Confidential, Web-based PDF Signing Approvals for Remote Signing Solutions

The transition from token-based key storage to remote signing solutions offers significant flexibility but introduces distinct challenges regarding key usage control and the integrity of the document signing approval process. Specifically, enforcing the What-You-See-Is-What-You-Sign (WYSIWYS) principle is difficult when signatories or their organizations require document confidentiality, yet Trust Service Providers (TSPs) must independently verify signing intent. In this work, we propose a comprehensive blueprint for web-based signing approvals. Our security architecture creates a chain of trust that enables TSPs to enforce the WYSIWYS principle without direct access to signed documents and that is tailored to authentication methods with bandwidth-restricted channels. Our contributions include a novel equivalency attestation mechanism that proves the link between the inputs and outputs of PDF document augmentation procedures required for enveloped signing.