I'm developing a device where I need to store a symmetric key that the customer uploads to the device. The device is offline at all times, so centralized storage in HSM is not an option. The device does not have a key-pad. The key is used for data encryption/decryption when the device is active. The key cannot be stored in clear text in flash.
I'm just learning about cryptography, so bare with me :) My thinking is that I need to key-wrap the symmetric key to securely store it in flash and unwrap to RAM when in use. To have a secure key to key-wrap with, my thinking is to use a TPM 2.0 chip, like this one, on the device.
My questions are:
- What would a common approach to this issue be?
- If my approach is feasible, how secure is it exactly? What would prevent an attacker from soldering of the TPM chip and use it to unwrap the symmetric key?