Globalized supply chain for electronic circuit manufacturing has reduced the production cost considerably. However, it also presents a challenge since many companies/players contribute to the product and it is not always possible to control or monitor every third-party employee or contractor that takes part in the process. A design house that relies on a foundry for manufacturing needs to ensure that the manufactured devices conform to the agreed-upon process model between the design house and the foundry. Potential deviation from the process model may be due to incidental quality control issues, or due to malicious modifications to the process or circuit layout with the intent of doing harm during in-field operation. In this paper, we present a multivariate methodology to detect even small process and layout level modifications to the circuit by using mission-mode specifications as well as enhanced test modes. We present an algorithm for detecting process/layout modifications and for selection of test inputs to be used in the detection process. Experimental results on an LNA circuit show that the proposed technique can achieve high authentication accuracy even for a single device with a negligible false positive rate.