Case Study: PQC Migration for Android Strongbox Keymaster on Samsung Galaxy Mobile Devices

Advances in quantum computers and their algorithms are significantly changing modern cyber-security systems. Post-Quantum Cryptography (PQC) has been standardized to protect modern security systems from large-scale and reliable quantum computing. However, most PQC algorithms require processing tens to hundreds of times larger key lengths than classical cryptographic algorithms. For example, the RSA-4096 algorithm has a private key of 512 bytes, and the NIST P-521 curve-based ECDSA algorithm has a private key of approximately 66 bytes. However, the FIPS 204 standard PQC digital signature algorithm, ML-DSA-87, has a private key length of 4,896 bytes. This large key length is a heavy burden for Strongbox Keymaster, one of the fundamental modules of the Android security system. This is because the Secure Execution Environment (SEE) in which Android Strongbox Keymaster operates is severely resource-constrained. Therefore, we propose a novel scheme by analyzing the characteristics of modern Android security environments and designing PQC scenarios. Our scheme preserves the hardware-backed security level of Android devices and introduces a new key slotting mechanism to improve the PQC ML-DSA performance of eSE. Through this, in an experimental environment based on real Android devices, our scheme speeds up the PQC ML-DSA-65 signing performance of Strongbox Keymaster by 597 ms (1,826→1,229 ms, about 33%) compared to the drop-in replacement scheme.