While the use of IC cards with LSI (large-scale integration) is spreading rapidly among credit cards and electronic money associated with transport, ensuring the safety and security of information contained in them is becoming an issue.

Random circuits are integrated as a countermeasure against side channel attacks that are based on information gained from physical implementation of cryptosystems. However, there are no countermeasures against attacks that exploit the vulnerabilities of scan path designs, which are implemented as technology to observe and control LSI in detecting manufacturing defects and sorting out good quality products. There is a potential for this to develop into a new problem in information security.

In the scan path design, “scan registers” are incorporated randomly into the LSI, so it was originally secret information that only the designer knew.

We demonstrated that it is possible to decipher the cryptographic processing of LSI in IC cards by making use of the regularity of the outputted data order due to the fact that the relative positions of FFs (flip-flops) used in a scan chain remain unchanged despite them being connected randomly. As a result of this, we have succeeded in deciphering typical encryption standards that were thought to be impossible to crack, including the AES, RSA cryptosystem, and elliptic curve cryptography (ECC).