Problem
Teams needed to collect signatures from multiple parties and guarantee that documents were valid years later. The previous process relied on manual signing tools and lacked verifiable certificate chains.
Constraints
The solution had to support multi-signer workflows, timestamping, certificate revocation checks, and strict audit evidence. Documents could not leave approved storage regions.
Architecture
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Signing service with a job queue, certificate authority integration, and a validation pipeline.
The pipeline separated signing from verification. A signing service applied signatures and a verification service validated byte ranges, certificate chains, and timestamps. Both emitted events to a centralized audit log.
Key decisions & trade-offs
We implemented incremental PDF updates to preserve prior signatures, accepting a more complex verification step in return for long-term validity. Certificate handling was isolated in a single service to reduce the risk surface.
Security & compliance
Keys were stored in HSM-backed vaults, and every signature request required explicit approval and scoped permissions. Validation results were immutable and stored alongside the document history.
Outcome
The system produced verifiable, long-lived signatures with clear audit artifacts for regulators and clients.
What I’d improve next
Add automated certificate renewal simulations to detect expiring chains before they impact production documents.