Tamper resistant counters

A method of persistently storing event counts, the method comprising:

• generating, using a secret cryptographic key, a sequence of numbers arranged in a pseudorandom order, the sequence of numbers indicative of a sequence of addresses of cells in an array of cells, each cell in the array of cells programmable from an initial state to a programmed state to persistently encode data indicative of counter values associated with a particular event;
• comparing addresses of cells having the programmed state with the sequence of addresses to determine whether a tampering event occurred at the array of cells based on an order of addresses in the sequence of addresses,. wherein the tampering event is determined to have not occurred in response to a determination that the addresses of cells having the programmed state correspond to a valid counter value indicated by the sequence of addresses, wherein a first valid counter value corresponding to the sequence of addresses is represented by a first set of programmed cells, wherein a second valid counter value corresponding to the sequence of addresses is represented by a second set of programmed cells, wherein the second set of programmed cells includes the first set of programmed cells and a particular set of cells, and wherein the first set of programmed cells does not include the particular set of cells;
• based on the determination:
• authenticating the array of cells;
• or
• performing a countermeasure;
• and
• responsive to an occurrence of the particular event and authentication of the array of cells as corresponding to the first valid counter value, programming the particular set of cells in the array of cells from the initial state to the programmed state, wherein the particular set of cells is identified based on the order of addresses in the sequence of addresses.

A device for persistently storing event counts, the device comprising:

• an array of cells, each cell in the array of cells configured to be programmed from an initial state to a programmed state to persistently encode data indicative of counter values associated with a particular event;
• means for generating, using a secret cryptographic key, a sequence of numbers arranged in a pseudorandom order, the sequence of numbers indicative of a sequence of addresses of cells in the array of cells;
• means for comparing addresses of cells having the programmed state with the sequence of addresses to determine whether a tampering event occurred at the array of cells based on an order of addresses in the sequence of addresses, wherein the tampering event is determined to have not occurred in response to a determination that the addresses of cells having the programmed state correspond to a valid memory value indicated by the sequence of addresses, wherein a first valid memory value corresponding to the sequence of addresses is represented by a first set of programmed cells, wherein a second valid memory value corresponding to the sequence of addresses is represented by a second set of programmed cells, wherein the second set of programmed cells includes the first set of programmed cells and a particular set of cells, and wherein the first set of programmed cells does not include the particular set of cells;
• means for authenticating the array of cells based on the determination;
• means for performing a countermeasure based on the determination;
• and
• means for programming, responsive to an occurrence of the particular event and authentication of the array of cells as corresponding to the first valid memory value, the particular set of cells in the array of cells from the initial state to the programmed state, wherein the particular set of cells is identified based on the order of addresses in the sequence of addresses.