Signing is most powerful when it disappears into the application. Rather than sending users to a separate portal, a signature API lets you embed advanced and qualified signing directly into your own software — issuing, signing and verifying documents as part of your workflow. For developers, the question is which signing operations you need and which standards to build on.
Document signing versus hash signing
There are two main ways to call a signing service. In document signing, you send the document (or its prepared form) and receive it back signed, with the signature embedded — convenient for PDFs and PAdES output. In hash signing, only the cryptographic hash of the document leaves your environment; the service signs the hash and returns the signature, which you embed locally. Hash signing is ideal when documents must never leave your premises for confidentiality or data-residency reasons.
Build on open standards
The interoperable foundation for remote signing APIs is the Cloud Signature Consortium (CSC) API, standardised as ETSI TS 119 432. It defines REST-style, JSON-over-HTTP operations for creating advanced and qualified signatures and seals in the cloud, aligned to eIDAS. Building on this standard means your integration is portable and not locked to a single proprietary interface.
What you can do through the API
- Create AES and QES for documents on behalf of verified signers.
- Apply electronic seals for automated, organisation-level signing at volume.
- Add timestamps and PAdES long-term validation so signatures stay verifiable for years.
- Verify signatures programmatically as part of your processing.
Integration and security considerations
A clean integration handles authentication of both the application and the signer, enforces sole control for qualified signatures, and manages credentials securely. Look for clear documentation, sandbox access for testing, and support for both synchronous and high-volume batch operations. Done well, signing becomes one reliable API call inside a workflow your users never have to leave.
Embed signing where your users already work.
primesign APIs deliver document and hash signing for AES, QES and seals over the standards-based CSC interface. Talk to our team about integrating signing into your application.
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