Here’s a question worth asking… If you swapped out the reader on your front door tomorrow with a reader from a different manufacturer, would the access credential already stored on your smartphone still work?
For most people, the honest answer is no. And the reason usually comes down to something far less visible: the cryptography a mobile credential is built on.
Is the access credential made up of a singular secret key that is shared or a public/private key pair? This will determine the level of true interoperability.
The interoperability problem hiding in plain sight
A mobile access credential is, at its core, a small piece of cryptographic identity issued to one person’s phone. It’s meant to travel with that person, proving who they are at whatever door, reader, or system it encounters. But most credentials in use today aren’t actually built to travel. They’re built to work with one system, and one system only, because of how they’re secured.
Think about what that means for the person actually carrying the credential. An employee who moves between properties in the same portfolio may need a different credential for each one, not because their identity changed, but because the credential itself was never designed to be recognized outside the system that issued it.
The half of the story nobody talks about
Here’s what most conversations about interoperability leave out: It’s decided by what the credential itself is built on, cryptographically, and that decision determines everything else about where it can and can’t be used.
Most legacy credentials are built on symmetric cryptography. The credential carries a secret key, and the reader it’s presented to holds a copy of that exact same secret. A credential built this way is only ever recognizable to a reader that was handed the same secret in the first place. Present it to any other system, and there’s nothing for that system to check it against. The credential isn’t identifying itself. It’s just proving it knows a password that only one set of readers was ever told.
Asymmetric cryptography builds the credential differently. It carries a private key that never leaves the secure element in the device it lives on, and that private key is paired with a public key that can be shared openly without weakening the credential at all. Because verifying the credential only requires that public key, any system that has the public key can check it. The credential becomes something that can prove its own identity on its own terms, rather than something that only makes sense to whoever was let in on its secret.
This is the difference between a credential that’s portable by design and one that only works where it was told to.
One mobile credential, access to multiple systems
This is exactly what Sentry Interactive builds its mobile access credentials around. Each one is secured with asymmetric public key cryptography rather than a shared symmetric key, so the credential itself carries the ability to be verified independently, rather than depending on a secret shared in advance with one vendor’s readers. That’s what lets the same credential move across and unify a portfolio of different access control brands and hardware generations, connecting via cloud services into whatever system it encounters. This means a user does not have to juggle multiple credentials to access multiple buildings with different access control hardware installed, they can use just a single open standard mobile credential stored securely on their device.
Credentials that aren’t dictated by reader hardware
Next time a vendor tells you their mobile credential is “interoperable,” ask two questions instead of one. Would this specific credential still work if the reader behind it changed? And could a different system verify it without ever being handed a copy of its private key?
A credential built on a shared secret only works within the boundary of whoever holds that secret. A credential built on asymmetric cryptography can prove itself anywhere, because it was never depending on the secret being shared in the first place.
If the answer to either question is no, what’s being sold as an “interoperable credential” is really just a key that only fits one lock.
