Algorithmic Obfuscation for LDPC Decoders

In order to protect intellectual properties against untrusted foundry, many logic-locking schemes have been developed. The idea of logic locking is to insert a key-controlled block into the circuit to make the circuit function incorrectly or go through redundant states without right keys. However, in the case that the algorithm implemented by the circuit is self-correcting, existing logic-locking schemes do not affect the system performance much even if a wrong key is used and hence do not effectively protect the circuit. One example is low-density parity-check (LDPC) error-correcting decoders, which are used in numerous digital communication and storage systems. This article proposes two algorithmic-level obfuscation methods for LDPC decoders. By modifying the decoding process and locking the stopping criterion, our new designs substantially degrade the decoder throughput and/or error-correcting performance, and make the decoder unusable when a wrong key is applied. For an example of the LDPC decoder, our proposed methods reduce the throughput to less than 1/3 and/or increase the decoder error rate by at least two orders of magnitude with at most 0.55% area overhead. Besides, our designs are also resistant to the SAT, AppSAT, and removal attacks.