What are PAdES, XAdES, CAdES and their subsequent variants?

PAdES is an acronym for PDF Advanced Electronic Signature. It is a technical standard relating to the extension packages and rules that apply when electronically signing PDF documents. The main advantage of some PAdES is that documents can remain valid for a longer period of time even if the actual qualified certificate has expired. It also allows you to validate documents retrospectively when new PDF versions are created, thus ensuring the integrity of your stored documents.

XAdES and CAdES are acronyms for XML and CMS advanced electronic signature. In essence, it is a framework for working with XML and SMC data and electronic signatures so that the origin and owner of the data in those formats can be verified.

Now let's explain the basic breakdown of PAdES documents. According to the European legislation, there are 4 basic levels of signing. This is also similar for CAdES and XAdES.

• PADES B-B: This is a basic signature. The signature itself must be issued by a certified authority. Its validity can be verified for the duration of the certificate itself. Usually certificates are issued for one or three years. (Revoking a certificate also invalidates it).
• PADES B-T: This is a signature containing an extra time stamp that becomes part of the document in its unsigned data. The stamp then allows the signature to be extended beyond its expiration date for five years.
• PADES B-TL: This type of signature includes both of the above mentioned signatures, and also contains all the necessary materials or references to materials required to validate the signature. These must be contained in the unsigned signature data that is part of the specific document.
• PADES B-TLA: This signature uses the previous variations, but in addition to the above mentioned materials, it must also contain a time stamp for them. This ensures that the data required for verification and the references to it are valid at the time the document is signed.In order to maintain the validity of these documents in the long term, it is necessary to periodically insert the time stamp and thus renew the validity of the entire document.

You can buy Qualified Time Stamp (TSA) on our e-shop as well. 

In practice, B-TL and B-TLA mean that in the referenced document data, for example, lists of revoked certificates from signing certificate authorities must be included, as well as a record of the authenticity of the signatures and other specifications to make them legally verifiable. 

Acrobat Reader can already work with B-B and B-T PDF formats in its basic version. If you have any doubts please do not hesitate to contact us on sales@qscd.eu.