Key derivation for a module using an embedded universal integrated circuit card

What is this patent about?

’206 is related to the field of secure machine-to-machine (M2M) communications and the remote management of network credentials. Specifically, it addresses the technical challenges of securely provisioning an embedded universal integrated circuit card (eUICC) with a profile containing network access credentials without relying on the physical distribution of SIM cards or the insecure electronic transmission of pre-shared secret keys.

The underlying idea behind ’206 is to leverage public key infrastructure (PKI) and elliptic curve cryptography to mutually derive a shared secret key between a module and a subscription manager. Instead of transmitting a sensitive network key over the air, the system uses an Elliptic Curve Diffie-Hellman (ECDH) exchange to establish a secure session key. This derived key is then used to encrypt the entire eUICC profile, ensuring that only the specific hardware module possessing the corresponding private key can access the network credentials.

The claims of ’206 focus on a method for a subscription manager to securely distribute a profile by utilizing a combination of asymmetric and symmetric cryptography. The process involves receiving a module's certificate from a provider, responding to a hardware challenge with an elliptic curve digital signature, and generating a temporary network key pair. The subscription manager then derives a shared secret using the module's public key and its own network private key, which serves as the encryption key for an AES-128 encrypted payload containing the network access credentials.

In practice, the module and the subscription manager system interact to verify each other's identities before any sensitive data is exchanged. The subscription manager uses its server private key to sign the challenge received from the module, providing authoritative proof of its identity. Once mutual trust is established, the ECDH protocol allows both parties to arrive at the same mutually derived shared key independently. This eliminates the risk of a 'man-in-the-middle' intercepting the raw network key K during the provisioning process.

This approach differs from prior methods that relied on pre-shared keys (PSKs) burned into physical SIM cards at the factory or encrypted files protected by static passwords. By using dynamic key derivation and hardware-specific certificates, the invention allows modules to be hermetically sealed and deployed globally while retaining the ability to securely switch between different mobile network operators. This provides a scalable architecture for the Internet of Things where physical access to devices is often impossible or cost-prohibitive.