One-Time Certificates for Reliable and Secure Document Signing

TL;DR

Problem: PKI revocation and private key management hinder usability and scalable adoption for end users. Approach: introduce One-Time Certificates that bind a certificate to a single document, require on-demand (or pre-generated) key pairs, and discard private keys after signing. Contributions: formal OTC framework with a document-binding extension, compatibility with X.509/RFC 5280, forward-security and unforgeability properties, and performance analysis comparing OTC variants to legacy policies. Impact: simplifies private key management, removes end-user revocation, reduces verification overhead, and enables inclusive digital signing at scale, with directions for misissuance detection and quantum-safe upgrades.

Abstract

Electronic documents are signed using private keys and verified using the corresponding digital certificates through the well-known public key infrastructure model. Private keys must be kept in a safe container so they can be reused. This makes private key management a critical component of public key infrastructures with no failproof answer. Therefore, existing solutions must employ cumbersome and often expensive revocation methods to handle private key compromises. We propose a new cryptographic key management model built with long-term, irrevocable digital certificates, each bound to a single document. Our model issues a unique digital certificate for each new document to be signed. We demonstrate that private keys associated with these certificates should be deleted after each signature, eliminating the need to store those keys. Furthermore, we show that these certificates do not require any revocation mechanism to be trusted. We analyze the overhead caused by the frequent generation of new key pairs for each document, provide a security overview and show the advantages over the traditional model.

Figures (3)

• Figure 1: The various time references for a digital certificate.
• Figure 2: Ordered steps to create a digitally signed document using the OTC model. We assume that a key pair has been previously generated by the signer. In step 1, the public key is sent by the signer to the CA. In step [fill color=purple, outer color=white]2, the signer computes the hash of the original document and sends it to the CA. In step 3, the CA issues an OTC with fresh attributes to the signer. In step 4, the signer appends their OTC to the original document. In step 5, the signer computes the hash $\mathsf{h}$ of the tuple $(\mathsf{d}, \mathsf{c})$. In step 6, the signer signs $\mathsf{h}$ with their algorithm of choice. In step 7, the signature is appended to the document, creating the final artifact $(\mathsf{d}, \mathsf{c}, \sigma)$ in orange.
• Figure 3: Time references for an OTC.

Theorems & Definitions (8)

• Definition 1
• Proposition 1
• proof
• Definition 2: bellare1999forward
• Proposition 2
• proof
• Proposition 3
• proof