TPM-FAIL: TPM meets Timing and Lattice Attacks

TL;DR

This paper uncovers timing side-channel vulnerabilities in TPM 2.0 devices, enabling private key recovery through lattice attacks, and demonstrates practical remote exploits affecting real-world VPN systems.

Contribution

It reveals secret-dependent timing leaks in TPM 2.0 devices and demonstrates practical key recovery and remote attacks, highlighting implementation flaws in supposedly secure hardware.

Findings

Timing leakage enables private key recovery via lattice attacks

Successful key extraction from both firmware-based and hardware TPMs

Remote attack on VPN using TPM signatures to recover server keys

Abstract

Trusted Platform Module (TPM) serves as a hardware-based root of trust that protects cryptographic keys from privileged system and physical adversaries. In this work, we perform a black-box timing analysis of TPM 2.0 devices deployed on commodity computers. Our analysis reveals that some of these devices feature secret-dependent execution times during signature generation based on elliptic curves. In particular, we discovered timing leakage on an Intel firmware-based TPM as well as a hardware TPM. We show how this information allows an attacker to apply lattice techniques to recover 256-bit private keys for ECDSA and ECSchnorr signatures. On Intel fTPM, our key recovery succeeds after about 1,300 observations and in less than two minutes. Similarly, we extract the private ECDSA key from a hardware TPM manufactured by STMicroelectronics, which is certified at Common Criteria (CC) EAL 4+, after fewer than 40,000 observations. We further highlight the impact of these vulnerabilities by demonstrating a remote attack against a StrongSwan IPsec VPN that uses a TPM to generate the digital signatures for authentication. In this attack, the remote client recovers the server's private authentication key by timing only 45,000 authentication handshakes via a network connection. The vulnerabilities we have uncovered emphasize the difficulty of correctly implementing known constant-time techniques, and show the importance of evolutionary testing and transparent evaluation of cryptographic implementations. Even certified devices that claim resistance against attacks require additional scrutiny by the community and industry, as we learn more about these attacks.