Cloud Signature Consortium API (CSC API)

The Cloud Signature Consortium (CSC) API is the open standard for remote signing integrations, used by QTSPs and EUDI Wallet signing flows.

The Cloud Signature Consortium (CSC) API is an open REST/HTTP standard, maintained by the Cloud Signature Consortium (CSC) - an industry consortium founded in 2016 by Adobe and a group of QTSPs and technology vendors - for integrating remote signing into applications. It defines how a signing application discovers a remote signature service, lists a user's credentials, requests authorisation, and receives the signature. Each credential is a signing key and its certificate held at the QTSP, for either a personal electronic signature or an organisation's electronic seal, so document platforms can integrate any compliant QTSP.

The specification has evolved through several versions; version 2.2 (November 2025) is the current release. Commission Implementing Regulation (EU) 2024/2979 already references CSC API v2.0 for EUDI Wallet remote signing functions, though it is not yet confirmed whether a later version will be referenced in future updates to the eIDAS implementing acts. Cleverbase exposes its signing service through this interface for partners.