Scan chain encryption for the test, diagnosis and debug of secure circuits

Abstract

Scan attacks exploit facilities offered by scan chains to retrieve embedded secret data, in particular secret keys used in crypto-processors for encoding information in such a way that only knowledge of the secret key allows to access it. This paper presents a scan attack countermeasure based on the encryption of the scan chain content. The goal is to counteract the security threats and, at the same time, to preserve test efficiency, diagnosis and debugging abilities. We propose to use the secret-key management policy embedded in the device under test in order to encrypt both control and observed data at test time. This solution does not require additional key management, provides same test/diagnostic and debug facilities as under classical scan design with marginal impacts on area and test time.

Defense-in-depth: A recipe for logic locking to prevail

“…DIPs rule out incorrect keys utilizing the output corruptibility of the miter circuit constructed using locked design and activated design. For sequential designs, it is assumed that an IC's internal states can be accessed and controlled via scan chains to [59] Internal States Scan encryption [45], DOS [51] Resetting Attack [46] Internal Secrets LCSS [48], DOS [51], Lock & Key [60], Scan encryption [45] Flushing Attack [47] Bit-role Identification Combinational Function Recovery [54] Functionality DOS [51] SAT Attack [4] Obfuscation Key…”

“…Scan Encryption: A countermeasure against scan-based side channel attacks could be done through the encryption of the scan chain content [45]. These attacks use an efficient and secure block cipher placed at each scan port to decrypt/encrypt scan patterns/responses at each scan input/output, respectively.…”

Experimentations on scan chain encryption with PRESENT

“…The countermeasure proposed in [9] targets circuits embedding at least one crypto-core. We assume a tamperresistant memory to store secret-keys and a key management policy (no additional key management policy is required).…”

“…The countermeasure described in [9] consists in using light block ciphers for scan encryption. Assuming a cryptoprocessor embedded with key management and storing, the same key storage present in the circuit under test is used to store the scan chain encryption key.…”

“…This paper intends to evaluate costs involved by the solution proposed in [9] on several circuits examples. Two variants of the original scheme are evaluated showing that test time overhead due to scan chain encryption can be largely offset with low cost extra DfT.…”