US Patent 10044514 Secure external key storage for programmable ICS

The disclosure describes approaches for protecting a circuit design for a programmable integrated circuit (IC). A black key is generated from an input red key by a registration circuit implemented on the programmable IC, and the black key is stored in a memory circuit external to the programmable IC. The programmable IC is configured to implement a pre-configuration circuit, which inputs the black key from the memory circuit and generates the red key from the black key. A ciphertext circuit design is decrypted into a plaintext circuit design by the programmable IC using the red key, and the red key is erased from the programmable IC. The programmable IC is reconfigured with the plaintext circuit design.