PAdES (PDF Advanced Electronic Signatures) is a set of restrictions and extensions to PDF and ISO 32000-1 making it suitable for advanced electronic signature. This is published by ETSI as TS 102 778.
While PDF and ISO 32000-1 provide a framework for digitally signing their documents, PAdES specifies precise profiles for use with advanced electronic signature in the meaning of European Union Directive 1999/93/EC. One important benefit from PAdES is that electronically signed documents can remain valid for long periods, even if underlying cryptographic algorithms are broken.
PAdES recognizes that digitally-signed documents may be used or archived for many years – even many decades. At any time in the future, in spite of technological and other advances, it must be possible to validate the document to confirm that the signature was valid at the time it was signed – a concept known as Long-Term Validation (LTV).
The PAdES standard, ETSI Technical Specification (TS) 102 778, introduces a number of adaptations and extensions to PDF to satisfy the Directive's requirements. ETSI will feed these European-specific elements back into ISO for inclusion in the next release of the PDF standard, ISO 32000-2.
PAdES is complementary to two other Electronic Signature concepts also developed by ETSI's ESI committee, both widely recognised within the European Union and suited for applications that do not involve human-readable documents: Cryptographic Message Syntax Advanced Electronic Signatures (CAdES) and XML Advanced Electronic Signatures (XAdES).
An electronic signature is a paperless way to sign a document using a unique credential associated with a given person that is logically attached to or associated with the document, carrying an authority equivalent to a handwritten signature. It can be used to authenticate the signer as well as to detect any changes in the document made after it was signed. Electronic signatures are recognized as a catalyst to electronic commerce, notably Internet transactions. Availability of electronic signature techniques has already been a major stimulus to eBusiness and eGovernment.
For PDF documents, the signature data is incorporated directly within the signed PDF document, much as an ink signature becomes an integral part of a paper document, allowing the complete self-contained PDF file to be copied, stored and distributed as a simple electronic file. The signature can also have a visual representation as a form field, just as it might on a paper document. A significant advantage of PAdES is that it is being deployed by means of widely available PDF software: it does not require development or customization of specialized software.
PAdES Standard (ETSI TS 102 778)
The PAdES ETSI technical specification contains 6 parts:
- Part 1: PAdES Overview – a framework document for PAdES
- Part 2: PAdES Basic – Profile based on ISO 32000-1
- Part 3: PAdES Enhanced – PAdES-Basic Electronic Signatures and PAdES-Explicit Policy Electronic Signatures Profiles
- Part 4: PAdES Long Term – PAdES-Long Term Validation Profile
- Part 5: PAdES for XML Content – Profiles for XAdES signatures of XML content in PDF files
- Part 6: Visual Representations of Electronic Signatures
The PAdES standards can be downloaded from the ETSI download page.
- European Telecommunications Standards Institute (ETSI)
- CAdES, CMS Advanced Electronic Signature
- XAdES, XML Advanced Electronic Signature
- Trusted timestamping
-  Work Program for ETSI TS 102778 - PAdES
- ISO 32000-1:2008 Document of the PDF Standard at the International Organization for Standardization
- PAdES Frequently Asked Questions
- SD-DSS : A free and open-source Java library for creating/manipulating PAdES Signatures
- ETSI PAdES - explored and explained
- OpenCertSign: A free and open-source certificate based PDF signing engine