CAdES is a new standard for advanced digital signature. It was introduced by the European Directive on a community framework for Electronic Signatures, which extends the previous standard, CMS, specifying several additional profiles. The reason for this was the lack in CMS of some important features of extended electronic signature, the most obvious of which is long term validation, that means the ability to prove signature validity after a long period, several years or even decades after it was created.
CAdES specifies additional forms, or profiles, which describe the structure of advanced electronic signature. These profiles are CAdES-T, CAdES-C, CAdES-X-L and CAdES-A. Each following profile adds some properties to the previous one.
What's New in CAdES
The philosophy of CAdES includes the concept of signature policies that can be used to establish technical consistency when validating electronic signatures.
When the signature policy used by the verifier is either explicitly indicated by the signer or is obvious due to the nature of the data being signed, consistent result can be obtained while validating an electronic signature.
When the signature policy being used by the verifier is neither indicated by the signer nor can be derived from other data, or the signature policy is incomplete, then verifiers, including arbitrators, may obtain different results when validating an electronic signature. Therefore, comprehensive signature policies that ensure consistency of signature validation are recommended from both the signer's and verifier's point of view.
Thus we have two forms of CMS advanced electronic signature specified in the CAdES standard, namely, the CAdES Basic Electronic Signature (CAdES-BES) and the CAdES Explicit Policy-based Electronic Signature (CAdES-EPES). Conformance to the CAdES standard mandates that the signer create one of these formats.