A malicious party may attempt to avoid a mobile network operator (MNO) contract involved with subsidy-lock by inserting an interfering piece of hardware called a proxy SIM in a device. The device provided herein uses an authentication technique to guard against a proxy-SIM attack. The device includes a secure element (SE) with subscriber identity module (SIM) functionality present on the SE. The device sends the SE a nonce to be signed over. The SE signs using a public key infrastructure (PKI) private key of the SE and provides a response. The device evaluates whether the response contains a valid signature. If the validation is successful, the device relies on SIM data provided in the response to continue with activation of the device, so that the device can provide services under the MNO contract. If the validation fails, the device will not attempt to access network services with the SIM functionality.