Removing Signing Keys for Certificate Authorities via Physically Unclonable Functions to Enhance Public Key Infrastructure Security

Core Concepts

Armored Core proposes removing the private signing keys of Certificate Authorities and replacing them with Physically Unclonable Function-based operations to establish physically trusted binding of certificates, thereby eliminating the risk of signing key exposure.

Abstract

The paper presents Armored Core, a novel design for enhancing the security of Public Key Infrastructure (PKI) by removing the private signing keys of Certificate Authorities (CAs) and replacing them with Physically Unclonable Function (PUF)-based operations.
Key highlights:

The exposure of CA's private signing keys is a critical security issue in PKI, as it allows attackers to generate fraudulent certificates. Existing mitigations, such as hardware security modules and trusted execution environments, have proven ineffective against targeted attacks.
Armored Core proposes using PUF to establish physically trusted binding of certificates, eliminating the need for a digital signing key. CAs issue PUF-based X.509v3 certificates, where the endorsement of domain public keys is done using PUF responses instead of cryptographic signatures.
Armored Core introduces a PUF transparency logging mechanism, built upon Certificate Transparency, to record the PUF invocation behaviors of CAs, enabling monitoring and auditing of PUF usage.
The authors provide a formal cryptographic proof of Armored Core's main functions and implement a prototype on real-world PKI codebases, demonstrating its effectiveness and efficiency. The integration of Armored Core improves computing efficiency by over 4.9% and reduces certificate storage by more than 20%.
Armored Core addresses the key design challenges of non-queryable PUF for CAs, pre-storage of CRPs on clients, and hardware-bound CA functions, enabling seamless integration with existing PKI systems.

Stats

The paper states that Armored Core can improve computing efficiency by over 4.9% and reduce certificate storage by more than 20% compared to traditional PKI systems.

Quotes

"As many real-life incidents and CVEs have shown, the exposure risk of private signing keys of CA continues to persist. Even today, various vulnerabilities can lead to the direct or indirect exposure of these crucial keys."
"The existing mitigations are difficult to eliminate the risk of signing key exposure. Attackers can employ targeted exploitation to bypass the defenses. One successful exploitation is enough for them to issue numerous fraudulent certificates."

Key Insights Distilled From

Armored Core of PKI: Remove Signing Keys for CA via Physically Unclonable Function

by Xiaolin Zhan... at arxiv.org 04-25-2024

https://arxiv.org/pdf/2404.15582.pdf

Deeper Inquiries

How can Armored Core be extended to support other PKI operations beyond certificate issuance, such as revocation and renewal?

Armored Core can be extended to support other PKI operations by incorporating PUF-based mechanisms for revocation and renewal processes. For revocation, the CA can use PUF responses to sign revocation messages, ensuring the integrity and authenticity of the revocation process. This can add an extra layer of security to the revocation mechanism, making it more resistant to attacks. Additionally, for certificate renewal, the CA can utilize PUF responses to endorse the new certificates, providing a physically trusted binding without relying on traditional signing keys. By extending the use of PUF in these operations, Armored Core can enhance the overall security and trustworthiness of the PKI ecosystem.

What are the potential challenges and limitations in deploying Armored Core in large-scale, real-world PKI environments?

Deploying Armored Core in large-scale, real-world PKI environments may pose several challenges and limitations. Some of these include:

Hardware Integration: Implementing PUF-based solutions may require significant hardware modifications and upgrades in existing PKI systems, which can be costly and time-consuming.

Compatibility Issues: Ensuring compatibility with existing PKI infrastructure and protocols may be challenging, especially when integrating PUF technology into legacy systems.

Performance Overhead: The incorporation of PUF mechanisms may introduce additional computational overhead, potentially impacting the performance of CA operations in large-scale environments.

Security Concerns: While PUF offers enhanced security through physically trusted bindings, there may be concerns about the vulnerability of PUF instances to physical attacks or modeling attacks, which could compromise the security of the system.

Scalability: Ensuring the scalability of Armored Core in large-scale environments, where numerous certificates are issued and managed, can be a significant challenge. Managing a large pool of PUF instances and coordinating their operations efficiently may require robust infrastructure and management protocols.

Addressing these challenges and limitations will be crucial for the successful deployment of Armored Core in real-world PKI environments.

How can the PUF pooling layer in Armored Core be further optimized to improve the performance and scalability of CA operations?

To optimize the PUF pooling layer in Armored Core for improved performance and scalability of CA operations, the following strategies can be considered:

Dynamic Resource Allocation: Implement dynamic resource allocation algorithms that can efficiently distribute PUF instances based on workload demands. This can help optimize resource utilization and enhance the scalability of CA operations.

Load Balancing: Introduce load balancing mechanisms to evenly distribute PUF instances across multiple CA servers. This can prevent resource bottlenecks and ensure smooth operation during peak loads.

Parallel Processing: Enable parallel processing of PUF instances within the pooling layer to expedite certificate issuance and validation processes. This can improve the overall performance of CA operations.

Fault Tolerance: Implement fault-tolerant mechanisms within the pooling layer to handle failures or disruptions in PUF instances. This can ensure continuous operation and prevent service interruptions.

Monitoring and Optimization: Implement monitoring tools to track the performance of PUF instances and identify potential bottlenecks or inefficiencies. Use this data to continuously optimize the pooling layer for better performance and scalability.

By implementing these optimization strategies, the PUF pooling layer in Armored Core can be enhanced to support large-scale CA operations effectively and efficiently.