Unchangeable physical unclonable function in non-volatile memory

A method for operating a circuit including a plurality of non-volatile memory cells, comprising:

• executing an authentication protocol;
• after the authentication protocol is successful, executing a physical unclonable function to generate a key;
• storing the key in a set of non-volatile memory cells;
• and
• after storing the key, disabling changes to data stored in the set of non-volatile memory cells.

A circuit, comprising:

• a plurality of non-volatile memory cells characterized by
• logic configured to use a physical unclonable function to produce a key, and to store the key in a set of non-volatile memory cells in the plurality of non-volatile memory cells, wherein the physical unclonable function is configured to utilize entropy generated using non-volatile memory cells in the plurality of non-volatile memory cells to produce the key;
• logic configured to disable changes to data in the set of non-volatile memory cells and to disable use of the physical unclonable function after the key is stored in the set;
• and
• authentication logic requiring a successful authentication protocol to enable the physical unclonable function to produce the key.