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 making it compliant with the European eIDAS regulation (Regulation on electronic identification and trust services for electronic transactions in the internal market). The eIDAS regulation enhances and repeals the Electronic Signatures Directive 1999/93/EC. EIDAS is legally binding in all EU member states since July 2014. An electronic signature that has been created in compliance with eIDAS has the same legal value as a handwritten signature.
An electronic signature, technically implemented based on PAdES has the status of an advanced electronic signature. This means that
- it is uniquely linked to the signatory;
- it is capable of identifying the signatory;
- only the signatory has control of the data used for the signature creation;
- it can be identified if data attached to the signature has been changed after signing.
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 in the context of electronic signatures
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. Digital signatures are a secure and legally binding means to implement electronic signatures through three cryptographic algorithms:
- the key generating algorithm that randomly selects a private key and its corresponding public key
- the signing algorithm that produces the digital signature from the message and private key
- the signature verifying algorithm that uses the public key, message and digital signature to confirm the authenticity of the message.
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 is complementary to two other standards for an implementation of electronic signatures through cryptographically secured digital signatures in compliance to the eIDAS regulation. Like PAdES, they are legally binding in 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). The PAdES, CAdES and XAdES standards can be downloaded from the ETSI website ETSI download page.
A PAdES-based electronic signature has no admissibility in a court proceeding as evidence. To become admissible it would need to be doted with a digital certificate, encrypted by a security signature creation device ("qualified electronic signature").
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.
Related, there is also TS 103 172: PAdES Baseline Profile
- 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
- SD-DSS : A free and open-source Java library for creating/manipulating PAdES/CAdES/XAdES/ASiC Signatures
- SD-DSS : GitHub repository
- SecureBlackbox : The cross-platform library for creating and manipulating XAdES, CAdES, PAdES and ASiC Signatures
- ETSI PAdES - explored and explained
- OpenCertSign: A free and open-source certificate based PDF signing engine
- PDF Digital Signatures
- ETSI TS 102 778-1 - PAdES Overview - a framework document for PAdES