Study On The Technique To Extract PUF Information By Scan Chain And Its Application

With the increasing complexity of integrated circuit(IC),more and more money and design effort are invested in the IC design.The risk of illegal copy and distribution of ICs is growing.Therefore,the mechanism of ‘lock and key' is usually presented to protect the security of electronic chips.Only when the input user key is correct,can the design work normally.However,two concerns on the key are created.One is how to guarantee the security of a stored correct key.Secret correct keys traditionally are stored in a non-volatile memory(NVM)which might be easily accessed by some physical attacks.Secure storage of a correct key is a problem to be solved.Some work hence proposed to implement the correct key by hardware design.If a unique key is assigned to each chip,then each design even with same function will correspond to different hardware implementation.This just results in unreasonably high cost in taping out and make the scenario of ‘one chip,one key' impossible.Thus,the same designs must share one key.Under this scenario,if the key of one chip is coincidently cracked,all other designs with the same golden key is not secure any more.To address these concerns,physical unclonable function(PUF)as a potent security primitive was proposed.The unexpected and unclonable PUF information usually serves as a unique ID or secret key in various application scenarios.How to retrieve the PUF information securely at a reasonably low cost is then a concern.A new scheme to extract the PUF information by scan chain was first proposed.PUF information is used to monitor the test control port(tc)of some specific scan cells at certain time.The output response under a designer-specific test vector is hence obfuscated.The difference between the obfuscated output and the normal output can be used to deduce the PUF information.By reusing the existing scan chain design,the design for PUF extraction cannot be removed easily and it incurs negligibly low overhead.As the specific test vector and related design detail are both unknown to others except designer,the probability for an attacker to figure out the PUF information is sufficiently low.This scheme to extract PUF information can be applied in secure scan design or other security-sensitive scenarios.This work then applies the scheme of extracting PUF information to the security scan design.A new secure scan design scheme with PUF-based key for authentication was also proposed.PUF is assigned in different chips as a test key.Secure extraction of PUF information will effectively protect sensitive information in the encryption chip.In this scheme,the PUF's response is invoked only once and hardened into a one-time programmable switch(OTPS).The PUF response required by the designer to derive a test key of each crypto chip can only be recovered at the time of locking the scan chains without directly reading it out.The manufacturer can test the chip normally with no test time penalty before the passed chips are locked.The proposed solution is analyzed to be secure against all known scan-based side-channel attacks and the overhead incurred for the added security is negligibly small.