaches: If biometric templates are stored in unencrypted form on a server, they can be stolen in a data breach.
Fact: Hashed biometric data is still insecure, as biometric hashes can be reverse-engineered to reveal the original biometric template beneath. To find out more about this, you can check out our Technical White Paper here.
  • Device manipulation: Local storage methods, like FaceID, can be tricked if someone changes the face registered to the FaceID account.
That’s why how and where biometric data is stored and processed matters just as much as what it is.

The Problem with Device-Bound Biometrics

Device-bound or ‘local’ biometrics keep biometric data on the device. FaceID is a common example.
For example, if a banking app uses FaceID to protect their Logins, the bank app asks the device to scan the user’s face. However, this face is not tied to the credentials that were used to set up the bank account. Instead, the device checks that the person’s face matches the one that was used to set up FaceID. If someone were to add their face to the FaceID account - a common family fraud use case - someone else could log into their account.
Device-bound biometrics are private, but they are not secure.

The Problem with Centralised Biometrics

In centralised systems, biometric data is stored and verified in one location - usually a cloud server. Crucially, they check that the person authenticating has the same face as the face used to sign up to a bank - that has passed the KYC check. While this makes authentication more secure, it also introduces privacy risks.
If someone gains access to the central database, they can potentially steal thousands of biometric profiles. And unlike a password reset, those profiles can’t be changed.
Centralized biometrics are secure, but not private.
Many organisations are now looking for alternative approaches that don’t put all biometric data in one place.

Decentralised Biometrics: A Safer Alternative?

Decentralised biometrics are often seen as the answer to the privacy problems of centralised systems. But it’s important to understand what this really means.
According to Gartner, decentralised biometric systems are those that aren’t fully local (like FaceID) or fully centralised (like cloud-based storage). In theory, they offer the privacy of local biometrics and the security of centralized biometrics.
In practice, however, many systems claiming to be decentralised still rely on a set of vendor-controlled servers that store fragmented biometric data. This technique, called sharding, spreads pieces of biometric data across multiple locations - but if those servers are owned by the same company, it’s not truly private.

What Makes Biometric Data Truly Private?

To keep biometric data private, you need a system that doesn’t store or reconstruct the data at all. That’s where Zero-Knowledge Biometrics™ (ZKB) comes in.
ZKB is a privacy-preserving approach unique to Keyless that uses secure Multi-Party Computation (MPC). This allows biometric data to be matched without being shared or stored - even by the vendor.
Here’s how it works: 
To enroll, a user takes a selfie. Their biometric data is transformed on the device into a cryptographic representation. Then, that is sent to the server. This keeps the data private on the server - even if it were compromised, there’s nothing usable to steal. 
To authenticate, a user takes another selfie. This again is transformed on the device and compared to the original cryptographic representation on the server. The two cryptographic representations are compared, and if they match, the user is authenticated.
Unlike centralized biometrics, biometric data isn’t matched; but cryptographic representations instead. Keyless itself does not see the biometric data itself.
This makes ZKB the most secure and private ways to manage biometric authentication today.

Why Biometric Data Matters More Than Ever

As we shift to passwordless systems, biometric data plays a growing role in digital identity. But with this growth comes new responsibility. Organisations need to:
  • Protect biometric data at every stage: in use, in transit, and at rest.
  • Comply with privacy laws like GDPR, which treat biometric data as a special category.
  • Choose vendors that use truly privacy-preserving technology - not just ones that say they do.
Whether you're verifying a user for a payment, onboarding them to a service, or authenticating them at login, understanding what biometric data is and how to protect it is key.

Final Thoughts

Biometric data is one of the most powerful tools in modern identity systems. But with great power comes the need for responsible handling. The good news is, new technologies like ZKB are showing that it’s possible to combine strong security with true privacy.
So the next time someone asks "what is biometric data?", you’ll know: it’s more than just a face or a fingerprint. It’s a digital key to your identity - and it needs to be protected as such.
To find out how Keyless can help your organization prevent ATOs, improve UX, and protect your bottom line, schedule a personalised demo today.
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