A Nonlinear Stream Cipher for Encryption of Test Patterns in Streaming Scan Networks

With the biennial doubling of the number of transistors in a given area of silicon, contemporary integrated circuits (IC) are forging more and more often and will continue to forge complex system-on-chip (SoC) designs. Their equally complex manufacturing and in-system tests are now carried out through top-level test data delivery nets that enable fast streaming of test data to, from, and throughout a chip. However, it is essential to apply restrictions mitigating risks associated with unauthorized access and usage of SoCs as well as to protect the test infrastructure against hardware security threats, and thus to prevent leakage of secret information or other sensitive assets while tests are carried out. Existing security IP cores raise concerns related to their complexity in terms of area footprint, performance, power, impact on an SoC integration flow, and testability. This paper presents simple and lightweight, yet effective and scalable, test data stream ciphers (SCs) that can be used to encrypt and decrypt test data employed in tests of SoCs and delivered via Streaming Scan Network (SSN) – a new packetized test data network. A single cipher is comprised of three Galois nonlinear feedback shift registers working in tandem to yield a large number of parallel, cryptographically secure pseudorandom keystreams. A comprehensive evaluation, including NIST statistical test suits, show high efficiency of the proposed ciphers, and is reported herein.