  Additive Manufacturing (AM), a.k.a. 3D Printing, is increasingly used to
manufacture functional parts of safety-critical systems. AM's dependence on
computerization raises the concern that the AM process can be tampered with,
and a part's mechanical properties sabotaged. This can lead to the destruction
of a system employing the sabotaged part, causing loss of life, financial
damage, and reputation loss. To address this threat, we propose a novel
approach for detecting sabotage attacks. Our approach is based on continuous
monitoring of the current delivered to all actuators during the manufacturing
process and detection of deviations from a provable benign process. The
proposed approach has numerous advantages: (i) it is non-invasive in a
time-critical process, (ii) it can be retrofitted in legacy systems, and (iii)
it is airgapped from the computerized components of the AM process, preventing
simultaneous compromise. Evaluation on a desktop 3D Printer detects all attacks
involving a modification of X or Y motor movement, with false positives at 0%.

Cryptography and Security