Trace Buffer Attack: Security versus observability study in post-silicon debug

Since the standardization of AES/Rijndael symmetric-key cipher by NIST in 2001, it gained widespread acceptance in various protocols and withstood intense scrutiny from the theoretical cryptanalysts. From the physical implementation point of view, however, AES remained vulnerable. Practical attacks on AES via fault injection, differential power analysis, scan-chain and cache-access timing have been demonstrated so far. Along this line, in this paper, we propose a novel and effective attack, termed Trace Buffer Attack. Trace buffers are extensively used for post-silicon debug of digital designs. We identify this as a source of information leakage and show that, unless proper countermeasure is taken, Trace Buffer Attack is capable of partially recovering the secret keys of different AES implementations. We report the detailed process of trace-buffer attack with experimental results. We also propose a countermeasure in order to avoid such attack.