Dynamic scan obfuscation for integrated circuit protections
An integrated circuit (IC) protection circuit can include a reconfigurable block that receives a seed value from a tamper-proof memory and generates a dynamic key; an authentication block that receives the dynamic key from the reconfigurable block and taint bits from a scan chain to generate an authentication signature; and an encryptor that encrypts a test pattern response on the scan chain if a mismatch is found between the authentication signature and a test pattern embedded signature.
1. An integrated circuit (IC) protection circuit, comprising:
a reconfigurable block that receives a seed value from a tamper-proof memory and generates a dynamic key;
an authentication block that receives the dynamic key from the reconfigurable block and taint bits from a scan chain to generate an authentication signature, wherein the authentication block is a block cipher implemented by a substitution permutation (SP) network, and wherein the authentication block comprises:
a first permutation layer coupled to receive the taint bits and a first dynamic key from the reconfigurable block;
a first key-whitening layer coupled to receive outputs of the first permutation layer and a second dynamic key from the reconfigurable block;
a non-linear diffusion layer coupled to receive outputs of the first key-whitening layer;
a second permutation layer coupled to receive outputs of the non-linear diffusion layer and a third dynamic key from the reconfigurable block; and
a second key-whitening layer coupled to receive outputs of the second permutation layer and a fourth dynamic key from the reconfigurable block, the second key-whitening layer outputting the authentication signature;
an encryptor that encrypts a test pattern response on the scan chain if a mismatch is found between the authentication signature and a test pattern embedded signature; and
a comparator coupled to receive the authentication signature from the authentication block and the test pattern embedded signature from the scan chain and output a signal to the encryptor the signal indicating whether or not there is the mismatch between the authentication signature and the test pattern embedded signature.
2. The IC protection circuit of claim 1 , further comprising:
one or more multiplexors (MUXs) coupled to the scan chain to select bits corresponding to the test pattern embedded signature and output the test pattern embedded signature to the comparator.
3. The IC protection circuit of claim 2 , wherein the bits corresponding to the test pattern embedded signature are located at don't care bit locations of a test pattern.
4. The IC protection circuit of claim 1 , wherein the comparator comprises an XOR comparator.
5. The IC protection circuit of claim 1 , wherein the encryptor comprises:
a first XOR coupled to receive the dynamic key from the reconfigurable block and the authentication signature from the authentication block as inputs;
a first OR coupled to receive output from the first XOR and output of the comparator as inputs; and
a first flip-flop coupled to receive output of the first OR as input and output an encryption key according to a scan enable signal.
6. The IC protection circuit of claim 1 , wherein the encryptor receives a second set of dynamic keys from the reconfigurable block for performing encryption.
7. The IC protection circuit of claim 1 , wherein the reconfigurable block comprises:
one or more linear shift feedback registers (LFSRs).
8. The IC protection circuit of claim 1 , further comprising:
a first XOR coupled to receive the first dynamic key and the third dynamic key as inputs; and
a second XOR coupled to receive an output of the first XOR and the authentication signature to output an encryption key,
wherein the encryptor is coupled to receive the encryption key output from the second XOR.
9. The IC protection circuit of claim 1 , wherein the taint bits are located at fixed bit locations in a test pattern loaded onto the scan chain.
10. The IC protection circuit of claim 1 , wherein a number of the test pattern embedded signature bits is equal to or less than a number of don't care bits in a test pattern.
11. An integrated circuit (IC) protection circuit, comprising:
a reconfigurable block that receives a seed value from a tamper-proof memory and generates a dynamic key;
an authentication block that receives the dynamic key from the reconfigurable block and taint bits from a scan chain to generate an authentication signature;
an encryptor that encrypts a test pattern response on the scan chain if a mismatch is found between the authentication signature and a test pattern embedded signature; and
a comparator coupled to receive the authentication signature from the authentication block and the test pattern embedded signature from the scan chain and output a signal to the encryptor the signal indicating whether or not there is the mismatch between the authentication signature and the test pattern embedded signature,
wherein the taint bits are selected for a test pattern on the scan chain to have an equal probability of a one or a zero occurring at a particular bit location, wherein the taint bits are selected to have the equal probability by evaluating, for each scan cell location, Δl=|a l −b l | and μ l =(a l +b l )/2 to determine the scan cell locations with the highest μ l and lowest Δl, where a l is a number of 0's occurring at that scan cell location across all test patterns and b l is a number of 1's occurring at that scan cell location across all test patterns.
12. The IC protection circuit of claim 11 , wherein bit locations for the test pattern are determined after allocation of test pattern embedded signature bits in the test pattern, wherein a number of taint locations is fixed for all test patterns in a test set and the number of taint locations is larger than a number of the test pattern embedded signature bits.
13. The IC protection circuit of claim 12 , wherein the number of taint locations is six times the number of the test pattern embedded signature bits.
14. The IC protection circuit of claim 11 , further comprising:
one or more multiplexors (MUXs) coupled to the scan chain to select bits corresponding to the test pattern embedded signature and output the test pattern embedded signature to the comparator.
15. The IC protection circuit of claim 14 , wherein the bits corresponding to the test pattern embedded signature are located at don't care bit locations of a test pattern.
16. The IC protection circuit of claim 11 , wherein the comparator comprises an XOR comparator.
17. The IC protection circuit of claim 11 , wherein the encryptor comprises:
a first XOR coupled to receive the dynamic key from the reconfigurable block and the authentication signature from the authentication block as inputs;
a first OR coupled to receive output from the first XOR and output of the comparator as inputs; and
a first flip-flop coupled to receive output of the first OR as input and output an encryption key according to a scan enable signal.
18. The IC protection circuit of claim 11 , wherein the encryptor receives a second set of dynamic keys from the reconfigurable block for performing encryption.
19. The IC protection circuit of claim 11 , wherein the reconfigurable block comprises:
one or more linear shift feedback registers (LFSRs).
20. The IC protection circuit of claim 11 , wherein a number of the test pattern embedded signature bits is equal to or less than a number of don't care bits in a test pattern.