Core capabilities
To learn more about Mobile Credentials, we will revisit the Kingdom of Kākāpō, where digital trust ecosystems are commonly embedded into everyday interactions.
Issuer authentication
The Kākāpō Transport Agency (KTA) issues mobile drivers licences (mDLs) as Mobile Credentials. They are an issuer in this ecosystem. For Kākāpō verifiers to trust mDLs, Mobile Credentials must enable authenticating their issuers.
To enable this, when the KTA issues and signs an mDL it adheres to the ISO/IEC 18013-5:2021 standard, a very specific and well-defined suite of data structures, interfaces, protocols and certificate profiles.
Verifiers can authenticate the origin of an mDL via a chain of certificates linked within the mDL, all the way to its root certificate.
Refer to The Chain of Trust sub-section for more information.
In-person exchange
Emma Tasma has been issued an mDL as a Mobile Credential by the KTA, and saves it to a digital wallet installed on her mobile device. She is a holder in this ecosystem.
When Emma gets pulled over by a police officer for routine inspection, she uses her digital wallet to present a QR code to the police officer for scanning and verifying her drivers licence. The QR code is used to establish a wireless communication channel between Emma's digital wallet and the police officer's device. This secure end-to-end encrypted channel is then used to transmit Emma's mDL as a Mobile Credential for verification.
The police officer is a verifier in this ecosystem, and this verification workflow is an example of an in-person exchange.
Device authentication
The police officer needs to ensure that the presented mDL was issued to Emma's device.
To protect against malicious mDL cloning, Mobile Credentials are bound to a device and enable verifying the binding between a credential and the mobile device used to present it. We refer to this concept as device authentication.
The receiving mobile device generates a private key that is locked to its tamper resistant key store when the credential is issued. The issuer then includes the corresponding public key in the mDL to establish the device binding. That same private key must be used whenever the credential is presented to a verifier.
Emma uses her digital wallet to present her mDL, and upon verification the police officer can be sure that Emma is presenting a KTA issued licence that was issued to her device.
Holder authentication
As Mobile Credentials are high assurance credentials, it is not enough to authenticate that the credential is presented using the device it was issued to. The officer must also verify that the person presenting the mDL is actually Emma Tasma.
For this purpose, Mobile Credentials can include a portrait picture of their holder, enabling the verifier to compare it with the person presenting them in person. This comparison can be performed manually, or potentially using facial recognition technologies.
While the ISO/IEC 18013-5:2021 standard explicitly requires a portrait picture as part of a valid mDL certificate, our current issuance and verification capabilities do not enforce it. That is because Mobile Credentials were built to meet wider use cases, some of which may not require a portrait picture.
Offline verification
Mobile Credentials need to be verifiable in all areas including where there is poor internet coverage. In our example, the officer needs to be able to verify Emma's licence even if she is pulled over in a location with no internet coverage.
Mobile Credentials are constructed in a way that enables real time offline verification, with no reliance on internet-based technologies. Emma presents a QR code from her digital wallet to initiate a secure BLE connection with the verifier, and have all the information required to complete a verification workflow using non-internet technologies and communication protocols.
When Emma presents the QR code to the police officer, he can scan it to begin a verification workflow and ensure Emma's driving license is verified and valid, regardless of their location and internet coverage.
Refer to the Structure to function and Communication protocols sub-sections for more information.
Selective disclosure
After being cleared by the police officer, Emma pulls over at a local convenience store. Attempting to purchase some age-restricted items, Emma is asked by the retailer to prove her age eligibility. The retailer is a verifier in this digital trust ecosystem.
Emma does not wish to present all the information from her mDL (e.g. residential address or date of birth). Mobile Credentials enable holders to present only specific parts of their credentials to verifiers, based on the content of the request. This is referred to as selective disclosure.
The retailer sends a verification request to Emma's mobile device, to which Emma replies via her digital wallet by only consenting to disclose the required age eligibility proof. The verifier will get the complete signed credential, but only the elements that Emma agreed to disclose will be revealed.
Refer to the Structure to function sub-section for more information on how Mobile Credentials enable this capability, or to Selective disclosure to learn more about the privacy challenges that require this capability.
Session encryption
While Emma is completing the age eligibility verification, other people are waiting in line behind her. Since Emma's and the retailer’s devices communicate over BLE, this data exchange is highly insecure. This puts Emma's personal information at risk of being picked up by potential eavesdroppers that may try and take advantage of it for their own needs.
To enable end-to-end session encryption, Mobile Credentials communication protocols establish session-based encryption/decryption keys to secure the transaction and ensure the Mobile Credentials remain confidential from any possible eavesdroppers.
Refer to the Communication protocols sub-section for more information.
What’s next?
You should now have a good understanding of the core capabilities available for Mobile Credentials. We will now review the different standards and technologies that define and enable these capabilities.