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Ring Oscillator PUF does not generete unique ID for each FPGA

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kahlenberg

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Hi,

I am designing a Physically Uncolonable Function using Ring Oscillator on FPGA (Spartan6). However, it does not generate uniqe ID for each chip, it generates exactly same value for different chips. Different ROs must generate different frequency due to die-imperfection. I will compare those frequencies and generate bits, which should be uniqe for each chip, since each chip has different physicall die-imperfection.

First, I generate 16 ROs, each with 51 inverter gates, all of them are connected to two multiplexers, I connected the select inputs of multiplexers with 8-bit dip-switch. Outputs of multiplexers are connected to two 16-bit counters. Outputs of counters are connected to a comparator, If first counter reachs end value (111...11) (if it is faster than second counter) comparator gives '1', if second counter is faster than first, comparator gives a '0'. This generates only one bit. I replicated this design 16-times to generate 16-bit response. The first bits of this response (3 downto 0) are connected to 4-leds. I tested the design with 3 different chips, they give exactly same respnose, which is not desired.
How can I make it in order to have different responses?

Thanks.

ring_oscillator.vhd
Code:
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
use IEEE.NUMERIC_STD.ALL;

-- Uncomment the following library declaration if instantiating
-- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity ring_oscilator is
	generic (delay: time := 200ps;
				chain_len: integer := 16);
    port( rst_i : in  std_logic;
			 ro_o  : out  std_logic);
end ring_oscilator;

architecture Behavioral of ring_oscilator is
  signal chain : std_logic_vector(chain_len downto 0);
  attribute keep: boolean;
  attribute keep of chain: signal is true;
begin

--assert chain_len mod 2 = 1 report "Length of ring must be an odd number!" severity failure;

  gen_chain:
  for i in 1 to chain_len generate
    chain(i) <= not chain(i-1) after delay;
  end generate;
  chain(0) <= chain(chain_len) nor rst_i after delay;

 ro_o <= chain(chain_len);

end Behavioral;

debounce.vhd
Code:
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity debouncer is
  generic(
    counter_size  :  INTEGER := 19); --counter size (19 bits gives 10.5ms with 50MHz clock)
  port(
    clk_i     : in  std_logic;  --input clock
    button_i  : in  std_logic;  --input signal to be debounced
	 enable_i  : in  std_logic;   -- for simulation
    result_o  : out std_logic); --debounced signal
end debouncer;

ARCHITECTURE logic of debouncer is
  signal flipflops   : std_logic_vector(1 downto 0); --input flip flops
  signal counter_set : std_logic;                    --sync reset to zero
  signal counter_out : std_logic_vector(counter_size downto 0) := (others => '0'); --counter output
begin

  counter_set <= flipflops(0) xor flipflops(1);   --determine when to start/reset counter
  
  process(clk_i)
  begin
    if rising_edge(clk_i) then
      flipflops(0) <= button_i;
      flipflops(1) <= flipflops(0);
		
		if enable_i = '1' then
			if(counter_set = '1') then                  --reset counter because input is changing
				counter_out <= (others => '0');
			elsif(counter_out(counter_size) = '0') then --stable input time is not yet met
				counter_out <= counter_out + 1;
				else                                        --stable input time is met
					result_o <= flipflops(1);
				end if;
						else
			result_o <= button_i;
			end if;

		end if;
  end process;
end logic;

top.vhd
Code:
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.std_logic_misc.ALL;
use IEEE.std_logic_unsigned.ALL;
use ieee.numeric_std.all;

entity top is
    Generic (
					nr_ro     : natural := 16;
					puf_width : natural := 16
				);
    Port 	( 	
	 				shift_i   : in  std_logic ; --debug
					dout_o    : out std_logic_vector(3 downto 0); --debug					
					sel_i     : in  std_logic_vector(7 downto 0); --debug	
					clk_i   : in STD_LOGIC;
					rst_i   : in STD_LOGIC--; 
--					puf_out : out STD_LOGIC_VECTOR (puf_width-1 downto 0)
				);
end top;

architecture Behavioral of top is

	constant c_width    : natural := puf_width;
	constant c_number_of_ro : natural := nr_ro;
 
-----------------------------DEBUG-------------------------------------
	signal s_sel     : std_logic_vector(7 downto 0) := (others => '0');
	signal s_dout    : std_logic_vector(3 downto 0) := (others => '0');
	signal s_shift   : std_logic := '0';
   signal s_shift_pre : std_logic := '0';
	signal s_pulse  : std_logic := '0';		
	signal s_msb     : integer range 0 to 16 := 4;
-----------------------------------------------------------------------	

	signal s_reset	   : std_logic := '0';
	signal s_finish   : std_logic_vector (c_width-1 downto 0):= (others => '0');
	signal s_finished : std_logic := '0';
	signal s_puf_out  : std_logic_vector (c_width-1 downto 0):= (others => '0');

--------------components----------------------------
   component puf_bit
		generic (
						nr_ro: natural := c_number_of_ro
					);
		port 		(
					clk_i     : in  std_logic;
					rst_i     : in  std_logic;
					sel1_i    : in  unsigned(3 downto 0);
					sel2_i    : in  unsigned(3 downto 0);
					finish_o	 : out  std_logic;
					puf_bit_o : out  std_logic
					);
   end component;

	component debouncer
	generic(counter_size  :  integer := 19); --counter size (19 bits gives 10.5ms with 50MHz clock)
	port(
    clk_i     : in  std_logic;  --input clock
    button_i  : in std_logic;  --input signal to be debounced
	 enable_i  : in std_logic; 
    result_o  : out  std_logic); --debounced signal
	end component;

begin

Generate_PUF:
	for i in 0 to c_width-1 generate		
		Multiple_Puf_Bits: puf_bit 
			generic map (nr_ro => c_number_of_ro)
			port map (
							clk_i     => clk_i, 
							rst_i     => s_reset, 
							sel1_i    => unsigned(s_sel(3 downto 0)),   
							sel2_i    => unsigned(s_sel(7 downto 4)),
							finish_o	 => s_finish(i),
							puf_bit_o => s_puf_out(i)
			);
		end generate;
		
		reset_debounce: debouncer
		generic map (counter_size => 19)
		port    map (clk_i => clk_i, button_i => not rst_i, enable_i => '1', result_o => s_reset); --On FPGA board btn is low active
	
		btn_debounce: debouncer
		generic map (counter_size => 19)
		port    map (clk_i => clk_i, button_i => not shift_i, enable_i => '1', result_o => s_shift); --On FPGA board btn is low active
	
      s_finished <=  AND_REDUCE(s_finish);
------------ debug--------------------------------
		s_sel   <= sel_i;    
		dout_o  <= s_puf_out(7 downto 4);

----------------------------------------------	


end Behavioral;
 

Expecting radically different results from different die possibly from the same lot code is less likely to produce as much variation as across multiple lots...

Disregarding why you are seeing no variation, why don't you use the device DNA and lock the code to that value for each part. Designs that require anti-cloning usually use the device DNA to make sure the code is only running on the device it was generated to run on. Of course this means the bit file for each device is different.
 

Expecting radically different results from different die possibly from the same lot code is less likely to produce as much variation as across multiple lots...

Disregarding why you are seeing no variation, why don't you use the device DNA and lock the code to that value for each part. Designs that require anti-cloning usually use the device DNA to make sure the code is only running on the device it was generated to run on. Of course this means the bit file for each device is different.

Thanks for reply. I am doing it for a seminar work. I will not use it in a commercial product. Just for research.
 

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