CAdES · CMS Advanced Electronic Signature
The format-agnostic signature — wraps anything.
What it is
ETSI's profile for cryptographic signatures over arbitrary bytes (Cryptographic Message Syntax, RFC 5652). CAdES is what's inside PAdES — when you crack open a PAdES-signed PDF, you find a CAdES blob inside. As a standalone format it's used for signing files that aren't PDFs or XML.
Scope
Email (S/MIME is CAdES under the hood), file-archive signing, software distribution, government signing of binary artefacts. Less directly user-facing than PAdES, more often a building block.
What letssign.now does
Every PAdES envelope we produce contains a CAdES signature internally. Standalone CAdES files (.p7m, .p7s) are accepted by /verify, routed through the EU DSS for validation.
Deeper detail
Relationship to PAdES and XAdESExpandClose
PAdES is CAdES embedded in a PDF. XAdES is CAdES's conceptual sibling for XML. Same four conformance levels, same long-term validation model.
Related standards
The frameworks above interlock. Each linked page covers one in full.
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