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

What is this patent about?

’223 is related to the field of secure machine-to-machine (M2M) communications and the remote management of cellular credentials. Specifically, it addresses the technical challenges of securely provisioning and updating network access credentials, such as the shared secret key K, within an embedded universal integrated circuit card (eUICC) without requiring physical SIM card swaps or relying on insecure electronic distribution channels.

The underlying idea behind ’223 is to enable a wireless module to internally derive its own cryptographic keys and network credentials rather than receiving them in plaintext or simple encrypted files. By utilizing a key derivation function (KDF) and shared secret algorithms that incorporate unique hardware component parameters and dynamic tokens, the module and a subscription manager can mutually arrive at the same secret keys. This ensures that sensitive data like the network key K is never actually transmitted over the air, even in encrypted form, thereby eliminating a major point of vulnerability.

The claims of ’223 focus on a multi-stage derivation process where a module uses an eUICC to establish secure communication with a subscription manager. The process involves authenticating the manager using a network public key, receiving a token, and deriving a module-specific PKI key pair. These elements are then fed into a KDF to produce a first shared secret, which subsequently acts as a high-entropy input for a shared secret algorithm (utilizing a secure hash) to derive a second shared secret key. This final key is specifically used by the eUICC to decrypt a downloaded profile containing new network access credentials.

In practice, the invention allows a module to bootstrap its security using an initial, potentially low-security profile or a protected hardware identity to authenticate with a subscription manager. Once authenticated, the module generates a derived module private key and uses it to participate in a secure handshake. This handshake results in a mutually derived shared secret that is unique to that specific piece of hardware and the current session. The module then uses this secret to unlock a second, more permanent eUICC profile that contains the actual IMSI and key K needed for full cellular service.

This approach differs from prior solutions by moving the point of credential generation from the server to the device itself. Traditional eUICC provisioning relies on the server encrypting a pre-generated key K and sending it to the module, which leaves the key vulnerable to any compromise in the transport-layer encryption. By contrast, ’223 ensures the secret shared network key K is derived locally within the secure environment of the eUICC, maintaining full compatibility with legacy LTE and 3GPP infrastructure while significantly hardening the provisioning process against interception.