XAdES

XAdES stands for XML Advanced Electronic Signatures and is a set of extensions to the XML Digital Signature (XML-DSig) standard defined by the European Telecommunications Standards Institute (ETSI). It provides a framework for adding optional signature properties and data that enable long-term validation of digitally signed XML documents. By embedding information about the signer, the signing policy, revocation data, and timestamps, XAdES makes it possible to verify signatures long after the original signing event.

The core idea of XAdES is to augment a baseline XML signature with qualifying properties. These include details about the signing certificate, the signature policy, and, crucially, data needed for future validation such as OCSP responses and certificate revocation lists. XAdES supports time stamping and the inclusion of complete certificate chains and revocation data to preserve the ability to verify signatures even when certificates or revocation data have expired.

XAdES defines several profiles with increasing levels of assurance and data retention. Common profiles are XAdES-BES (Baseline Electronic Signature), XAdES-EPES (Explicit Policy Electronic Signature), XAdES-T (signature with a trusted timestamp), XAdES-C (with complete revocation data), XAdES-X (including explicit information like OCSP responses and CRLs), XAdES-X-L (long-term), and XAdES-A (archival). These profiles are designed to support long-term validity and archival needs for XML documents.

In practice, XAdES is used for legal and archival signing of XML documents, especially within European contexts where long-term validation and policy clarity are important. It remains compatible with XML-DSig workflows and is supported by various signing toolkits and archival systems, though adoption varies by sector and jurisdiction.