This paper describes BlockPKI, a blockchain-based public-key infrastructure that enables an automated, resilient, and transparent issuance of digital certificates. Our goal is to address several shortcomings of the current TLS infrastructure and its proposed extensions. In particular, we aim at reducing the power of individual certification authorities and make their actions publicly visible and accountable, without introducing yet another trusted third party. To demonstrate the benefits and practicality of our system, we present evaluation results and describe our prototype implementation.
As an enhancement to the standard web PKI, Google developed Certificate Transparency (CT) @cite_24 to detect targeted attacks by making all the certificates submitted to their log servers publicly visible. To work effectively, CT requires that every certificate is accompanied by a signed statement that a log has received the certificate (and will add it to its store). Logs in CT must be highly available as they are necessary for issuing certificates. Moreover, CT does not provide any attack prevention as it is designed exclusively for attack detection. AKI @cite_25 and its successor ARPKI @cite_30 rely on certificate logs similar to CT's, but provide additional security guarantees: they employ multi-signature certificates signed by @math CAs, and aim at protecting users from an adversary who would be able to compromise up to @math CAs. These systems rely on log servers whose availability is crucial for standard operations. Moreover, AKI and ARPKI lack an automated framework for requests and payment.
@cite_24 @cite_30 @cite_25
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We present ARPKI, a public-key infrastructure that ensures that certificate-related operations, such as certificate issuance, update, revocation, and validation, are transparent and accountable. ARPKI is the first such infrastructure that systematically takes into account requirements identified by previous research. Moreover, ARPKI is co-designed with a formal model, and we verify its core security property using the Tamarin prover. We present a proof-of-concept implementation providing all features required for deployment. ARPKI efficiently handles the certification process with low overhead and without incurring additional latency to TLS. ARPKI offers extremely strong security guarantees, where compromising n-1 trusted signing and verifying entities is insufficient to launch an impersonation attack. Moreover, it deters misbehavior as all its operations are publicly visible. Recent trends in public-key infrastructure research explore the tradeoff between decreased trust in Certificate Authorities (CAs), resilience against attacks, communication overhead (bandwidth and latency) for setting up an SSL TLS connection, and availability with respect to verifiability of public key information. In this paper, we propose AKI as a new public-key validation infrastructure, to reduce the level of trust in CAs. AKI integrates an architecture for key revocation of all entities (e.g., CAs, domains) with an architecture for accountability of all infrastructure parties through checks-and-balances. AKI efficiently handles common certification operations, and gracefully handles catastrophic events such as domain key loss or compromise. We propose AKI to make progress towards a public-key validation infrastructure with key revocation that reduces trust in any single entity.