Ultra-thin glass seals for protection against unauthorized tampering by permanent monitoring of optical integrity parameters

Abstract

The advancement of high technology manipulation tools to gain unauthorized access to security eminent hardware in mobile devices demands more sophisticated tamper protection solutions. We developed sensory seal envelopes of ultra-thin glass with individual optical spectra used as signature for tamper protection of electronic controls or cryptographic communication units. A miniaturized autonomic read-out system detects and analyzes the state of the seal. The read-out system is located in the protected area under the seal, together with the secret, in order to protect against attacks via electronic interfaces, such as the mimicry of signature data and the deceptive simulation of the seal's integrity. We introduced a single optical waveguide Bragg grating element via femtosecond laser processing into ultra-thin glass slides. This single Bragg grating combines different functions: It is a sensor element which diffracts the light out-of-plane and doing this in a dispersing manner to create a unique spectral signature. This combination allows a miniaturization of the optical analysis of the dispersed light. We demonstrated that a single waveguide Bragg grating element, inscribed into a monolithic ultra-thin glass foil of 10 cm x 10 cm size, is sufficient for the registration of marginal local mechanical forces onto the glass foil, causing vertical deformations of less than 50 µm at any position. In case of manipulation attempts, such as drilling, cutting, and lasing through the glass foil, the seal's monitoring system recognizes the change or complete loss of the individual spectral signature immediately. We present all elements needed for an optical tamper protection system, based on the sensory seal envelopes of ultra-thin glass in a miniaturized setup, thus reflecting the high potential for future commercial solutions.