Hybrid Cost-Effective Decapsulation of Chips for Successful Laser Fault Injection

Abstract

As attacking techniques evolve, hardware security has become increasingly critical. This paper presents a hybrid decapsulation technique combining mechanical and chemical etching to prepare chips for laser fault injection (LFI). We propose a two-stage process: initial mechanical etching using a milling machine to precisely thin the chip down to a 100 micron layer above the die surface, followed by repetitive chemical etching with fuming nitric acid to expose the die while protecting wire bonds. The method is validated through functional tests and an actual LFI attack targeting the AES encryption algorithm on ATmega328P chips. The functional test confirms the accurate operation of the chip after the decapsulation, while the executed LFI attacks successfully modify the ciphertext output, demonstrating the effectiveness of the hybrid decapsulation in transforming chips into suitable candidates for LFI attacks.